1. Module Interpreting Real Gross Domestic Product11
KRUGMAN'S
MACROECONOMICS for AP*
Margaret Ray and David Anderson

2. What you will learn in this Module:
The difference between real GDP and nominal GDP
Why real GDP is the appropriate measure of real economic activity

3. What GDP Tells Us Economic Size Comparison
When we hear a report of the latest Gross Domestic Product, we are hearing the value of current production at the current prices.
Valuing 2009 production with 2009 prices creates nominal GDP in 2009.
This is also known as current-dollar GDP or “money” GDP.
This is used to gauge the size of the macroeconomy because it does value the total output of final goods and services over that period of time.
This measure is often compared across nations. If the GDP in the US is twice the size of the GDP of another country, we often say that our economy is twice as big.
As we will see, this can be misleading.
Note: The instructor can help to make this point by showing the class a table of recent years of US nominal GDP (a 5-year span of the 2000’s) and then show a table of GDP for a 5-year span in the 1980s. Bring this table back when you are ready to calculate real GDP.
Relative size of country indicates
relative size of Gross Domestic
Product

4. Real GDP: A Measure of Aggergate Output
Inflation’s effect on GDP
Aggregate Output
GDP is really a P*Q measure. You take the quantity of output (Q) and multiply by the price of the output (P). If prices rise, and Q stays the same, GDP will increase. This is misleading because the true size of the economy hasn’t increased, it has just gotten more expensive.
To adjust for changing prices, we create Real GDP, which calculates the value of current production, but using prices from a fixed point in time.
This fixed point in time is called the base year.
Valuing 2009 production at 2008 prices creates real GDP in 2009 and allows us to compare it back to 2008 (the base year).
This is also known as constant-dollar GDP.
Note: The instructor can now show the real GDP numbers for the same years from the table of nominal GDP numbers. Explain which year is the base year. Then show how the real size of the economy has changed from the 1980s to recent years.

5. Calculating Real GDP Year Tons of Corn Price per Ton Tons of Soybeans
Nominal GDP
Real GDP Base Year = 2007
2007
100
$100 80
$50
(100*$100) + (80*$50) = $14,000
$14,000
2008
110
$110
(110*$110) + (80*$50) = $20,100
(110*$100) + (80* $50) = $15,000
Suppose an economy consists of only two commodities. The table above shows prices and output levels for two recent years.
Note: The instructor might want to select two goods/services that are relevant to the local community or state.
Nominal GDP in each year multiplies current prices by current levels of output.
In this simple economy, nominal GDP has risen by $6100.
In % terms: (20,100 – 14,000)/14,000 = .436 or 43.6%
WOW! The politicians will really be proud of themselves!!!
But was this increase due to a fundamental increase in output, or was it due to higher prices?
Let’s hold prices constant at 2007 levels and compute the value of real GDP.
By choosing to use 2007 prices, we have made 2007 our base year.
Notice that nominal GDP = real GDP in the base year of 2007.
Now we compute real GDP in 2008 by using output in 2008, but at prices from 2007.
Real GDP 2008 = $15,000, so in real terms the value of the economic output has only risen by $1000
In % terms: (15,000 – 14,000)/14,000 = .071 or 7.1%
Note: The instructor could add a third year where real GDP actually falls and introduce the class to what it means when the data indicates a recession.

6. What Real GDP Doesn’t Measure
Real GDP v. GDP per capita
Living Standards
Limitations of Real GDP per capita
Note: Stress to the students that GDP, and real GDP, are just statistical measures. They are positive, not normative. They should not be used to measure a nation’s self-esteem, or sense of overall happiness.
Many of the things that make people happy do not contribute to this statistic.
Taking time off from work to coach your child’s soccer team. Volunteerism detracts from GDP.
Many forms of leisure do not contribute to GDP. Read a book, take a walk, play catch with your child and you are hurting the economy.
Work around the house. If you rake your own leaves, rather than hire a company to do it, you detract from GDP. If you decided to drop out of the labor force to help raise kids, you detract from GDP.
Some things that contribute to GDP don’t make us happier.
Spending money to put bars in your windows because your neighborhood is unsafe will add to GDP.
Likewise, imagine two economies. One is based upon the buying/producing of assault rifles and one is based upon the buying/producing of ice cream. Both will add to GDP, but which is “better”?
Cleaning up after a natural disaster (Katrina, or a snow storm) will add to GDP.
Spending money to fight preventable diseases (emphysema) will add to GDP.