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Macroeconomics, Masaryk University
Spring 2017
Lecture 2: Measuring the Cost of Living
Nikoloz Kudashvili
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Seventh Edition
Macroeconomics
Principles of
N. Gregory Mankiw
CHAPTER
11
Measuring the
Cost of Living
WojciechGerson(1831-1901)
In this chapter,
look for the answers to these questions
• What is the Consumer Price Index (CPI)?
How is it calculated? What’s it used for?
• What are the problems with the CPI? How
serious are they?
• How does the CPI differ from the GDP deflator?
• How can we use the CPI to compare dollar
amounts from different years? Why would we
want to do this, anyway?
• How can we correct interest rates for inflation?
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3
The Consumer Price Index (CPI)
 measures the typical consumer’s cost of living
 the basis of cost of living adjustments (COLAs)
in many contracts and in Social Security
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4
How the CPI Is Calculated
1. Fix the “basket.”
The Bureau of Labor Statistics (BLS) surveys
consumers to determine what’s in the typical
consumer’s “shopping basket.”
2. Find the prices.
The BLS collects data on the prices of all the
goods in the basket.
3. Compute the basket’s cost.
Use the prices to compute the total cost of the
basket.
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5
How the CPI Is Calculated
4. Choose a base year and compute the index.
The CPI in any year equals
5. Compute the inflation rate.
The percentage change in the CPI from the
preceding period.
100 x
cost of basket in current year
cost of basket in base year
CPI this year – CPI last year
CPI last year
Inflation
rate
x 100%=
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6
EXAMPLE basket: {4 pizzas, 10 lattes}
$12 x 4 + $3 x 10 = $78
$11 x 4 + $2.5 x 10 = $69
$10 x 4 + $2 x 10 = $60
cost of basket
$3.00
$2.50
$2.00
price of
latte
$122012
$112011
$102010
price of
pizza
year
Compute CPI in each year
2010: 100 x ($60/$60) = 100
2011: 100 x ($69/$60) = 115
2012: 100 x ($78/$60) = 130
Inflation rate:
15%
115 – 100
100
x 100%=
13%
130 – 115
115
x 100%=
using 2010 base year:
A C T I V E L E A R N I N G 1
Calculate the CPI
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CPI basket:
{10 lbs beef,
20 lbs chicken}
The CPI basket cost $120
in 2010, the base year.
A. Compute the CPI in 2011.
B. What was the CPI inflation rate from 2011–2012?
price
of beef
price of
chicken
2010 $4 $4
2011 $5 $5
2012 $9 $6
A C T I V E L E A R N I N G 1
Answers
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A. Compute the CPI in 2011:
Cost of CPI basket in 2011
= ($5 x 10) + ($5 x 20) = $150
CPI in 2011 = 100 x ($150/$120) = 125
CPI basket:
{10 lbs beef,
20 lbs chicken}
The CPI basket cost $120
in 2010, the base year.
price
of beef
price of
chicken
2010 $4 $4
2011 $5 $5
2012 $9 $6
A C T I V E L E A R N I N G 1
Answers
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price
of beef
price of
chicken
2010 $4 $4
2011 $5 $5
2012 $9 $6
CPI basket:
{10 lbs beef,
20 lbs chicken}
The CPI basket cost $120
in 2010, the base year.
B. What was the inflation rate from 2011–2012?
Cost of CPI basket in 2012
= ($9 x 10) + ($6 x 20) = $210
CPI in 2012 = 100 x ($210/$120) = 175
CPI inflation rate = (175 – 125)/125 = 40%
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What’s in the CPI’s Basket?
15.0%
41.0%
4.0%
17.0%
7.0%
6.0%
7.0%
3.0%
Food and bev.
Housing
Apparel
Transportation
Medical care
Recreation
Education and
communication
Other goods
and services
A C T I V E L E A R N I N G 2
Substitution bias
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CPI basket:
{10 lbs beef,
20 lbs chicken}
In 2010 and 2011,
households
bought CPI basket.
In 2012, households bought {5 lbs beef, 25 lbs chicken}.
beef chicken
cost of CPI
basket
2010 $4 $4 $120
2011 $5 $5 $150
2012 $9 $6 $210
A. Compute cost of the 2012 household basket.
B. Compute % increase in cost of household basket
over 2011–12, compare to CPI inflation rate.
A C T I V E L E A R N I N G 2
Answers
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A. Compute cost of the 2012 household basket.
($9 x 5) + ($6 x 25) = $195
CPI basket:
{10 lbs beef,
20 lbs chicken}
Household
basket in 2012:
{5 lbs beef,
25 lbs chicken}
beef chicken
cost of CPI
basket
2010 $4 $4 $120
2011 $5 $5 $150
2012 $9 $6 $210
A C T I V E L E A R N I N G 2
Answers
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B. Compute % increase in cost of household basket
over 2011–12, compare to CPI inflation rate.
Rate of increase: ($195 – $150)/$150 = 30%
CPI inflation rate from previous problem = 40%
beef chicken
cost of CPI
basket
2010 $4 $4 $120
2011 $5 $5 $150
2012 $9 $6 $210
CPI basket:
{10 lbs beef,
20 lbs chicken}
Household
basket in 2012:
{5 lbs beef,
25 lbs chicken}
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14
Problems with the CPI:
Substitution Bias
 Over time, some prices rise faster than others.
 Consumers substitute toward goods that become
relatively cheaper, mitigating the effects of price
increases.
 The CPI misses this substitution because it uses
a fixed basket of goods.
 Thus, the CPI overstates increases in the cost of
living.
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15
Problems with the CPI:
Introduction of New Goods
 The introduction of new goods increases variety,
allows consumers to find products that more
closely meet their needs.
 In effect, dollars become more valuable.
 The CPI misses this effect because it uses a
fixed basket of goods.
 Thus, the CPI overstates increases in the cost of
living.
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16
Problems with the CPI:
Unmeasured Quality Change
 Improvements in the quality of goods in the
basket increase the value of each dollar.
 The BLS tries to account for quality changes
but probably misses some, as quality is hard to
measure.
 Thus, the CPI overstates increases in the cost of
living.
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17
Problems with the CPI
 Each of these problems causes the CPI to
overstate cost of living increases.
 The BLS has made technical adjustments,
but the CPI probably still overstates inflation
by about 0.5 percent per year.
 This is important because Social Security
payments and many contracts have COLAs tied
to the CPI.
-5
0
5
10
15
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
GDP deflator CPI
Two Measures of Inflation, 1960–2013Percentchangeperyear
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19
Imported consumer goods:
 included in CPI
 excluded from GDP deflator
The basket:
 CPI uses fixed basket
 GDP deflator uses basket of
currently produced goods & services
This matters if different prices are
changing by different amounts.
Capital goods:
 excluded from CPI
 included in GDP deflator
(if produced domestically)
Contrasting the CPI and GDP Deflator
A C T I V E L E A R N I N G 3
CPI vs. GDP deflator
In each scenario, determine the effects on the
CPI and the GDP deflator.
A. Starbucks raises the price of Frappuccinos.
B. Caterpillar raises the price of the industrial
tractors it manufactures at its Illinois factory.
C. Armani raises the price of the Italian jeans it
sells in the U.S.
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A C T I V E L E A R N I N G 3
Answers
A. Starbucks raises the price of Frappuccinos.
The CPI and GDP deflator both rise.
B. Caterpillar raises the price of the industrial
tractors it manufactures at its Illinois factory.
The GDP deflator rises, the CPI does not.
C. Armani raises the price of the Italian jeans it
sells in the U.S.
The CPI rises, the GDP deflator does not.
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22
Correcting Variables for Inflation:
Comparing Dollar Figures from Different Times
 Inflation makes it harder to compare dollar
amounts from different times.
 Example: the minimum wage
 $1.25 in Dec 1963
 $7.25 in Dec 2013
 Did min wage have more purchasing power in
Dec 1963 or Dec 2013?
 To compare, use CPI to convert 1963 figure into
“2013 dollars”…
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23
 In our example,
 “year T” is 12/1963, “today” is 12/2013
 Min wage was $1.25 in year T
 CPI = 30.9 in year T, CPI = 234.6 today
Correcting Variables for Inflation:
Comparing Dollar Figures from Different Times
Amount
in today’s
dollars
Amount
in year T
dollars
Price level today
Price level in year T
= x
$9.49 $1.25
234.6
30.9
= x
The minimum wage
in 1963 was $9.49
in 2013 dollars.
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24
Correcting Variables for Inflation:
Comparing Dollar Figures from Different Times
 Researchers, business analysts, and policymakers
often use this technique to convert a time series of
current-dollar (nominal) figures into constant-dollar
(real) figures.
 They can then see how a variable has changed
over time after correcting for inflation.
 Example: the minimum wage…
$0
$2
$4
$6
$8
$10
$12
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Dollarsperhour The U.S. Minimum Wage in Current Dollars
and Today’s Dollars, 1960–2013
2013 dollars
current dollars
A C T I V E L E A R N I N G 4
Comparing tuition increases
Tuition and Fees at U.S. Colleges and Universities
1990 2013
Private non-profit 4-year $9,340 $30,094
Public 4-year $1,908 $8,893
Public 2-year $906 $3,264
CPI 130.7 232.6
Instructions: Express the 1990 tuition figures in 2013
dollars, then compute the percentage increase in real
terms for all three types of schools. Which type
experienced the largest increase in real tuition costs?
A C T I V E L E A R N I N G 4
Answers
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1990 2013 % change
CPI 130.7 232.6 78.0%
Private non-profit 4-year
(current $)
$9,340 $30,094
Private non-profit 4-year
(2010 $)
$16,622 $30,094 81.1%
Public 4-year (current $) $1,908 $8,893
Public 4-year (2010 $) $3,396 $8,893 161.9%
Public 2-year (current $) $906 $3,264
Public 2-year (2010 $) $1,612 $3,264 102.4%
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28
Correcting Variables for Inflation:
Indexation
For example, the increase in the CPI automatically
determines:
 the COLA in many multi-year labor contracts.
 adjustments in Social Security payments and
federal income tax brackets.
A dollar amount is indexed for inflation
if it is automatically corrected for inflation
by law or in a contract.
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29
Correcting Variables for Inflation:
Real vs. Nominal Interest Rates
The nominal interest rate:
 the interest rate not corrected for inflation
 the rate of growth in the dollar value of a
deposit or debt
The real interest rate:
 corrected for inflation
 the rate of growth in the purchasing power of a
deposit or debt
Real interest rate
= (nominal interest rate) – (inflation rate)
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30
Correcting Variables for Inflation:
Real vs. Nominal Interest Rates
Example:
 Deposit $1,000 for one year.
 Nominal interest rate is 9%.
 During that year, inflation is 3.5%.
 Real interest rate
= Nominal interest rate – Inflation
= 9.0% – 3.5% = 5.5%
 The purchasing power of the $1000 deposit
has grown 5.5%.
-10
-5
0
5
10
15
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Interestrate
(percentperyear)
Nominal Real
Real and Nominal Interest Rates in the U.S.,
1950–2013
Summary
• The Consumer Price Index is a measure of the
cost of living. The CPI tracks the cost of the
typical consumer’s “basket” of goods & services.
• The CPI is used to make Cost of Living
Adjustments and to correct economic variables
for the effects of inflation.
• The real interest rate is corrected for inflation
and is computed by subtracting the inflation rate
from the nominal interest rate.
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