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Ch. 15

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GOALS

Index Numbers

1.
2.

3.
4.
5.

Chapter 15

McGraw-Hill/Irwin

Copyright 2010 by The McGraw-Hill Companies, Inc. All rights reserved.

6.

Describe the term index.


Understand the difference between a weighted and
an unweighted index.
Construct and interpret a Laspeyres price index.
Construct and interpret a Paasche price index.
Construct and interpret a value index.
Explain how the Consumer Price Index is
constructed and interpreted.

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Index Numbers

Index Number Example 1


According to the Bureau of Labor Statistics, in January
2000 the average hourly earnings of production
workers was $13.75. In March 2008 it was $17.87.
What is the index of hourly earnings of production
workers for March 2008 based on January 2000?

INDEX NUMBER A number that measures the


relative change in price, quantity, value, or some
other item of interest from one time period to
another.

SIMPLE INDEX NUMBER measures the relative


change in just one variable.

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Index Number Example 2

Index Number Example 3


The following Excel output shows the number of passengers (in millions)
for the five largest airports in the United States in 2007.

An index can also compare one item with another.

What is the index for Atlanta, Chicago, Los Angeles, and Dallas/Ft.
Worth compared to John F. Kennedy International in New York?

Example: The population of the Canadian province of


British Columbia in 2007 was 4,352,798 and for
Ontario it was 12,753,702. What is the population
index of British Columbia compared to Ontario?

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Index Number Example 3 (cont.)

Why Convert Data to Indexes?




An index is a convenient way to express a change in a diverse


group of items.

Converting data to indexes also makes it easier to assess the


trend in a series composed of exceptionally large numbers.

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The Consumer Price Index (CPI), for example, encompasses about


400 itemsincluding golf balls, lawn mowers, hamburgers, funeral
services, and dentists fees. Prices are expressed in dollars per
pound, box, yard, and many other different units. Converting the
prices of these many diverse goods and services to one index number
allows the federal government and others concerned with inflation
keep informed of the overall movement of consumer prices.

The estimate of U.S. retail e-commerce sales for the fourth quarter of
2007, adjusted for seasonal variation, was $36,200,000 and
$30,700,000 for the fourth quarter of 2006, an increase of $5,500,000.
This increase is 18 percent, expressed as an index.

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Indexes


1.

In many situations we wish to combine several items


and develop an index to compare the cost of this
aggregation of items in two different time periods.

Different Index Numbers

2.

For example, we might be interested in an index for items that


relate to the expense of operating and maintaining an automobile.
The items in the index might include tires, oil changes, and
gasoline prices.
Or we might be interested in a college student index. This index
might include the cost of books, tuition, housing, meals, and
entertainment.

3.
4.
5.

Simple Average of the Price Indexes


Simple Aggregate Index

Weighted Indexes

There are several ways we can combine the items to


determine the index.

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Unweighted Indexes

Lespeyres Price Index


Paasche Price Index

Fishers Price Index


Value Index
Special Purpose Index

Consumer Price Index


Producer Price Index
S&P Index

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Unweighted Indexes

Laspeyres Index

Advantages Requires quantity data from only the base period. This
allows a more meaningful comparison over time. The changes in
the index can be attributed to changes in the price.
Where pt is the sum of the prices (rather than the indexes) for

Disadvantages Does not reflect changes in buying patterns over time.


Also, it may overweight goods whose prices increase.

the period t and p0 is the sum of the prices for the base period.
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Paasche Index

Simple Aggregate Index Example

Where
p is the price index
pt is the current price
p0 is the price of the base period
qt is the quantity used in the current period
q0 is the quantity used in the base period

Advantages Because it uses quantities from the current period, it


reflects current buying habits.
Disadvantages It requires quantity data for the current year. Because
different quantities are used each year, it is impossible to attribute
changes in the index to changes in price alone. It tends to
overweight the goods whose prices have declined. It requires the
prices to be recomputed each year.
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P=

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Simple Average - Example

P=
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P (100) = $14.70 (100) = 134.9


$10.90
P

Lespeyres Index - Example

P = 147.1+ ...+109.3 = 874.7 = 145.78


i

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Laspeyres Index - Example

P=

pq
p q

t 0

0 0

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(100) =

$695.72
(100) = 137.0
$507.64

Paasche Index - Example

P=
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Fishers Ideal Index




Laspeyres index tends to overweight goods whose


prices have increased. Paasches index, on the other
hand, tends to overweight goods whose prices have
gone down.

Fishers ideal index was developed in an attempt


to offset these shortcomings.

It is the geometric mean of the Laspeyres and


Paasche indexes.

p q (100) = $811.60 (100) = 135.64


$598.36
p q
t t

0 t

Fishers Ideal Index - Example


Determine Fishers ideal index for the data in Table 153.

Fisher' s ideal index = (Laspeyres ' Index)(Paa sche' s Index)


= (135.64)(137.0) = 136.24
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Value Index

Value Index - Example

A value index measures changes in both the price and


quantities involved.

A value index, such as the index of department store


sales, needs the original base-year prices, the original
base-year quantities, the present-year prices, and the
present year quantities for its construction.

Its formula is:

The prices and quantities sold at the Waleska Clothing Emporium


for various items of apparel for May 2000 and May 2005 are:

What is the index of value for May 2009 using May 2000 as the base period?
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Value Index - Example

Consumer Price Index


The U.S. Bureau of Labor Statistics reports this index monthly. It
describes the changes in prices from one period to another for a
market basket of goods and services.

V=

pq
p q

t t

0 0

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(100) =

$10,6000,000
(100) = 117.8
$9,000,000
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Producers Price Index

Dow Jones Industrial Average (DJIA)

Formerly called the Wholesale Price Index, it dates back to 1890 and is
also published by the U.S. Bureau of Labor Statistics.

It reflects the prices of over 3,400 commodities. Price data are collected
from the sellers of the commodities, and it usually refers to the first largevolume transaction for each commodity. It is a Laspeyres-type index.




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DJIA is an index of stock prices, but


perhaps it would be better to say it is
an indicator rather than an index.
It is supposed to be the mean price of
30 specific industrial stocks.
However, summing the 30 stock prices
and dividing by 30 does not calculate
its value. This is because of stock
splits, mergers, and stocks being
added or dropped.
When changes occur, adjustments are
made in the denominator used with the
average.

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CPI Uses





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It allows consumers to determine the effect of


price increases on their purchasing power.
It is a yardstick for revising wages, pensions,
alimony payments, etc.
It is an economic indicator of the rate of
inflation in the United States.
It computes real income: real income =
money income/CPI X (100)

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CPI Uses - Formulas

CPI and Real Income


CPI is used to determine real disposable personal
income, to deflate sales or other variables, to find the
purchasing power of the dollar, and to establish costof-living increases.

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CPI as a Deflator


CPI and Real Income

A price index can also be used to deflate sales or


similar money series. Deflated sales are determined
by:

The Consumer Price Index is also used to determine


the purchasing power of the dollar.

Suppose the Consumer Price Index this month is 200.0 (198284


100). What is the purchasing power of the dollar?

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