The Financial Econometrics of Price Discovery and ... · The Financial Econometrics of Price...
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DEPARTMENT OF ECONOMICS
ISSN 1441-5429
DISCUSSION PAPER 06/15
The Financial Econometrics of Price Discovery and Predictability
Seema Narayan and Russell Smyth*
Abstract: This paper reviews recent econometric developments in the literature on price discovery and
price predictability. For both areas, we discuss traditional approaches to econometric
modeling, limitations to these approaches, and recent developments designed to overcome
them. We also discuss the state-of-the-art and suggest future research. Three main
conclusions are drawn. First, while many recent empirical applications in price discovery and
price predictability are on the frontier of econometric methods, further developments are
needed to increase relaxation of relevant assumptions and push the boundaries of
applications. Second, future research in econometric modelling needs to combine/synthesize
recent developments across multiple econometric issues rather than proceeding in a
piecemeal manner, for instance, by integrating developments in the time series literature into
panel-based frameworks. Third, recent econometric literature is generating findings that
challenge long-held beliefs about apparent empirical regularities in price discovery and price
predictability, thus presenting opportunities to develop relevant theory.
JEL Classification Numbers: C53, C58, G12, G13, G14
We thank Paresh Narayan for helpful suggestions on an earlier version of this paper.
© 2015 Seema Narayan and Russell Smyth
All rights reserved. No part of this paper may be reproduced in any form, or stored in a retrieval system, without the prior
written permission of the author
monash.edu/ business-economics
ABN 12 377 614 012 CRICOS Provider No. 00008C
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1. Introduction
The primary motive for investing in domestic or international stocks is to maximize
returns. This, however, encompasses risk, as both return and risk are conceptually tied
to the price of the stock. Given this, an understanding of price formation is
fundamental to achieving higher returns and lowering risks. It is therefore not
surprising that scholars and practitioners in the field of financial economics are
engaged in research that deals with the ‘what’ and ‘how’ of current and future price
formation. The following survey examines the role of econometrics in this venture,
and broadly covers financial econometric developments in the areas of price
discovery and price predictability.
The main reason we focus on price discovery and price predictability together is that
conceptually these two areas of financial economics are related. Dolatabadi et al.
(2014) show that if one can ascertain that in a two-market (say X and Y) setup,
market X dominates market Y in the price discovery process, the implication is that
one can use market X to predict (and also forecast) market Y. To put it differently, the
market with more information can be used to forecast the market with less
information. Price discovery is a first step because it tells us that market X has more
information content than market Y because the former dominates the price discovery
process.
A further reason for considering price discovery and price predictability in the same
review is that not only are these fields of financial economics conceptually related,
but in many respects both areas are informed by similar time series econometric
developments, particularly with respect to integration and cointegration. For example,
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both areas have been informed by developments in unit root and cointegration testing
designed to derive added power, such as the use of panel-based models. Similarly,
both areas have been advanced by ongoing econometric developments designed to
address non-linearities and structural change in data.
The catalyst for many recent econometric developments in both areas is the
theoretical insights of Figuerola-Ferretti and Gonzala (2010). Building on the
components share (CS) methods and a simultaneous price dynamics model proposed
by Garbade and Silber (1983), Figuerola-Ferretti and Gonzala (2010) propose a
theoretical model of price discovery characterized by finite elasticity of supply of
arbitrage services and endogenous convenience yields. Their model demonstrates a
perfect link between an extended Garbade and Silber (1983) framework and the CS
approach, suggesting that the cointegrated vector autoregressive (CVAR) model
(Johansen, 1995) is the natural empirical model to test for price discovery.
This insight is subsequently extended by Dolatabadi et al. (2014a, 2015) to develop a
fractionally cointegrated vector autoregressive (FCVAR) model to examine price
discovery, with the authors showing how CVAR and FCVAR links price discovery
and price predictability. Thus, econometrics developments in both areas are starting to
come together, and it is likely that this convergence will continue in the future.
Consequently, given that there is a theoretical basis to using CVAR/FCVAR to test
for price discovery and price predictability based on Figuerola-Ferretti and Gonzala
(2010) and extensions of their theoretical model, it makes sense to focus on the
evolution of unit root/cointegration testing in both literatures and how these are
linked.
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It should be noted that in chronicling the development in financial econometrics in the
period 1980-2000, Bollerslev (2001) argues that time-varying volatility models (such
as ARCH/GARCH and stochastic volatility formulations) and robust methods-of-
moments-based estimations procedures (such as Generalized Methods of Moments)
stand out as milestones. We do not review these important developments, however, as
there are already several broad textbook treatments (see e.g. Campbell et al., 1997) as
well as surveys on ARCH/GARCH and stochastic volatility/realized volatility (see
Bollerslev et. al., 1992, 1994; Engle, 1995; Ghysels et al., 1996; Shephard, 1996;
Barndorff-Nielsen and Shephard, 2014; Bollerslev, 2010; see also Bollerslev and
Hodrick, 1995; Pagan, 1996; Bollerslev, 2001).
The structure of the survey is as follows. For both topics the main areas covered will
be symmetric, namely: motivation and implications; overview of existing studies;
state of the art econometric techniques; and suggestions for future research.
2. Price Discovery
2.1 Motivation and implications
Price discovery refers to the means through which information is transformed into
prices. The price discovery literature centers on the speed at which related markets
reach the equilibrium asset price, with the market in which new information is
reflected most rapidly considered to be the one with the price discovery function.
There are multiple factors motivating studies of price discovery in financial markets.
Improved understanding of price discovery not only assists investors to make better-
informed decisions, but because it involves knowing how information translates into
price across closely related markets, it facilitates risk management (Westerlund et al.,
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2014). Improved understanding of price discovery also facilitates more efficient asset
evaluation. Evidence from experiments suggests that trading the same asset across
two markets simultaneously increases the speed at which efficient prices are reached
(Forsythe et al., 1982, 1984). Given this, better understanding of the transmission
mechanism of information across markets, and the rate at which information is
reflected in prices, can provide evidence on the relative efficiency of markets.
Studying price discovery also provides insights into how markets incorporate new
information about asset values, as well as the relative importance of fundamentals and
speculation in this process. For example, the lead-lag relationship between spot and
future markets has implications for evaluating the role of speculation in driving
commodity prices. If price discovery occurs in the futures market, this suggests that
speculation is driving commodity prices; however, if price discovery occurs in the
spot market, the implication is that changes in market fundamentals are driving
demand and supply (hence prices) for the commodity (Kaufmann and Ullman, 2009).
Price discovery also has implications for the preferred markets in which informed
traders invest. If price discovery occurs in futures markets, this implies that informed
traders might prefer to trade in futures markets rather than spot markets.
2.2 Types of price discovery in financial markets
There are at least three related sets of studies in the price discovery literature. One set
of studies estimates the information share of each market for fragmented securities
traded across multiple markets (see e.g. Eun and Subherwal, 2003; Harris et al., 1995,
2002; Hasbrouck, 1995). There has been a surge in the number of studies of this sort,
which at least in part reflects growing market fragmentation (De Jong and Schotman,
2010; Westerlund et al., 2014). The principal finding from these studies is that price
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discovery predominantly occurs in the home market, and that prices in the foreign
market adjust to the home market. Notwithstanding, evidence exists that the relative
importance of home and foreign market may change over time, particularly if there
have been financial crises (Caporale et al., 2014; Fernandes and Scherrer, 2014).
A second set of studies estimates the information share of each market across
interconnected markets such as spot and futures markets (see e.g. Stein, 1961;
Hasbrouck, 1995; Gonzalo and Granger, 1995). While findings vary across
commodities, most studies find that price discovery occurs in the futures market.
There is, however, slightly more evidence of price discovery in the spot market using
a fractionally cointegrated model (Dolatabadi et al., 2014, 2015).
A third set of studies estimates the information share across markets for a particular
product. An example is Westerlund et al.’s (2014) study that investigates which
country leads the price discovery process for crude oil. These authors examine oil
prices in the United Kingdom, United States and Oman and find that price discovery
occurs in Oman, reflecting the fact that it is the dominant oil producing market.
2.3 Econometric issues in modeling price discovery
The econometric approach to modeling price discovery involves three steps. The first
is to ascertain the order of integration of asset prices as a precursor to examining
whether there is a long-run relationship between the markets. If two markets are
theoretically linked, it follows that any shock in the form of new information will
affect both markets. The second step is to establish if prices across the markets are
cointegrated. If prices are cointegrated, the question becomes which of the
cointegrated markets is the first to absorb the new information. The third step is to
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determine in which market price discovery occurs. This is done either through
examining the error correction coefficient to ascertain the relative speed of adjustment
to the long-run equilibrium price (Gonzalo and Granger, 1995), or estimating the
information shares from the error correction model (Hasbrouck, 1995).
2.3.1 Static measures of price discovery
The two main static approaches to measuring price discovery are the information
share (IS) method (Hasbrouck 1995) and the component share (CS) method that relies
on a permanent-transitory decomposition of the cointegrated system (Gonzalo and
Granger, 1995; Harris et al., 1995, 2002). Both approaches are reliant on the vector
error correction model (VECM) proposed by Engle and Granger (1987). The
approaches differ, however, in that Gonzalo and Granger (1995), and Harris et al.
(1995, 2002) focus on the proportion of each market’s innovation that contributes to
the common efficient price, while Hasbrouck (1995) focuses on the proportion of the
variance in the common efficient price that can be attributed to individual markets.
An alternative way of seeing the difference in the approaches is that Gonzalo and
Granger (1995), and Harris et al. (1995, 2002) define price discovery in terms of the
speed of adjustment to the long-run equilibrium based on the error correction
mechanism, while Hasbrouck (1995) defines price discovery in terms of the
information share.
2.3.2 Limitations of the CS and IS methods
The main limitation of both the CS and IS methods is the very fact that they are static
approaches to price discovery; as such, they are based on market innovations in their
reduced form (Scherrer, 2012). However, as price discovery is inherently a dynamic
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process in which shocks to prices are likely to be correlated, neither of these static
methodologies is able to address the price dynamics involved (Lehmann, 2012). The
only way to properly address the price dynamics involved in price discovery is to
adopt a structural measure of price discovery in which changes in structural
innovations can be appropriately attributed across markets (Scherrer, 2012; Yan and
Zivot, 2010).
A second problem is that the CS approach to price discovery is premised on
adjustment to the long-run equilibrium price being continuous and linear. For
example, this is implicit in the assumption made by Harris et al. (1995, 2002).
However, there are several reasons to doubt that adjustment is continuous and linear
due to market frictions in the presence of policy interventions and transaction costs.
Clearly, market frictions can be explicit or implicit (Gagnon and Karolyi, 2010).
Examples of potential explicit market frictions impeding linear adjustment include
holding costs (e.g. lending fees, unrealized interest on short-sales proceeds and
opportunity cost of capital), short-sale restrictions, taxation and transaction costs (e.g.
bid-ask spreads on cross-listed pairs, and foreign exchange and commission) (Chen et
al., 2013). Implicit market frictions can be due to cross-border differential adverse
selection risks and agency walls between arbitrageur and client (Shleifer and Vishney,
1997). Further, if speculators are active in the spot market-futures market, their
trading may destabilize the market and generate a potential non-linear effect of
hedging relative to speculation in the futures market’s share of price discovery
(Chang et al., 2013).
A third limitation of the CS model relates to the time-varying nature of price
discovery. Several studies in related branches such as cointegration show that markets
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are characterized by time-varying variance and co-variance. Hence, this time-varying
characteristic should have implications for price discovery. What this means is that
there may be phases of time over which market X will dominate price discovery,
while in other phases it may well be that market Y will dominate price discovery.
This will particularly be the case for markets such as oil prices that are prone to
volatility (Bessembinder et al., 1995). This is problematic, for example, when
examining the price adjustment process in futures markets, in which switches under
different market conditions can be expected to induce shifts in the adjustment process
to restore the cost-of-carry relationship (Brenner and Kroner, 1995; Caporale et al.,
2014).
A fourth limitation with both the CS and IS approaches is that neither allows for the
possibility of fractional cointegration. In the context of spot and futures markets,
several studies find evidence of fractional integration in the forward premium (see
e.g. Baillie and Bollerslev, 1994; Maynard and Phillips, 2001). Hence, fractional
integration in the forward premium implies that spot and futures prices are
fractionally cointegrated. The reason for this is that although the spot and futures
prices themselves may be integrated of order 1 (I(1), the spread between spot and
futures prices will be fractionally integrated of a lower order (Doltabadi et al., 2014).
A fifth limitation of the original CS and IS frameworks is that the microstructure
models are limited to two markets. This means that the frameworks do not have the
ability to allow for price discovery across multiple markets simultaneously. It also
means that, as with any time series measure, that power of the unit root and
cointegration tests are limited by the time series and fail to exploit the additional
power in a panel.
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The final limitation is the econometric challenge in estimating price discovery. The
measures are not easy to estimate in practice, however, as they very technical, involve
several steps, and are econometrically burdensome. In other words, unlike tests for
cointegration which are built into standard software packages and for which many
codes are available, the same is not true for price discovery estimators. This thereby
limits the application of these tests despite their merits.
2.3.3. Extensions of the CS and IS methods
The CS and IS methods have been extended in various directions to address each of
these limitations. First, the fact that the CS and IS frameworks are unable to capture
price dynamics has led to the development of structural models of price discovery that
allow for changes in structural innovations to be correctly assigned to markets (see
e.g. Yan and Zivot, 2010, 2010a; Kim, 2010; Scherrer, 2012). Yan and Zivot (2010)
propose the first two-variable structural model of price discovery in which they
consider only one common factor. The authors apply their model to the Euro/Yen
exchange rate and find that price discovery in this market occurs through the US
dollar market. Kim (2010) expands the Yan and Zivot (2010) framework to a three-
variable model, sharing two common variables or one cointegrating vector.
Scherrer (2012) presents a structural model of price discovery for a seven-variable
model. She first uses the Gonzalo and Granger (1995), and Gonzalo and Ng (2001)
method to retrieve permanent and transitory innovations from market residuals in
their reduced form. The author then modifies Gonzalo and Ng’s (2001) method to
allow the variance of the structural innovations to differ from the identity matrix,
which works well with up to three common factors. One advantage of Scherrer’s
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(2012) approach compared with those of Kim (2010), and Yan and Zivot (2010) is
that the innovations attached to each of the three common factors are allowed to
contemporaneously correlate. Another advantage is that Scherrer (2012) decomposes
the covariance matrix of the reduced innovations in such a manner that common
factors may impact all prices in the long run. The author applies her method to
examine price discovery for Brazilian firms cross-listed in Brazil and the United
States using high frequency data. She finds that price discovery occurs on the
Brazilian stock exchange in the short-run, but that in the long run both exchanges are
equally important. Scherrer (2012) presents Monte Carlo evidence suggesting that her
structural model outperforms that proposed by Yan and Zivot (2010).
Second, the assumption of continuous and linear adjustment has been relaxed in
studies that develop threshold cointegration/error-correction models. Chen et al.
(2013) extends the CS method to consider the exchange-respective information shares
in Canadian firms cross-listed in Canada and the United States, while Chang et al.
(2013) builds on the IS method to examine the effect of non-linearities in the futures
market on price discovery in the foreign exchange futures market.
Chen et al. (2013) first use Balke and Fomby’s (1997) threshold cointegration model
and then, because dynamics may alternatively be gradual, generalize it to a smooth
transition version. Their information share measures are obtained from outer-regime
adjustment coefficients based on a two-regime threshold ECM and average
coefficient estimates based on a smooth transition ECM. Chen et al.’s (2013)
approach has the advantage in that it takes into account non-linearities associated with
both abrupt and smooth party changes due to market frictions. Their approach
captures the relative contributions to price discovery with a higher degree of precision
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compared with, for example, the ECM in Harris et al. (1995, 2002), which does not
address the time-and regime-contingent characteristics of information shocks.
In a related contribution, Chang et al. (2013) examine the effect of the relative size of
hedger and speculator open interests on price discovery in the foreign exchange
futures market. They first use the IS approach of Hasbrouck (1995) to ascertain the
contribution of the EUR-USD and JPY-USD futures markets to the futures/spot price
discovery process. With the IS for the futures market, they then estimate a logistic
smooth transition model to ascertain how price discovery depends on the trading
positions held by hedgers and speculators in the futures markets. Chang et al. (2013)
find a non-linear relationship between speculative trading volume and the efficacy of
trading volume, in which the effect of speculative trading volume on market
efficiency depends on its relation to endogenously determined thresholds.
Third, to accommodate structural change, models have been developed that allow for
time varying price dynamics. For example, Caporale et al. (2014) build on the CS
approach to take into account parameter instability in the price discovery process.
Specifically, in order to detect structural changes in the adjustment coefficients, they
estimate time-varying parameter models for the loading weights using a Kalman filter
approach. Kalman filtering has the advantage that it does not impose a priori
restrictions on the timing of structural breaks, making it useful to ascertain and
interpret the effect of any financial turmoil on price discovery. Caporale et al. (2014)
apply their model to price discovery in crude oil spot and futures. One interesting
conclusion to emerge from their study is that while futures markets play a more
important role in price discovery than spot markets, their relative contributions exhibit
high instability. Another interesting finding is that spot markets become more
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important for price discovery in times of financial crisis such as the Global Financial
Crisis.
Fourth, the assumption of a I(0)/I(1) distinction has been relaxed in studies that
examine price discovery using FCVAR. Dolatabadi et al. (2014a, 2015) extend
Figuerola-Ferretti and Gonzalo’s (2010) model to develop a fractionally cointegrated
equilibrium model, with Dolatabadi et al. (2015) using this new model as the
theoretical basis on which to apply FCVAR to price discovery in spot and futures
markets.
As outlined in Dolatabadi et al. (2014a, 2015), the main advantage of the FCVAR
model lies with its flexibility. It permits one to ascertain the cointegrating rank and to
jointly estimate the adjustment coefficients and cointegrating relations while
accounting for the short-run dynamics. Dolatabadi et al. (2015) find that generally the
fractional cointegration parameter is significant, suggesting that a non-fractional
model is inappropriate. The authors also find that, when allowing for fractional
integration in the long-run equilibrium relations, fewer lags are needed in the
autoregressive augmentation of the model, which underpins the utility of the
fractional model. Their main substantive finding is that when applying the fractional
model, the spot market is slightly more important in the price discovery process
relative to the futures market compared with the non-fractional model.
Fifth, the power limitations associated with short time series have been addressed by
the development of panel data models of price discovery. De Jong and Schotman
(2010) generalize the IS framework to multiple markets. In contrast to the traditional
information share that is defined within a reduced-form time series model, De Jong
and Schotman (2010) define the information share directly from the unobserved
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components model. This approach avoids the wide information share bounds one
sometimes gets when using the Hasbrouck (1995) VECM (see e.g. Covrig and
Melvin, 2002), particularly in settings in which there are multiple dealers and
markets.
More recently, Narayan et al. (2014) propose a panel model in which, conditional on
finding panel cointegration, a panel VECM is specified. The panel VECM is used to
extract the price discovery coefficients, thus extending the CS and IS frameworks.
The conventional panel VECM, such as that proposed in Narayan et al. (2014), has
the limitation that if one considers a large number of exchanges (prices) then the
model becomes over-parameterized. This comes at the cost of precision in estimation
of price discovery. Narayan et al. (2014) only have two price variables and so escape
this criticism. However, in most other literature the subject of price discovery
involves multiple exchanges, which inhibits the utility of using this approach.
Building on the CS and IS frameworks as well as on De Jong and Schotman (2010),
Westerlund et al. (2014) propose a panel data model of prices that have a common
factor representation and in which prices are modelled as non-stationary and
cointegrated processes. The Westerlund et al. (2014) factor-based panel model is
motivated in part by the need to address the econometric complexities with measuring
price discovery. Their proposed test is simple and easy to estimate compared to the
Generalized Methods of Moments test of De Jong and Schotman (2010), and has two
advantages. First, it is free from the limitations of the panel VECM used in Narayan et
al. (2014) in that it neither restricts the time-series dimension nor the cross-sectional
dimension. Thus, the concern of over-parametrizing the model with the traditional
panel VECM is addressed. Second, with existing price discovery tests, there are
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restrictions on short-term (transitory) and long-term (permanent) shocks. However,
because the Westerlund et al. (2014) test is built on a factor model, it does not impose
these restrictions. With the Westerlund et al. (2014) test, all shocks are entertained in
their original form, that is, without any restriction.
2.4 State of the art
The above discussion suggests that by using the CS and IS frameworks as its starting
point the price discovery literature has followed two directions. One involves
developing panel models of price discovery, while the other focuses on relaxing
various assumptions of the standard IS and CS frameworks in a time series context.
Perhaps the nearest to the state-of-the-art in the traditional IS/CS framework is the
seminal ‘unifying’ contribution of Figuerola-Ferretti and Gonzalo (2010), who
demonstrate that the Garbade and Silber (1983) framework coincides exactly with the
permanent component in the Gonzalo and Granger (1995) permanent-transitory
decomposition. This has paved the way for treating the CVAR model as the natural
model to analyze price discovery, and provided a relatively simple way of
ascertaining which of two prices is dominant in terms of long-run price discovery.
Figuerola-Ferretti and Gonzalo’s (2010) framework, however, no longer represents
the state-of-the-art in price discovery per se. Other models have been developed to
address the limitations of the CS/IS framework, with Figuerola-Ferretti and Gonzalo’s
(2010) framework now serving as a platform for the FCVAR proposed by Dolatabadi
et al. (2015, in press) Further, the CS and IS frameworks have been extended in other
directions, including the development of structural models to better model price
dynamics, models that take into account non-linearities or structural change, as well
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as panel models to deal with multiple markets and/or small time series. Because these
contributions emanate from myriad directions, it is difficult at this point to pinpoint
one state-of-the-art method for determining price discovery. The preferred model
really comes down to the issue affecting price discovery that one wants to focus on.
Perhaps the most that can be said is that these developments are at the frontier and in
compact represent the state-of-the-art in modeling price discovery.
2.5. Suggestions for future research
Given that the time series literature has moved in two directions, namely, the
development of panel models and relaxing assumptions underpinning the CS and IS
frameworks, one avenue for future research could be to integrate some of the
developments of these two avenues of inquiry into a panel framework. Obvious
examples would be to incorporate non-linearities, structural change or fractionally
integrated processes into recently proposed panel models.
A second avenue for future research could be to further develop structural models of
price discovery. The most general model of this form in the literature appears to be
from Scherrer (2012), who presents a method to measure the instantaneous effects of
permanent shocks on prices. Her model allows the observed price to depend on three
common factors, which are allowed to be contemporaneously correlated, providing
the required conditions for linkages across common factors. One potential extension
to the Scherrer (2012) framework could be to extend the number of common factors.
A third direction for future research could be to develop regime switching price
discovery models, which may be sufficient to allow an examination of price discovery
during economic expansions and recessions about which nothing is known.
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A fourth direction for future research in this area could follow on from recent
developments in econometric modelling rather than extending its frontier. Recent
innovations in econometric modelling have challenged long-held beliefs about the
markets in which price discovery occurs. One example is that incorporating fractional
cointegration seems to provide more evidence that price discovery occurs in the spot
market. Another example is that allowing for the effects of financial crises suggests
that incorporating time-varying dynamics provides evidence that fundamental factors
may have a greater role in driving prices, particularly in periods of financial crises.
Future research could address why one finds more evidence of price discovery in
specific spot markets with fractional integration or time-varying dynamics given the
economic fundamentals in particular markets.
3. Price Predictability
3.1. Motivation and implications
Two variables that commonly appear in the financial econometrics literature on
predictability are securities and exchange rates. Prior to the seminal review by Fama
(1970), empirical studies provided strong evidence that securities’ markets are
predictable using past returns. Fama (1970) defines this form of return predictability
as the weak form of the efficient market hypothesis (EMH). However, relying only on
past returns lacks power as past realised returns are noisy measures of expected
returns (Fama, 1991). To improve the power of return predictability tests, predictor
variables that are less noisy proxies for expected returns could be used (Fama, 1991).
Some early evidence that short-horizon returns can be predicted from past values of
other financial and macroeconomic variables include expected inflation (Bodie, 1976;
Fama, 1981), short-term interest rates (Fama and Schwert, 1977), dividend yields
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(Rozeff, 1984; Shiller, 1984; Fama and French, 1988), and earnings to price ratios
(Campbell and Shiller, 1988), all of which are able to explain a larger fraction of the
return variation for longer return horizons. In the past three decades an influx of other
predictors of stock markets has appeared in the literature, including the seminal work
of Campbell and Shiller (1988) that shows that market returns can be predicted to
some extent by using financial ratios such as dividend yields and price-earnings ratios
(see Fama, 1991, and Malkiel, 2004, for a discussion of the success of past studies in
predicting future equity returns).
The success of predictability studies in the 1980s and 1990s led many studies to
question the EMH, although Fama (1991) suggests that the results can be achieved
within the confinement of rationality, thus extending the definition of the weak-form
EMH to include past movements in variables other than past returns (see also Lim and
Brooks, 2009). However, many studies, particularly in the behavioural finance
literature, conclude that investors are prone to irrational behavior (or psychological
pitfalls); hence, this implies the potential to make abnormal profits (see Malkiel,
2003; Schwert, 2003; Malkiel et al., 2005; Lo, 2004; Yen and Lee, 2008). This
change in attitude towards stock market predictability has been fuelled by the growth
of computer power and has led to the development of a number of estimation and
predictability techniques.
Thus, while testing exchange rate predictability is strongly supported by economic
theory, the challenge since Meese and Rogoff (1983) has largely remained one of
finding predictive models for the exchange rate beyond the simple random walk
model.
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The rest of this part of the survey is concerned with financial econometric
developments in the predictability literature on securities and exchange rates – by far
the most common financial variables covered in this literature. Our focus is on the
predictability of these two variables using past values of financial and macroeconomic
variables. Although this literature is vast, our particular focus is on advances in
econometric techniques. We initially provide an overview of predictive modelling
using unrestricted and restricted vector autoregressions (VARs), including both panel
and time series analyses. This is followed by a review of recent developments in
financial econometrics in forecasting financial variables.
3.2. Predictive modelling using unrestricted and restricted VARs
Sims (1980) highlights the importance of the VAR formulation as a convenient
representation for forecasting and estimation, while Engle and Granger (1987)
establish that an error correction framework provides the means for testing, estimating
and forecasting a cointegrated system (see also Engle et al., 1989; Christoffersen and
Diebold, 1998). Engle and Yoo (1987) illustrate that when the unrestricted VAR (in
levels) is compared to cointegrated systems, it leads to suboptimal forecasts at the
longer horizon. Hence, they conclude that it is important to “build models designed
for cointegrated time series or vector autoregressive error-correction models
(VECMs)” (p. 159) (see also Phillips, 1998; Hoffman and Rasche, 1996; Clement and
Hendry, 1995).
The advancement of this technique as a forecasting tool has also gone hand-in-hand
with the quest to explain foreign exchange rate behavior within the confines of the
monetary model of exchange rate. Indeed, a long-run cointegrating relationship
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between the exchange rate and monetary fundamentals is a central tenet of the
monetary model of the exchange rate. Thus, if this model depicts the long-run
behavior of the exchange rate correctly, then the exchange rate only deviates from
monetary fundamentals in the short-run, making the vector error correction model
(VECM) in forecasting exchange rates a natural contender (see also Groen, 2005).1
While early studies such as Mark (1995), Chin and Meese (1995), and Groen (2000)
show the importance of first establishing the cointegration relationship between the
monetary fundamentals and exchange rate in the exchange rate predictability exercise,
predictability in these studies has been confined only to the long horizon. These long
horizon-to-weak-to-no predictability results, however, have fueled a search for a more
versatile, efficient and powerful error-correction framework predictability test.
In terms of versatility then, and unlike Engle and Granger’s (1987) test, Johansen
(1988, 1991) allows for more than one cointegrating relationship. The autoregressive
distributed lag (ARDL) - bounds testing methodology of Pesaran and Shin (1999),
and Pesaran et al. (2001) allows for a mixture of I(0) and I(1) variables, provides for
more variables to enter the long run model, and has been proven useful in predicting
long-run asset returns. The fractional cointegration test developed by Johansen (2008)
is suitable for several financial variables well described by long-memory fractionally
integrated processes, and has also been proven useful in explaining the return-
volatility relationship (see e.g. Bollerslev et al., 2013). With evidence of parameter
instability in the exchange rate as well as in the stock market, this time-varying
cointegration approach represents a logical tool. Further, Park and Park (2013) show
that the time-varying approach has strong predictive power for future changes in
1 Hence, predictability of exchange rates and econometric developments in the area of predictability
using the VECM framework have gone hand-in-hand.
20
exchange rates through in-sample and out-of-sample analysis.
In order to address the low power of time series, the Engle-Granger type tests have
also followed developments in testing for a unit root. The predictability literature has
also analyzed time series across similar cross-sections in panel datasets. As
Westerlund and Narayan (2014c, p. 2) point out, “…the use of panel rather than time
series data not only increases the total number of observations and their variation, but
also reduces the noise coming from the individual time series regressions. This is
reflected in the power of the resulting panel predictability test, which is increasing in
both N (number of cross-sections) and T (time span), as opposed to a time series/unit-
by-unit approach where power is only increasing in T. Thus, from a power/precision
point of view, a joint (panel) approach is always preferred. Furthermore, since power
is increasing in both N and T, this means that in panels one can effectively
compensate for a relatively small T by having a relatively large N, and vice versa”.
As indicated above, the panel version of the Engle and Granger (1987) test involves
estimating the panel long-run model with a panel unit root test (see e.g. Levin et al.,
2002; Im et al., 2003) being conducted on the residuals. This approach implies both
homogeneous long-run coefficients and homogenous adjustment parameters, with
only the serial correlation in the residuals panel unit root test assumed to be
heterogeneous (Groen, 2000). Error-correction based forecasting models from these
techniques have the disadvantage that the differences in the speed of adjustment and
dynamics across different countries are not taken into account (see e.g. Groen, 2000).
Commonly used variants of the panel-based Engle-Granger approach are the Pedroni
(1995), and Kao (1997) tests, which assume heterogeneity in the model parameter and
21
statistics. These tests are based on cross-sectional averages of the individual
parameters and statistics. However, because these parameters and statistics are
independent, Groen and Kleibergen (2003) argue that these tests do not capture the
panel dimension that is crucial to enhance the power of cointegration tests. Thus, to
allow for interdependence between panels, Groen and Kleibergen (2003) stack a fixed
number of VECM of different individuals into a joint panel VECM and develop a
likelihood-based framework for cointegration analysis, generalising Johansen (1988,
1991) (see also Larsson et al., 2001).
These aforementioned tests have become increasingly efficient over time as they
incorporate better estimating procedures for forecasting parameters. For example,
apart from using ordinary least squares (OLS) as the standard estimation method,
methods such as fully-modified OLS (FMOLS) and dynamic ordinary least squares
(DOLS) (see Saikkonen, 1991; Stock and Watson, 1993; Kao and Chiang, 2000) have
been developed for time series and panels, with Kao and Chiang’s (2000) examination
of the finite-sample properties of the DOLS estimator finding it to be superior to both
OLS and FMOLS in panel regressions.
In panel-based forecasting analysis, it has become common to pool the parameters of
the forecasting equation, as in Mark and Sul (2001). Using simulations, Westerlund
and Basher (2007) show that pooling individual prediction tests (such as the Theil U
statistic and the S prediction statistics of Diebold and Mariano, 1995) can lead to
substantial power gains. These authors further show that pooling only the parameters
of the forecasting equation does not seem to generate more powerful tests.
22
3.3.Developments in econometric modelling of forecasting financial variables
Beginning with Mankiw and Shapiro (1986), and Stambaugh (1986), innovation in
financial econometrics in the predictability literature over the past three decades has
primarily addressed various challenges which we characterize under three broad
topics. These include the salient features of the predictive models and its predictors,
predictability in the presence of model instability and uncertainty, and combination
forecasts. We focus on each of these three areas in turn.
3.3.1 Salient features of predictive models
(a) Persistent regressors
There is now strong evidence that widely accepted predictors of excess returns (such
as dividend-price ratio, earnings price ratio and measures of interest rates) are
persistent and behave like non-stationary variables, although they may not be fully
integrated (see Campbell and Yogo, 2006; Lewellen, 2004; Torous et al., 2004).
Meanwhile, the dependent variable (e.g. excess returns) may exhibit less persistence
than their predictors (Maynard et al., 2013). Cavanagh et al. (1995) show that
classifying the predictor variables as I(0) or I(1) leads to large size distortions when
regressors have local-to-unit roots. Predictability studies indicate that ignoring this
persistence in the regressors can lead to over-rejection of the null hypothesis using
conventional critical values (Campbell and Yogo, 2006; Torous et al., 2004).
Furthermore, Phillips and Magdalinos (2007a, b), and Magdalinos and Phillips
(2009a) recently analysed a wide range of close-to-unity processes and named those
in the vicinity of stationary, but not quite stationary, as mildly integrated processes.
Many variables, including Treasury Bill rates, show varying degrees of persistence
and seem to be mildly integrated processes.
23
While Phillip and Lees (2013) only recently accounted for the mildly integrated
process in predictive regression methodology, there are several studies in the
predictability literature that have paid attention to nearly integrated variables. Elliot
and Stock (1994), for instance, propose an asymptotic framework in which the
regressor is allowed to follow an autoregressive process with a root near to unity so
that it approximates a finite sample distribution of test statistics when the predictor is
persistent. However, allowing for persistence in the regressor leads to a nonstandard
limit distribution of the t-statistic that becomes dependent on a nuisance parameter,
and this cannot be consistently estimated (see Cavanagh et al., 1995; Torous et al.,
2004; Campbell and Yogo, 2006). Torous et al. (2004), and Campbell and Yogo
(2006) are other studies that develop asymptotics for inference using a local-to-unity
autoregressive specification for a single regressor. The Campbell and Yogo (2006)
method has been particularly popular among empirical researchers, is an industry
standard in finance, and provides a benchmark for competitors (Phillips, 2014, p.
1191).
These aforementioned studies follow Cavanagh et al. (1995), and use Bonferroni
intervals of the coefficient (of the predictor variables) in which the dependence from
the localising coefficient, c, is eliminated. Nonetheless, Bonferroni-type modelling
requires simulations to compute critical values to perform inference and confidence
interval construction, since the limit distribution employed in the calculations is
nonstandard (Phillips and Lee, 2013). These tests are also difficult to extend beyond
one regressor, which is not a desirable feature as there are typically several predictors
for each financial variable (Phillips and Lee, 2013). Furthermore, empirical size may
be substantially lower than nominal size and result in a conservative test. Cavanagh et
24
al. (1995) suggest aligning the nominal size to a desired level asymptotically (see
Torous et al., 2004), while Phillips and Less (2013) argue that the power of the
conservative test is often negligible in near local alternatives to the null of non-
predictability.
To address the uncertainty surrounding the root, these papers follow Stock (1991) to
construct confidence intervals for the largest autoregressive root of many explanatory
variables used in predictive regressions. However, Phillips (2014) shows that Stock’s
confidence intervals for the root are invalid and seriously bias asymptotically when c
→ −∞. This failure in the approach leads to poor performance in predictive regression
tests based on Bonferroni methods when the regressor is stationary or mildly
integrated (Phillips, 2014). Elliott et al. (2012) develop a ‘nearly optimal’ test so that
the procedure does not suffer from the problems inherent in the Campbell–Yogo test.
Furthermore, as Phillips (2014) argues, the computational and design considerations
make this method most useful in the single regressor case.
Finally, in these local-to-unity cases, the finite sample bias in estimation (discussed
below) is still present in the limit, and correcting the asymptotic bias is generally not
possible since the bias depends on the localizing coefficient, c, and this parameter is
not consistently estimable (Phillips and Lee, 2013). Lewellen (2004) extends the work
of Stambaugh (1999) to account for the finite sample bias and persistence in the
regressor. Lewellen uses conditional tests (which are estimated from OLS) to show
that predictability can be improved if information in the predictor autocorrelation,
especially when it is close to one, is utilized. Other approaches also provide solutions
to the nonstandard and non-pivotal limit distribution problem, including the
25
conditional likelihood approach with sufficient statistics developed by Jansson and
Moreira (2006), a control function approach by Elliott (2011), and the instrumental
variable (IVX) approach proposed by Magdalinos and Phillips (2009b) (see Phillips
and Lee, 2013, for a detailed discussion of each of these approaches).
In particular, Phillips and Lee (2013) extend Magdalinos and Phillips (2009b) IVX
approach to solve most existing problems in predictive regression methods. The IVX
approach generates a less persistent instrument for the regressor (X) than the regressor
itself, which uses no extraneous information so that the instrument relies only on the
regressor. Phillips and Lee (2013) add to this by allowing for multivariate regressors,
including predictive processes whose roots may lie in a wide vicinity of unity and
mildly integrated, local-to-unity and unit root regressors, all of which are examined
with standard chi-square tests and can be applied easily to long-horizon predictive
regressions. While the implementation of this approach is by straightforward linear
regression, the method requires user input on the parameter choice for instrument
construction (Phillips, 2014).
The above studies address size distortions in the context of the local-to-unity case.
However, persistence can also manifest itself in the form of long memory (Maynard
et al., 2013). Fractionally differenced processes can be observed in several predictors
such as forward premium (Baillie and Bollerslev, 1994; Maynard and Phillips, 2001),
volatility (Comte and Renault, 1998; Baillie and Bollerslev, 2000) and dividend yields
(Koustas and Serletis, 2005).
26
Maynard et al. (2013) develop a predictive test based on a two-stage rebalancing
procedure in which a semiparametric or parametric estimator may be used to estimate
the degree of long memory in the regressor in the first stage. In the second stage, the
regression is rebalanced by fractionally differencing the regressor. This also
rebalances the alternative hypothesis while leaving the null hypothesis unchanged and
thus allowing for a valid test of non-predictability. The authors’ Monte Carlo study
confirms that fractionally differencing the regressor removes the source of the size
distortion and yields a t statistic in the second-stage regression with correct size. They
also find that estimation and inference in the second stage are robust to estimation
error or even modest misspecification in the first stage.
The latter result has connections with recent studies that show that the functional form
may affect the power of predictive tests under non-stationarity with a parametric
approach (Kasparis et al., 2014). And this also may be true for some nonparametric
nonstationary specifications (Wang and Phillips, 2009). With this in mind and using
the recent work of Wang and Phillips (2009), Kasparis et al. (2014), in particular,
develop a unifying framework for inference in predictive regressions where the
predictor has unknown integration properties. They propose two easily implemented
nonparametric F-tests in which limit distributions is nuisance parameter free and
holds for a wide range of predictors, including stationary as well as non-stationary
fractional and near unit root processes. Kasparis et al.’s simulations suggest that this
test is more powerful than existing parametric tests (e.g. Jansson and Moreira, 2006)
when deviations from unity are large or the predictive regression is nonlinear.
Karemera and Kim (2006) suggest that using long memory models for forecasting
nominal exchange rates is a viable alternative to conventional models. They show that
27
an autoregressive fractionally integrated moving-average (ARFIMA) model is more
efficient than the random walk model in steps-ahead forecasts beyond one month. The
authors also find it to be more efficient than the random walk model in multi-step-
ahead forecasts.
(b) Endogeneity
In financial predictive models where returns are regressed on a lagged predictor
variable (whether for exchange rates or stocks), the regression results will suffer from
small sample bias if the regression disturbances are correlated with the predictor’s
innovations. This creates the so-called embedded endogeneity problem that leads to
biased estimates. Stambaugh (1999) illustrates through the example of excess stock
returns and dividend yield that in the presence of this bias, “…finite-sample
estimation and inference become less straightforward, for at least two reasons. First,
the ordinary least squares (OLS) estimators, although consistent, are biased and have
sampling distributions that differ from those in the standard setting. Second,
differences between classical and Bayesian methods become more apparent in the
presence of this Stambaugh bias, whereas those approaches are distinguished less
often in the standard regression setting”. Stambaugh’s (1999) approach to accounting
for endogeneity applies in the case of a single predictor, while more recently, Amihud
and Hurvich (2004), and Amihud et al. (2009) account for endogeneity in the
presence of multiple predictors. Furthermore, Stambaugh accounts for endogeneity
assuming that the predictive regressor’s stochastic explanatory variable is stationary.
Lewellen (2004) allows for a persistent regressor and Stambaugh’s bias in his study,
and shows that without accounting for persistence the corrections for small sample
biases can substantially understate forecasting power.
28
Similarly, Cai and Wang (2014) are concerned with the presence of endogeneity in
the model and persistence of the regressor, although their approach is different from
Lewellen (2004) because they work with multiple predictors. Cai and Wang (2014)
address endogeneity by adopting the Amihud and Hurvich (2004), and Amihud et al.
(2009) linear projection method, and then using a two-step estimation procedure to
manage both highly persistent and non-stationary predictors.
(c) Heteroskedasticity
Another important feature of financial predictive regression is the presence of noise or
time-varying ARCH/GARCH effects in asset returns. The long horizon predictive
regressions as in Torous et al. (2004 in which the predictor variable may be monthly
but the returns variable can be measured over one, two, or five year/s, have long been
used as a way to reduce noise in stock returns (Campbell and Yogo, 2006). This is
because, under the alternative hypothesis that returns are predictable, the variance of
the return increases less than proportionally with the investment horizon (Campbell
and Yogo, 2006). Compared to the long horizon tests, the procedures proposed in
Lewellen (2004), and Campbell and Yogo (2006) are even more powerful as they
reduce noise not only under the alternative hypothesis, but also under the null.
Westerlund and Narayan’s (2014b) study proposes a test that exploits the information
contained in the heteroskedasticity of returns, which is found to lead to higher power.
Similar to the above studies, their generalised least squares (GLS) test accounts for
persistence in regressors and endogenity issues. The asymptotic test’s dependence on
nuisance parameters reflecting persistence, endogeneity and heteroskedasticity in the
data, however, means that the test can suffer from size distortions. To account for this
29
lack of robustness, the authors propose a subsample feasible qausi-GLS (FQGLS) test
that has correct asymptotic size even in the presence of nuisance parameters. This
differs from many of the above tests, which use Bonferroni-type tests that are known
to be conservative.
3.3.2 Predictability in the presence of model instability and uncertainty
This literature is vast and complex. In this section, we focus only on areas that have
seen recent econometric developments or are seen as emerging areas. We begin by
looking at model instability, focusing on studies that have developed the predictability
framework under the assumption of structural break uncertainty (see e.g. Pesaran and
Timmermann, 1995, 2002). We also review another group of studies that treat
structural breaks as being deterministic in nature and, hence, address issues
surrounding the number and duration of breaks. Related to this is the idea that there is
a stochastic process underlying the structural breaks that is used to predict future
structural breaks. The time-varying literature takes the issue of model instability to the
extreme, and is premised on the notion that there are not just one, two, or five
structural breaks, but many structural breaks across each period that render parameter
uncertainty. To this end, this literature argues for time-varying approaches for
estimating parameters, and developing many tests to both detect the phenomenon and
to develop such approaches. Furthermore, choosing the right set of variables for
forecasting has led to some studies trying to deal with model uncertainty. Finally,
there are those we refer to as ‘hybrid studies’ within the literature on model instability
and uncertainty that address aspects of instability and uncertainty within the same
predictability framework.
30
3.3.3 Model instability
(a) Structural break uncertainty
Structural breaks refer to both permanent shifts and ‘breaks’ (temporary jumps) in the
parameters of the return generating process. There could be various reasons for
permanent shifts, including legislative, institutional or technological changes, shifts in
economic policy, or even large macroeconomic shocks such as the doubling or
quadrupling of oil prices that have been experienced over recent decades (Pesaran et
al., 2006). Breaks (or jumps) in the parameters may also arise due to a number of
factors, including major changes in market sentiment, the creation or bursting of
speculative bubbles, or regime switches that affect monetary and debt management
policies. The latter, for example, might include switches from money supply targeting
to inflation targeting, or from short-term to long-term debt instruments (Pesaran and
Timmermann, 2002).
To address parameter instability, many studies are concerned with the problem of
determining in real time how much historical information to use when estimating a
forecasting model. Studies use a range of methods, such as a rolling window of
observations with a fixed size to generate the forecast, discounted least squares that
assigns smaller weights to observations further away from the point of the prediction,
or recursive least squares that allows for expansion of the observation window to
allow for new information (see Pesaran and Timmermann, 2002). While Pesaran and
Timmermann (1995) allow the forecasting model to change over time, they do
mention in their 2002 paper that this may be inappropriate in the presence of breaks in
the parameters of the forecasting model. The choice of estimation window of a
forecasting model is endogenised in Cooper and Gulen (1999), but that study is
31
constrained to either rolling windows of fixed length or an expanding window.
However, none of these methods explicitly detect, and condition on, the occurrence of
one or several breaks. This is a concern of Pesaran and Timmermann (2002), who
develop a conditionally time-varying window size using a two-stage approach. A
reversed ordered Cusum (ROC) test is developed to detect the most recent breakpoint.
This test is related to the standard CUSUM test developed by Brown et al. (1975) (see
Tian and Anderson, 2014, for a detailed discussion). When adopted recursively
through time, the reversed ordered Cusum procedure yields a sequence of estimation
windows whose lengths effectively indicate the ‘memory’ of the return model under
consideration. The resulting sequence of ROC tests statistics is used to choose and
forecast from a single post-break estimation window.
(b) Deterministic structural breaks
There are studies that treat structural breaks as being deterministic in nature. The aim
of these studies is to explicitly identify the number and duration of break dates, and to
examine the influence of the structural breaks in the forecasting exercise. As implied
above, the identification of the number and duration of the structural breaks or regime
shifts is critical here. Early studies determined the number and duration of structural
breaks exogenously. However, given the uncertainty with this approach, various
studies have attempted to develop techniques that allow determination of the breaks
endogenously (see e.g. Rapach and Wohar, 2006).
The Chow (1960) procedure is a familiar test with the null hypothesis of no structural
change, but one may use the standard F-test to test this against the alternative only if
the breakpoint is known. Quandt (1960) suggests using the maximum F-statistic over
all values of break dates as a means to test parameter stability. This search over a set
32
of dependent F-statistics affects the asymptotic distribution of the test, which ceases
to be χ2 (Elliott & Müller, 2003). Expanding on Quandt (1960), Andrews (1993)
derives the limiting distribution of the supremum of the Fk statistics (SupF statistic),
which is nonstandard and dependent on a trimming parameter. At any given trimming
parameter, the null hypothesis of no structural break can be tested using the
asymptotic critical values in Andrews (1993) and, if the null is rejected, the break date
can be estimated (see also Rapach and Wohar, 2006). Hansen (2000) develops a
heteroskedastic fixed-regressor bootstrap procedure that delivers the correct
asymptotic distribution for the SupF statistic in the presence of general
nonstationarities in the regressors, including mean and variance breaks and unit roots,
which Andrew’s asymptotic distribution fails to account for. Bai (1997), and Bai and
Perron (1998, 2003a, 2004) explicitly test for multiple structural breaks at unknown
dates in the bivariate predictive regression models. Apart from allowing for multiple
breaks, the Bai and Perron methodology accounts for autocorrelation in the regression
model residuals, heteroskedasticity in the residuals, and different moment matrices for
the regressors in the different regimes when computing test statistics and confidence
intervals for the break dates and regression coefficients.
(c) Stochastic structural breaks in forecasting
Pesaran et al. (2006) develop a test to examine how future values of the variables of
interest might be affected by multiple breaks. As the authors explain, this question
cannot treat structural breaks as deterministic (as in the case of past structural breaks)
unless they are known; rather, it requires a modelling of the stochastic process
underlying the breaks. They propose a Bayesian estimation and prediction procedure
that allows for the possibility of new breaks occurring over the forecast horizon,
taking into account the size and duration of past breaks (if any) by means of a
33
hierarchical hidden Markov chain model. Here, predictions form by integrating
parameters from the meta-distribution that characterizes the stochastic break-point
process.
(d) Time-varying parameter - parameter uncertainty
In the stock market predictability literature, various studies, including Paye and
Timmermann (2006), and Goyal and Welch (2008), show that the magnitude of asset
return predictability is distinctly time-varying and unstable; however, this is not just
limited to stock returns but is true of a wide range of time series (see Stock and
Watson, 1996). Merton’s (1973) intertemporal CAPM also suggests that time-varying
risk aversion can lead to a time-varying relationship between stock returns and
predictive variables (see Zhu and Zhu, 2013). And if predictability of returns partly
reflects market inefficiencies and not just time-varying risk premia, then predictive
relationships should disappear once discovered, provided that sufficient capital is
allocated towards exploiting them (Pesaran and Timmermann, 2002). Several studies
show the importance of business cycles in dealing with predictability in returns (see
e.g. Fama and French, 1989; Lettau and Ludvigson, 2001; Cooper and Priestly, 2009;
Henkel et al., 2011; Nitschka, 2013, 2014). Collectively, these studies make the point
that parameter uncertainty or the time varying nature of parameters seem to be driven
by business cycles.
While the studies on structural breaks/jump work mainly with one to five breaks, the
time-varying parameter literature is concerned with large as well as small parameter
changes that occur now and then. Furthermore, because the breaking process can
occur in any number of ways – for instance, over the review period, breaks can occur
34
every year or every second year, in clusters, or randomly – several studies have
focused on different breaking processes. To give a flavour, studies such as Shively
(1988b) work with Gaussian breaks of constant variance every period, Andrea and
Ploberger (1994) use a finite number of breaks by employing an average asymptotic,
and Bai and Perron (1998, 2003) work with the maximum of a sequence of F-statistics
for their power criterion. To compare various breaking processes used in the model
instability and time-varying parameter literature, Elliott and Müller (2003), in
particular, show that leaving the exact breaking process unspecified (apart from a
scaling parameter) does not result in a loss of power, at least asymptotically.
Here, as explained by Hackl and Westlund (1989), time-varying studies are concerned
with tests to detect non-constant parameters in regressions and, if the null of constant
regression is rejected, implement time varying approaches. A number of studies
examine the hypothesis of constant regression against the alternative hypothesis that
the parameter is stochastic and follows a first order autoregressive process – in this
case, the non-constant parameter is modelled to deviate only temporarily from zero,
so that the ’long-run’ value remains the estimated parameter (see Shively, 1988a).
Most Markov switching models with recurring states and threshold autoregressive
models are also closely related to the case of a stable autoregressive process for the
non-constant parameter (see also Elliott and Müller, 2003). Most studies in this area,
however, consider models in which deviations of the non-constant parameter from
zero are permanent. In these models the alternative hypothesis is that the non-constant
parameter follows a random walk. For the ‘unobserved components’ model, see
Chernoff and Zacks (1964), and Nyblom and Mäkeläinen (1983). For more general
35
models, see Garbade (1977), LaMotte and McWhorter (1978), Franzini and Harvey
(1983), Nabeya and Tanaka (1988), or Leybourne and McCabe (1989).
(e) Model uncertainty
Similarly, while some predictive variables such as financial ratios, including dividend
yields and price-earnings ratios, are popular in the predictability literature, many other
predictability variables are also covered.2 Given the high volume of predictors, it
might often seem unclear to an investor as to which set of variables comprises the
correct predictive variables (see also Schrimpf, 2010). Hence, an important question
that arises is how investors choose between so many competing models (Pesaran and
Timmermann, 2002). Moreover, choosing the best model or model thinning is
restrictive, as information from the discarded models is ignored in each period (Aiolfi
and Favero, 2005). Beginning with Cremers (2002), and Avramov (2002), studies
examine ways to efficiently deal with this model uncertainty. As Aiolri and Favero
(2005) explain, a natural way to interpret model uncertainty is to refrain from the
assumption of the existence of a ‘true’ model and instead attach probabilities to
different possible models – an approach known as ‘Bayesian model averaging’.
Cremers (2002), and Avramov (2002) use a pure Bayesian model averaging approach
that requires prior elicitation for the relevant parameters, conditional on the different
models. Avramov (2002) applies an empirical Bayesian approach for prior elicitation,
which uses data-information from the sample for prior elicitation. However, such an
2 Among others, predictors of equities in the literature include expected inflation (Bodie, 1976; Fama,
1981), short-term interest rates (Fama and Schwert, 1977; Hodrick, 1992), output gap (Cooper and
Priestly, 2009; Møller et al., 2014); the consumption wealth ratio (Lettau and Ludvigson, 2001);
consumer confidence (Møller et al., 2014); and investor sentiments/attention/anchoring behaviours (Li
and Yu, 2012). The fact that many variables have been found to be valuable predictors of returns has
raised concern that apparent predictability may be a result of data-snooping rather than of genuine
variation in economic risk-premia (see e.g. Goyal and Welch, 2008). Authors such as Schrimpf (2010),
Cremers (2002), and Avramov (2002) regard the long list of apparent predictive variables as a sign of
model uncertainty.
36
approach has been criticized for using information about the dependent variable,
which violates the rules of probability necessary for conditioning (Fernández et al.,
2001). In the Bayesian tradition, Cremers (2002) specifies subjective prior
distributions that are based on different beliefs about predictability. The specification
of prior beliefs, however, can be a problematic task when the set of models becomes
very large (Schrimpf, 2010). To avoid the drawback of the dependence on prior
distribution, studies such as Schrimpf (2010) adopt the Salai-Martin et al. (2004)
approach, that is, the Bayesian averaging of classical estimates. Furthermore, a pure
Bayesian model averaging approach takes all predictive variables as exogenous. To
remedy this, Schrimpf (2010) combines the Bayesian feature of model averaging with
coefficients estimated by standard OLS, which are adjusted for endogeneity bias
following Amihud and Hurvich (2004), and Amihud et al. (2009).
3.3.4 Combination forecasts
The pioneering work of Bates and Granger (1969) suggests that if a number of
unbiased forecasts of the same future variable are available, then, rather than using
one, the forecasts can always be combined in such a way that the composite forecast
has variance less than or equal to any of the competing forecasts. Since Bates and
Granger’s (1969) work, various ‘model averaging’ studies have tested the efficacy of
combination forecasts from different models (similar to Bates and Granger, 1969).
While there is clear support for combination forecasts in this literature, it is not
obvious which combination scheme is the best. Bates and Granger (1969) find that
combination forecasts that allow the weights to change can lead to better forecasts
than those that result from the application of a constant weight determined after
noting all individual forecast errors. Makridakis and Winkler (1983) show that
37
differential weights that are proportional to the reciprocal of a sum of squared errors
work better than a simple average.
Recent studies have resorted to combining models using either the same or different
estimation procedure but different predictors. Examples include shrinkage methods
such as ridge regression (Hoerl and Kennard, 1970), bootstrap aggregation (or
bagging) (Breiman, 1996), and the least absolute shrinkage and selection operator
(Lasso) (Tibshirani, 1996). These studies apply various flexible weighting to
individual predictors and include: bagging (Breiman, 1996), which applies differential
shrinkage weights to each coefficient; adaptive Lasso (Zou, 2006), which applies
variable-specific weights to the individual predictors in a data-dependent adaptive
manner; the elastic net (Zou and Hastie, 2005; Zou and Zhang, 2009), which
introduces extra parameters to control for the penalty of including additional
variables; and Bayesian methods such as adaptive Monte Carlo (Lamnisos et al.,
2012; Tian and Anderson, 2014), which assign heavier weights to forecasts that use
more recent information on different estimation windows. Elliot et al. (2013) show
that combinations of subset regressions can produce more accurate forecasts than
conventional approaches based on equal-weighted forecasts, combinations of
univariate forecasts, or forecasts generated by methods such as bagging, ridge
regression or Bayesian model averaging.
While combination forecasting is becoming popular in the economics literature,
predictability literature in finance is only just beginning to catch up (see Rapach et al.,
2010). Only a few methods have been developed/applied in the finance literature. For
instance, a fixed number of predictors of stock returns are combined using an equal-
38
weighted scheme on the basis of complete subset regressions (Elliot et al., 2013),
averaging of OLS and Kalman filter of Mamaysky et al. (2008) models of mutual
funds (Mamaysky et al., 2007), equal-weighted methods to combine many univariate
equity premium models (Rapach et al., 2010), and equal-weighted combinations of
forecasts of stock returns from all possible two variable models (Aiolfi and Favero,
2003).
Overall, the strong message in recent studies is that combination forecasting is better
than standalone forecasting. And while it is unclear which combination method is the
best, a scheme that applies differential weights seems to work well in this literature.
Moreover, it appears using a few schemes is the best approach.
3.4 State of the art
3.4.1 Persistence
At present, Bonferroni-type procedures are regarded as the state-of-the-art in this
literature, but they do have some properties that limit their adoption in empirical work
(Phillip and Lee, 2013). Other alternatives are available, including Phillip and Lee’s
(2013) parametric test and Kasparis et al.’s (2014) non-parametric test. Both tests can
be easily applied and are versatile enough to accommodate a wide range of predictors,
including stationary as well as non-stationary fractional and near unit root processes.
3.4.2 Persistence, endogeneity and heterogeneity
Modeling approaches that take account of endogeneity, heterogeneity and persistence
and can be implemented easily are state-of-the-art. Westerlund and Narayan (2014b)
(one predictor) and Lewellen (2004) (multiple predictors) are two approaches for time
series analysis, while Westerlund and Narayan (2014a) present a panel-based test.
39
3.4.3 Model instability and uncertainty
There are several standalone developments in this literature that have made significant
contributions. Methods that will make the most difference include those that
incorporate several features of model instability and uncertainty. For instance, using
Bayesian model averaging techniques, Pettenuzzo and Timmermann (2011) account
for model uncertainty and instability; that is, investors are not assumed to know the
true model or its parameter values, nor are they assumed to know the number, timing
or magnitude of past or future breaks. Instead, they come with prior beliefs about the
meta-distribution from which current and future values of the parameters of the return
model are drawn and update these beliefs efficiently as new data are observed.
Zhu and Zhu (2013), on the other hand, develop a Bayesian regime-switching
combination (BRSC) approach that explicitly incorporates model, regime and
parameter uncertainty to examine the out-of-sample return forecasting problem. Here
they incorporate model uncertainty, as in Barberis (2000), and Cremers (2002). The
uncertainty about parameters is summarized by the posterior distribution of the
parameters given by the data. Instead of constructing the distribution of expected
returns conditional on fixed parameter estimates, the Bayesian method integrates over
the uncertainty in the parameters captured by the posterior distribution. To account for
time varying predictability and address the regime uncertainty issue, the regime-
switching combination approach is used (see Rapach et al., 2010) to account for
model uncertainty and efficiently use the information contained in a large collection
of candidate predictive variables.
40
3.4.4 Combination forecasts
With many models and predictors of securities and exchange rates, this is one
important area of research. However, it is difficult to suggest state-of the art
techniques here, as many developments in this area have occurred outside the
financial econometrics literature that currently relies heavily on equal-weighted
forecasts from two to many univariate models of returns or equity premium or model
averaging schemes. A recent paper by Elliot et al., (2013) shows that combinations of
subset regressions can produce more accurate forecasts of stock returns than
conventional approaches based on equal-weighted forecasts, combinations of
univariate forecasts, or forecasts generated by methods such as bagging, ridge
regression or Bayesian model averaging.
3.5 Suggestions for future research
This survey highlights that econometric developments in predictability mainly address
challenges in modeling predictability one or two at a time. It is likely that future
research will provide more hybrid approaches that address several if not all
forecasting challenges simultaneously, and which can be easily implemented
empirically. There is a glimpse of this gradually starting to occur in some of the most
recent literature. For example, as mentioned above, Pettenuzzo and Timmermann
(2011) address model uncertainty and instability, Zhu and Zhu (2013), address model,
regime and parameter uncertainty, and Westerlund and Narayan, (2014a, 2014b)
address persistence, endogeneity and heterskedasticity. However, with the exception
of a few models, the performance of hybrid models set against each other as well as
against standard approaches is mostly unknown. Future research into robustly
evaluating such models is necessary to determine which model provides more
41
accurate results. Focusing on just the three studies mentioned above, Westerland and
Narayan (2014a, 2014b) models might be further extended to cater for time-varying
parameters and model uncertainty as in Pettenuzzo and Timmerman (2011) to derive
more fine-tuned results. Hence, a mixture of strategies that include data and model
features, and model and parameter uncertainty may possibly lead to more superior
models. However, for these innovations to occur, it is likely that financial
econometric research will need to embrace more of the literature on combination
methods, which is a large and growing area of research on its own.
4. Conclusion
The purpose of this paper has been to review econometric developments in the areas
of price discovery and price predictability. We have focused on these two topics
because they are conceptually linked. Both areas have benefited from similar
developments in econometric modelling and, in contrast with areas such as
ARCH/GARCH and stochastic volatility, have not been reviewed before.
In terms of the current status of the two literatures, both areas are informed by
developments in modelling of unit roots, cointegration and VAR/VECM processes.
While this is most evident in the price discovery literature, it is also reflected in the
price predictability literature in terms of, for example, addressing persistence and
modelling predictability on the presence of instability and uncertainty. Both literatures
essentially follow two directions. One is to develop new methods based on relaxing
the assumptions of time series models. Examples include allowing for fractionally
integrated/cointegrated processes, addressing non-linearities, and accommodating
structural breaks and parameter instability. The other is to develop panel-based
models to harness the extra power of cross-sectional and time series information. In
both literatures, it is difficult to pinpoint the exact state-of-the-art. It very much
42
depends on the extension/feature one wants to focus on, which, in turn, dictates the
assumption(s) one wants to relax. There are few methods dealing with either topic
that simultaneously address several issues at once.
In terms of looking forward, this survey suggests several directions. The first flows
from evidence that the financial econometric applications in price discovery and price
predictability, as well as in other areas of finance, are being fuelled by developments
within econometrics itself. Indeed, many of the recent empirical applications in price
discovery and price predictability are on the frontier of econometric methods. Given
this, further developments in econometric modelling are needed to relax the
assumptions and push the boundaries of applications to price discovery and price
predictability.
Second, a limitation of both the price discovery and price predictability literatures is
that there has largely been a piecemeal approach in which econometric issues have
been dealt with on a one-by-one basis. This reflects the manner in which the
econometrics literature has evolved. An area for future research, then, is to develop
new modelling methods that combine/synthesise recent developments across multiple
econometric issues and address more than one issue at once. One obvious way to
begin this is through integrating developments in the time series literature into panel-
based frameworks.
A third direction is to take a step back and reconsider what insights from recent
developments in econometric modelling that challenge stylised facts tell us about
long-held beliefs on the apparent empirical regularities in price discovery and price
predictability. For example, in the price discovery literature, allowing for fractional
43
integration and time-varying dynamics is challenging previous findings about whether
price discovery occurs in spot or futures markets, as well as the role of fundamental
factors in driving prices in financial crises. This opens up the opportunity to develop
theory to explain these empirical results.
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