Statistics lecture 12 (chapter 12)
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Transcript of Statistics lecture 12 (chapter 12)
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• On the economic and business front many concepts can be measured directly
• When it is not possible, need to introduce an associated quantity to represent it
• Referred to as an index number
• Examples of index numbers
– Production Price Index
– Consumer Price Index
– JSE Mining, Industrial, Gold, All Share, Bond indices
– Business Confidence Index
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• A measure that summarises the change in the level of
activity, price or quantity, of a single item or a basket of
related items from one time period to another
• Expressing the value of an item in the period for which the
index is calculated as a ratio of its value in the base period
• Index is a percentage value
What is an index number?
Period of reference
relative to which an
index is calculated
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•
• When the value exceeds 100, indicates an increase in the level of activity
• When the value is less than 100, indicates a decrease in the level of activity
• Activity can indicate a change in price or quantity – Price index
– Quantity index
What is an index number? Value in period of interest
Index number = × 100Value in base period
Say: Index = 98.6
There was a:
100 – 98.6 = 1.4%
decrease
Say: Index = 108.4
There was a:
108.4 – 100 = 8.4%
increase
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• Price indices - P
– Price of the item in the period of interest – pn
– Price of the item in the base period – p0
• Quantity indices - Q
– Quantity of the item in the period of interest – qn
– Quantity of the item in the base period – q0
What is an index number?
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• Simple price index indicates the change in price of a
single item from the base period to the period under
consideration
Simple index numbers
0
100npP
p
• Simple quantity index indicates the change in quantity of a
single item from the base period to the period under
consideration
0
100nqQ
q
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• The following table indicates the prices, in rand, and
quantities (in 100) sold at a small supermarket for three years
Simple index numbers - example
2007 2008 2009
Price Quantity Price Quantity Price Quantity
Coffee (500g) 10.49 13.1 15.99 12.8 17.99 14.2
Sugar (500g) 4.99 17.3 5.29 18.7 7.49 18.2
Milk (1 l) 7.39 48.9 8.99 53.6 9.39 59.2
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• Simple price index for sugar in 2008 with 2007 as base year
Simple index numbers - example
0
5.29100 100 106.01 6.01 % increase
4.99
npP
p
2007 2008 2009
Price Quantity Price Quantity Price Quantity
Coffee (500g) 10.49 13.1 15.99 12.8 17.99 14.2
Sugar (500g) 4.99 17.3 5.29 18.7 7.49 18.2
Milk (1 l) 7.39 48.9 8.99 53.6 9.39 59.2
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• Simple quantity index for milk in 2009 with 2007 as base year
Simple index numbers - example
0
59.2100 100 121.06 21.06 % increase
48.9
nqQ
q
2007 2008 2009
Price Quantity Price Quantity Price Quantity
Coffee (500g) 10.49 13.1 15.99 12.8 17.99 14.2
Sugar (500g) 4.99 17.3 5.29 18.7 7.49 18.2
Milk (1 l) 7.39 48.9 8.99 53.6 9.39 59.2
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• Simple quantity index for sugar in 2009 with 2008 as base year
Simple index numbers - example
0
18.2100 100 97.3 2.7 % decrease
18.7
nqQ
q
2007 2008 2009
Price Quantity Price Quantity Price Quantity
Coffee (500g) 10.49 13.1 15.99 12.8 17.99 14.2
Sugar (500g) 4.99 17.3 5.29 18.7 7.49 18.2
Milk (1 l) 7.39 48.9 8.99 53.6 9.39 59.2
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Concept Questions
• 1 – 6, p418, textbook
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• Composite index reflect the average change in activity of
a basket of items from the base period to the period
under consideration
– Unweighted composite indices – all items in the
basket is considered to be of the same importance
– Weighted composite indices – each item in the basket
is weighted according to its relative importance
Composite index numbers
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• Simple composite price index
Unweighted composite index numbers
0
100np
Pp
• Simple composite quantity index
0
100nq
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• Simple composite quantity index for 2009 with 2007 as base year
Unweighted composite index numbers - example
0
14.2 18.2 59.2100 100 115.5 15.5 % inc
13.1 17.3 48.9
nqQ
q
2007 2008 2009
Price Quantity Price Quantity Price Quantity
Coffee (500g) 10.49 13.1 15.99 12.8 17.99 14.2
Sugar (500g) 4.99 17.3 5.29 18.7 7.49 18.2
Milk (1 l) 7.39 48.9 8.99 53.6 9.39 59.2
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• Simple composite price index for 2008 with 2007 as base year
Unweighted composite index numbers - example
0
15.99 5.29 8.99100 100 132.4 32.4 % inc
10.49 4.99 7.39
npP
p
2007 2008 2009
Price Quantity Price Quantity Price Quantity
Coffee (500g) 10.49 13.1 15.99 12.8 17.99 14.2
Sugar (500g) 4.99 17.3 5.29 18.7 7.49 18.2
Milk (1 l) 7.39 48.9 8.99 53.6 9.39 59.2
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• Weighted composite price index
Weighted composite index numbers
0
100np w
Pp w
• Weighted composite quantity index
0
100nq w
Qq w
Where: w = weight assigned to each item in the basket
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• Weighted composite price index for 2008 with 2007 as base year using the profit for each item as weight
Weighted composite index numbers - example
0
100
15.99(.7) 5.29(.3) 8.99(.2)100 141.3 41.3 % inc
10.49(.7) 4.99(.3) 7.39(.2)
np wP
p w
2007 2008 2009
Price Profit Price Profit Price Profit
Coffee (500g) 10.49 70% 15.99 70% 17.99 70%
Sugar (500g) 4.99 30% 5.29 30% 7.49 30%
Milk (1 l) 7.39 20% 8.99 20% 9.39 20%
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• The base period values will be assigned as weights to
the items in the basket
Weighted composite index numbers
- Laspeyres approach
• Laspeyres price index
0
0 0
100n
L
p qP
p q
• Laspeyres quantity index
0
0 0
100n
L
q pQ
q p
Price index:
weight is the quantity
in the base period
Quantity index:
weight is the price
in the base period
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• Advantage is that indices calculated for different period
using the same basket of items may be compared
directly as long as the base period remains unchanged
• Disadvantage is that it over estimates increases in the
prices as times goes by – it is necessary to adjust the
base period from time to time
Weighted composite index numbers
- Laspeyres approach
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• Laspeyres price index for 2009 with 2007 as base year
Weighted composite index numbers - example
0
0 0
17.99(13.1) 7.49(17.3) 9.39(48.9)100 100
10.49(13.1) 4.99(17.3) 7.39(48.9)
140.9 40.9 % inc
n
L
p qP
p q
2007 2008 2009
Price Quantity Price Quantity Price Quantity
Coffee (500g) 10.49 13.1 15.99 12.8 17.99 14.2
Sugar (500g) 4.99 17.3 5.29 18.7 7.49 18.2
Milk (1 l) 7.39 48.9 8.99 53.6 9.39 59.2
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• The consumed current period values will be assigned as
weights to the items in the basket
Weighted composite index numbers
- Paasche approach
• Paasche price index
0
100n n
P
n
p qP
p q
• Paasche quantity index
0
100n n
P
n
q pQ
q p
Price index:
weight is the quantity
in the current period
Quantity index:
weight is the price
in the current period
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• Advantage is that indices calculated for different period
using the same basket of items may be compared
directly as long as the base period remains unchanged
• Disadvantage is that it over estimates increases in the
prices as times goes by – it is necessary to adjust the
base period from time to time
Weighted composite index numbers
- Paasche approach
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• Paasche quantity index for 2009 with 2007 as base year
Weighted composite index numbers - example
0
14.2(17.99) 18.2(7.49) 59.2(9.39)100 100
13.1(17.99) 17.3(7.49) 48.9(9.39)
114.9 14.9 % inc
n n
P
n
q pQ
q p
2007 2008 2009
Price Quantity Price Quantity Price Quantity
Coffee (500g) 10.49 13.1 15.99 12.8 17.99 14.2
Sugar (500g) 4.99 17.3 5.29 18.7 7.49 18.2
Milk (1 l) 7.39 48.9 8.99 53.6 9.39 59.2
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• May only be used if the indices for Laspeyres and Paasche
have the same base period
Weighted composite index numbers
- Fischer approach
• Fischer price index
F L PP P P
• Fischer quantity index
F L PQ Q Q
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Example The price of bread (rands/bread), meat (rands/kg), Cabbage (rands/cabbage) and wine
(rands/bottle), as well as the quantities (in millions) consumed during 2006, 2007 & 2008
are given in the following table:-
Calculate the:-
1. Simple quantity index for meat in 2008 with 2006 as base year
2. Simple composite price index for 2007, with 2006 as base year
3. Lapeyres price index for 2008 with 2007 as base year
4. Paasche price index for 2008 with 2007 as base year
5. Fischer price index for 2008 with 2007 as base year
6. Simple composite quantity index for 2008 with 2007 as base year
7. Fischer quantity index for 2007 with 2006 as base year
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Price Quantity
2006 2007 2008 2006 2007 2008
Bread 7.0 6.6 8.4 900 1000 900
Meat 44.0 46.0 59.0 600 600 700
Cabbage 7.0 7.3 9.6 5 6 5.5
Wine 30.4 30.4 32.1 90 90 100
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EXAMPLE ANSWER
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1. 1) Q = 1000
q
qn = 100
600
700 = 116.67
2) P = 1000
p
pn = 100
4.88
3.90 = 102.15
3) PL = 10000
0
qp
qpn = 100
8.36979
6.46146 = 124.79
4) PP = 1000
n
nn
qp
qp = 100
15.41220
8.52122 = 126.45
5) PF = PL PP = )45.126)(79.124( = 125.62
6) Q = 1000
q
qn = 100
1696
5.1705 = 100.56
7) QL = 10000
0
pq
pqn = 100
35471
36178 = 101.99
QP = 1000
n
nn
pq
pq = 100
5.36312
8.36979 = 101.84
QF = PL QQ = )84.101)(99.101( = 101.92
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The index series
• Collection of indices for the same item or basket of items
constructed for a number of consecutive periods using
the same base period
• The base period will be the period = 100
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The index series - example
• Construct an index series for the monthly electricity
usage for a household – use June as base month
Month April May June July August
Useage (kw) 680 754 820 835 798
82.9 92.0 100 101.8 97.3
0
754100 100 92.0 8 % dec
820
nqQ
q
0
680100 100 82.9 17.1% dec
820
nqQ
q
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Important indices – Consumer price index • Composite price index of a representative basket of consumer goods
and services
• Serves as a measure of relative change in the prices of services and
goods consumed in SA
• Stats SA publish the CPI monthly
• Price information in the index refers to the first 7 days of that month
• Published in the second half of the next month
• Info used to determine the CPI is obtained from a survey in each of
12 urban areas for each of 3 income groups and contains almost 600
items in 17 categories
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Important indices – Consumer price index • A weight is assigned to each item in the basket according to their
relative importance
0 0
0 0
p qw
p q
0
pn
pw
CPIw
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Important indices – Consumer price index • CPI is used to determine the inflation rate
• Deflate other value series
• Adjust prices, wages, salaries and other variables for changes in the
inflation rate
• It is available quickly
• A disadvantage is that it is based on a household with on average 1.6
children, takes only certain good and services into account, includes
indirect taxes but excluded direct taxes
• Can use consecutive CPI’s as a time series to make forecasts on
future values and trends
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EXAMPLES OF IMPORTANT INDICES
• JSE all share index
• JSE gold index
• CPI- consumer price index – used to calculate
inflation rate and cost of living
• Inflation rate
• PPI – Production price index
• Business confidence index
• New car sales index
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Example
• Activity 1, p197 Module Manual
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Example
• Activity 2, p199 Module Manual
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Classwork/Homework
• Revision exercises 1,2,3 p 200 module
manual
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