Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural...

31
Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole * and Simon Quinn January 26, 2013 Abstract This document registers testable predictions about committee voting behavior in the forthcom- ing 2013 World Schools Debating Championships. The document will be registered in the Hypothesis Registry of the Abdul Latif Jameel Poverty Action Lab (J-PAL). Testable predic- tions are recorded in Table 5 on page 13, and in Figures 1 to Figure 18 (pages 14 to 31). We will submit this document to the Hypothesis Registry today (26 January 2013), and we ask the Registry to publish on or after 6 February 2013 (the day after the Championships concludes). 1 Introduction: The randomized field experiment The World Schools Debating Championships are an annual debate tournament between high school students. Debaters are drawn from around the world to represent their countries; each nation is entitled to one team in the competition. The Championships are the premiere inter- national debate tournament for school students. This document registers predictions for judge voting behavior in the Preliminary Rounds of the 2013 Championships, to be held in Antalya, Turkey, later this month. Our predictions are formed on the basis of structural estimates using data from the previous three Championships, held in 2010, 2011 and 2012. This document outlines the structure of the Championships (including, critically, the method by which judges will be randomly assigned to committees), reports in-sample predictions for the data from 2010, 2011 and 2012, and makes out-of-sample predictions for 2013. * Department of Economics, Harvard University; [email protected]. Department of Economics, University of Oxford; [email protected]. 1

Transcript of Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural...

Page 1: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: Structural Predictions forthe 2013 World Schools Debating Championships

Tom Gole* and Simon Quinn†

January 26, 2013

Abstract

This document registers testable predictions about committee voting behavior in the forthcom-ing 2013 World Schools Debating Championships. The document will be registered in theHypothesis Registry of the Abdul Latif Jameel Poverty Action Lab (J-PAL). Testable predic-tions are recorded in Table 5 on page 13, and in Figures 1 to Figure 18 (pages 14 to 31). Wewill submit this document to the Hypothesis Registry today (26 January 2013), and we ask theRegistry to publish on or after 6 February 2013 (the day after the Championships concludes).

1 Introduction: The randomized field experiment

The World Schools Debating Championships are an annual debate tournament between high

school students. Debaters are drawn from around the world to represent their countries; each

nation is entitled to one team in the competition. The Championships are the premiere inter-

national debate tournament for school students. This document registers predictions for judge

voting behavior in the Preliminary Rounds of the 2013 Championships, to be held in Antalya,

Turkey, later this month. Our predictions are formed on the basis of structural estimates using

data from the previous three Championships, held in 2010, 2011 and 2012. This document

outlines the structure of the Championships (including, critically, the method by which judges

will be randomly assigned to committees), reports in-sample predictions for the data from

2010, 2011 and 2012, and makes out-of-sample predictions for 2013.

*Department of Economics, Harvard University; [email protected].†Department of Economics, University of Oxford; [email protected].

1

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Each debate pitches one national team against another; teams are randomly assigned to ar-

gue either for or against a controversial idea. The Championships comprise both Preliminary

Rounds and Finals Rounds. In the Preliminary Rounds, each nation competes against eight

randomly-drawn opponents. These eight debates occur across four days: Rounds 1 and 2 on

the first day, Rounds 3 and 4 on the second day, and so on. The top 16 teams then progress

to the Finals Rounds, a series of five knock-out debates culminating in the Grand Final. Our

analysis and predictions focuses exclusively on data from the Preliminary Rounds.

Judging committees: The winner of each debate is determined by a committee of three

judges. Together, this committee is required to decide which team has argued more persua-

sively. Judges assesses the debate separately, assigning points to speakers based on the cat-

egories of ‘style’, ‘content’ and ‘strategy’. A comprehensive explanation of these categories

is available at www.schoolsdebate.com. Each judge is required to complete a ballot, in

which he or she records speaker points and decides the winner of the debate; judges may not

award a tie. The debate is won by whichever team wins two or three of the judges; committee

outcomes can therefore be either ‘unanimous’ (3-0) or ‘split’ (2-1).

Judges are not allowed to communicate with each other (or with the competitors) until after

making their decisions.1 Having made their decisions, the three judges then leave the room

to confer; judges may not change their decisions after leaving the room. Having discussed

the debate together, the committee returns to the room; one judge announces the committee’s

result, and gives a brief justification for the committee’s decision. Teams and their coaches are

then encouraged to speak separately with the judges; at this point, there is a strong emphasis

on constructive feedback.

1 Judges are seated apart. There is no evidence of judges trying to ‘cheat’ by looking at each other’s notes; indeed,there are strong norms at the Championships against such behavior. Judges are also discouraged from allowing theirfacial expressions or body language to indicate their views on the debate.

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In 2013, as in 2010, 2011 and 2012, judges will be assigned to committees randomly (using a

computer), and judges will know this.2 This assignment will be subject to several constraints,

designed to improve the ‘balance’ of the randomization. Most importantly, each committee

comprised one ‘class 1’ judge (most experienced/competent), one ‘class 2’ judge and one

‘class 3’ judge (least experienced/competent). These classes will be assigned subjectively by

the tournament organizers, to ensure a balance of judging experience across different com-

mittees. Second, each committee will include at least one man and one woman, to the extent

possible.3 Third, we will limit cases of judges seeing the same team more than once in the

same tournament, and no judge will be allowed to assess his or her own team. Fourth, because

the Preliminary Rounds will be divided between different venues, we will often need to assign

pairs of judges to committees together in two debates on the same day.

Pre-tournament rankings: Teams are ranked before each tournament. On the basis of

this ranking, a random draw determines each team’s position in the draw. Pre-tournament

ranking is necessary so that each team is drawn against opponents of a range of different

qualities; i.e. so that a team does not face a disproportionate number of very strong teams in its

Preliminary Rounds, nor a disproportionate number of weaker teams. Teams are ranked on the

basis of their performance in the Preliminary Rounds of the three previous tournaments. These

rankings are public information. The pre-tournament rankings for WSDC 2013 are available

online at www.schoolsdebate.com/years/2013/2013.pre.rankings.pdf.

2 The computer code is written in Stata, and is available on request.3 In the past three tournaments, we were required to relax this constraint four times: in 2010, we allowed one all-male

committee, in 2011, we allowed two all-female committees, and in 2012, we allowed one all-male committee.

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2 Model, estimates and predictions

We model each committee as an independent Bayesian game between three players. For each

committee, we denote judge class by i ∈ {1, 2, 3}. Each player i receives a signal xi, and then

chooses whether to vote for the favorite (ai = 1) or against (ai = 0). Player i receives utility

from two mechanisms: (i) from voting for the team that (s)he prefers (where the strength of

that preference is determined by the signal xi), and (ii) from agreeing with player j and/or

with player k. We treat these mechanisms as additively separable. Note that, for example, δij

measures the utility gain for judge i from voting with judge j, and that δi measures the gain

from agreeing with both judges k and j.

Ui(ai; aj , ak, xi) =

xi + δi if ai = 1, aj = 1, ak = 1;xi + δij if ai = 1, aj = 1, ak = 0;xi + δik if ai = 1, aj = 0, ak = 1;xi if ai = 1, aj = 0, ak = 0;

0 if ai = 0, aj = 1, ak = 1;δij if ai = 0, aj = 1, ak = 0;δik if ai = 0, aj = 0, ak = 1;δi if ai = 0, aj = 0, ak = 0.

(1)

We assume that each judge weakly prefers agreement over dissent: δij , δik, δi ≥ 0.

For each committee, the distribution of signals is trivariate normal (where we assume positive

correlations, ρ12, ρ13, ρ23 > 0):4 x1x2x3

∼ N µ1

µ2µ3

,

1 ρ12 ρ13ρ12 1 ρ23ρ13 ρ23 1

. (2)

The signal xi therefore plays a dual role: it directly affects the relative utility of voting for the

favorite, and it determines the conditional expectation of the other judges’ signals:

4 Of course, as with any trivariate normal, we must also assume a positive definite covariance matrix; this impliesthe further restrictions ρ12, ρ13, ρ23 < 1 and 1 − ρ212 − ρ213 − ρ223 + 2ρ12 · ρ13 · ρ23 > 0. Note that the restrictionVar(x1) = Var(x2) = Var(x3) = 1 is made without loss of generality; if we were to parameterize these variances,all of our results would simply rescale by those new parameters. This is the same reasoning that justifies the samerestriction for the trivariate probit.

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(xjxk

) ∣∣∣∣ xi ∼ N [( µj + ρij · (xi − µi)µk + ρik · (xi − µi)

),

(1− ρ2ij ρjk − ρij · ρik

ρjk − ρij · ρik 1− ρ2ik

)].

(3)

Player i must choose a best response a∗i (xi); we limit attention to cutoff strategies: a∗i (xi) =

1 (xi ≥ x∗i ), where x∗i denotes the cutoff and 1(·) the indicator function. Player i must be

indifferent between ai = 0 and ai = 1 if xi = x∗i ; that is,

x∗i = [Pr (aj = 0, ak = 0 | xi = x∗i )− Pr (aj = 1, ak = 1 | xi = x∗i )] · δi +

[Pr (aj = 0, ak = 1 | xi = x∗i )− Pr (aj = 1, ak = 0 | xi = x∗i )] · (δij − δik) . (4)

Proposition 1 (CONDITIONAL STATE MONOTONICITY) Without loss of generality, denoteδij ≥ δik. Then, in order for player i to have a unique cutoff x∗i , it is sufficient that:5

(δij − δik − δi) <(1− ρ2ik

)ρik

·

√√√√ 2π ·(

1− ρ2ij)

1− ρ2ij − ρ2ik − ρ2jk + 2ρjk · ρij · ρik. (5)

Proof: Proofs are omitted from this document, but will be presented in an academic paper in

due course.

Proposition 2 (UNIQUE EQUILIBRIUM) It is sufficient for the existence of a unique equilib-rium that, for each judge i,

max {δi, |δij − δik|} <√

π

2(1− ω2jk)·

(√1− ρij1 + ρij

+

√1− ρik1 + ρik

)−1

, (6)

where ωjk ≡ρjk − ρij · ρik√(

1− ρ2ij)·(1− ρ2ik

) . (7)

5 Note that the restriction that the covariance matrix is positive definite is sufficient to ensure that the righthand sideof equation 5 evaluates to a real number.

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2.1 Structural implementation

Parameterization: We estimate common values for ρ12, ρ13 and ρ23 across all committees.

For each committee c, we denote the difference in pre-tournament rankings by Rc > 0. We

allow this ranking difference to shift judges’ signal means; for flexibility, we adopt a quadratic

specification, and allow a different relationship for each judge class:6

µ1c = β1 ·Rc + γ1 ·R2c ; (8)

µ2c = β2 ·Rc + γ2 ·R2c ; (9)

µ3c = β3 ·Rc + γ3 ·R2c . (10)

We use the dummy Dic to denote that judge i on committee c dissented in the previous round.

We allow this dummy to shift each judge’s preference for agreement. We allow different

classes of judges to be differentially affected by previous dissent, and we impose that each

judge is indifferent between agreeing with one peer and agreeing with two:

δ1c = δ12c = δ13c = δ1 ·D1c; (11)

δ2c = δ21c = δ23c = δ2 ·D2c; (12)

δ3c = δ31c = δ32c = δ3 ·D3c. (13)

Equations 11 – 13 show two important limitations of this estimation method. First, the current

experimental context does not allow us to identify δi, δij and δik separately; this is because the

exogenous variation (past dissent) operates at the level of the individual judge. We could use

the present structural methodology to separately identify δi, δij and δik, if we observed some

exogenous shock operating at the level of the relationship between judges i and j. Second, we

use the structural model to identify the additional preference for coordination driven by past

dissent, but we do not seek to identify the preference for coordination generally. That is, if

6 Equations 8 – 10 imply that, in the hypothetical case that two teams were equally matched (Rc = 0), then µc1 =µc2 = µc3 = 0. This is exactly as we would expect and require.

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Dic = 0, we normalize δic = 0; if Dic = 0, any preference for coordination is already proxied

by the function µic(Rc).

Constraints: We constrain the estimation so that ρ12, ρ13, ρ23 ∈ [0.01, 0.99], and so that the

covariance matrix is positive definite.7 We impose δ1, δ2, δ3 ≥ 0. Together, these constraints

ensure conditional state monotonicity (Proposition 1). Additionally, we impose the single-

equilibrium condition of Proposition 2.

Identification:

Proposition 3 (GLOBAL IDENTIFICATION OF THE THREE-PLAYER PROBIT GAME) Assume

that the conditions in Proposition 1 and Proposition 2 hold, and that Rc takes at least two

unique values. Then the structural model is globally identified.

Estimation method: The proof of identification (omitted here) will rely upon a subset of

cases on (D1c, D2c, D3c). But, to estimate efficiently, we use all of our data. Specifically, we

use Maximum Likelihood with a nested fixed-point approach. Denote the stacked parameter

vector as θ. Then, for some candidate value for θ, the inner loop solves the game for each com-

mittee c in the dataset,8 given the ranking data: (x∗1c(θ;Rc), x∗2c(θ;Rc), x

∗3c(θ;Rc)). We then

calculate the log-likelihood `(θ) using a standard triprobit structure (where we approximate

the cdf of the trivariate normal using the method of Genz (2004, ‘Numerical Computation of

Rectangular Bivariate and Trivariate Normal and t Probabilities’).9 The outer loop updates

7 That is, we additionally impose 1− ρ212 − ρ213 − ρ223 + 2ρ12 · ρ13 · ρ23 > 0.8 Note that this aspect of the problem — and the calculation of the log-likelihood — is trivially parallelizable. We

exploit this to improve dramatically the speed of estimation.9 Formally, we calculate the log-likelihood for committee c as:

`c (θ; a1c, a2c, a3c) = ln Φ3

[(2a1c − 1) ·

(β1 ·Rc + γ1 ·R2

c − x∗1(θ;Rc)),

(2a2c − 1) ·(β2 ·Rc + γ2 ·R2

c − x∗2(θ;Rc))

(2a3c − 1) ·(β3 ·Rc + γ3 ·R2

c − x∗3(θ;Rc)), ρ12, ρ23, ρ13

],

where Φ3(·) refers to the cdf of the standard trivariate normal. We treat draws of (x1, x2, x3) as independent acrosscommittees, so the sample log-likelihood is `(θ) =

∑603c=1 `c(θ).

7 Tom Gole & Simon Quinn

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using a Sequential Quadratic Program. We calculate p-values for our parameter estimates using

standard Likelihood Ratio tests.

2.2 Structural estimates

We obtain the following structural estimates.

Table 1: Structural estimates: Basic specification

PARAMETER ESTIMATE `r LR p-value

ρ12 0.725 -902.433 115.467 0.000∗∗∗

ρ13 0.526 -871.012 52.625 0.000∗∗∗

ρ23 0.542 -873.090 56.781 0.000∗∗∗

β1 0.064 -869.736 50.074 0.000∗∗∗

γ1 -6.912e−4 -847.440 5.480 0.019∗∗

β2 0.045 -855.134 20.868 0.000∗∗∗

γ2 -0.084e−4 -844.735 0.071 0.791β3 0.035 -852.373 15.346 0.000∗∗∗

γ3 0.448e−4 -844.712 0.025 0.875

δ1 0.000 -844.699 0.000 1.000δ2 0.000 -844.699 0.000 1.000δ3 0.879 -845.427 1.455 0.228

LOG-LIKELIHOOD (`u) -844.699

Confidence: ∗ p < 0.1, ∗∗ p < 0.05, ∗∗∗ p < 0.01.We calculate p-values using the the χ2 distribution with one degree of freedom. Note that, for the covariance terms,we test H0 : ρ12 = 0.01, H0 : ρ13 = 0.01 and H0 : ρ23 = 0.01; we take this approach because we use 0.01 as thelower bound on the covariance terms throughout.

8 Tom Gole & Simon Quinn

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2.3 In-sample structural predictions

We use a simulation method to make in-sample structural predictions. As explained, each

tournament involves random assignment of teams, balanced so that each team faces opponents

of a variety of different strengths. For each tournament, we take the actual structure of team

matches; this allows us to condition on the actual Rc used in each tournament, in the correct

order. We form judging committees, drawing randomly without replacement in each round.

We solve the game numerically for each committee in each tournament round, where Rc is

given by the actual Rc in the data, and (D1c, D2c, D3c) is given by each simulated judge’s

performance in the previous simulated debate. We then simulate each tournament 1000 times,

to generate a distribution of summary statistics for judge performance. (For the 2010 tourna-

ment, we truncated so that there are only 48 teams in each round; we did this by dropping the

worst-ranked teams in each round.)

Tables 2, 3 and 4 (pages 10, 11 and 12) report means and percentiles for these summary

statistics, grouped by judge class. Against each statistic, we report the statistic from the actual

data, and the corresponding percentile drawn from the Empirical CDF of the simulated data.

Together, we interpret these tables as showing that the model has a reasonably good in-sample

fit.

2.4 Out-of-sample structural predictions

We use the same method to make out-of-sample predictions for the forthcoming 2013 Cham-

pionships, where the structure of team matches is the actual structure to be used in the tourna-

ment. We provide summary statistics in Table 5 (page 13). We show the Empirical CDF for

each simulated summary statistic in Figures 1 to 18 (pages 14 to 31); these CDFs will be used

to calculate the percentiles for the actual data observed in the tournament.

9 Tom Gole & Simon Quinn

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Hypothesis Registration: The 2013 World Schools Debating ChampionshipsTa

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10 Tom Gole & Simon Quinn

Page 11: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating ChampionshipsTa

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11 Tom Gole & Simon Quinn

Page 12: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating ChampionshipsTa

ble

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12 Tom Gole & Simon Quinn

Page 13: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating ChampionshipsTa

ble

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pred

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13 Tom Gole & Simon Quinn

Page 14: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating Championships

Figu

re1:

Em

piri

calC

DF:

Pred

icte

dpr

obab

ility

that

aju

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(Cla

ss1)

14 Tom Gole & Simon Quinn

Page 15: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating Championships

Figu

re2:

Em

piri

calC

DF:

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icte

dpr

obab

ility

that

aju

dge

diss

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,con

ditio

nalo

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ving

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lass

1)

15 Tom Gole & Simon Quinn

Page 16: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating Championships

Figu

re3:

Em

piri

calC

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16 Tom Gole & Simon Quinn

Page 17: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating Championships

Figu

re4:

Em

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calC

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ility

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aju

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the

favo

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17 Tom Gole & Simon Quinn

Page 18: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating Championships

Figu

re5:

Em

piri

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(Cla

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18 Tom Gole & Simon Quinn

Page 19: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating Championships

Figu

re6:

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19 Tom Gole & Simon Quinn

Page 20: Hypothesis Registration: Structural Predictions for …...Hypothesis Registration: Structural Predictions for the 2013 World Schools Debating Championships Tom Gole* and Simon Quinn†

Hypothesis Registration: The 2013 World Schools Debating Championships

Figu

re7:

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Hypothesis Registration: The 2013 World Schools Debating Championships

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Hypothesis Registration: The 2013 World Schools Debating Championships

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Hypothesis Registration: The 2013 World Schools Debating Championships

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Hypothesis Registration: The 2013 World Schools Debating Championships

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Hypothesis Registration: The 2013 World Schools Debating Championships

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31 Tom Gole & Simon Quinn