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Journalists, commentators, and economists often say that consumer spending makes up 70% of the U.S. economy. Indeed, it’s easy to find several examples of that claim in today’s coverage of the latest GDP data (e.g., here). And, full confession, I’ve used that phrase a few times myself.

There’s just one problem with the 70% claim: it’s wrong. Consumer spending actually makes up only 60% of the economy.

This discrepancy exists because national income accounting doesn’t always mix well with simple arithmetic. If you look at data for 2009, you will find that consumer spending totaled \$10.1 trillion, while GDP was \$14.3 trillion, both measured in current dollars. Put those together, and it appears that consumer spending is about 71% of the economy (= 10.1 / 14.3). (You get almost the exact same percentage if you do the calculation with real values, but that introduces other complexities.)

That calculation is so simple, it’s easy to understand why it has a fan club. But there’s a hidden problem. To see it, it helps to do the same calculation for other parts of the economy. Again using current dollar figures for 2009, you will find the following:

Consumer Spending 71%
Investment 12%
Government 21%
Exports 11%

Notice anything strange? If you add these four sectors of the economy together, you discover that they account for 114% of GDP. In other words, consumer spending, investment, government spending, and exports, when combined, are one-seventh larger than the total economy.

This apparent paradox—the components of the economy are bigger than the economy itself—is resolved when you consider how the economic data handle imports. In order to determine gross domestic production, the statisticians add up domestic purchases and then subtract imports. So the full national income accounts for 2009 show the following shares of the economy:

Consumer Spending 71%
Investment 12%
Government 21%
Exports 11%
Imports -14%

These figures add to 100%, as they should. They also demonstrate why consumer spending was not really 71% of the U.S. economy in 2009. Total consumer spending was indeed 71% of the size of the economy, but part of that spending went to imported goods (clothes, coffee, cars, etc.). If you want to know how much consumers contributed to U.S. GDP, you need to take the 71% figure and then deduct the portion that was spent on imports.

I am not aware of a simple way to do this calculation using the data in the regular GDP reports. Over at Mandel on Innovation and Growth, however, Michael Mandel provides a useful discussion of a paper that does this calculation for several recent years, including 2008. (Michael deserves credit for taking a leading role in fighting back against the claim that consumers are 70% of the economy.)

The paper, “Induced Consumption: Its Impact on Gross Domestic Product (GDP) and Employment” by Carl Chentrens and Art Andreassen (you can find it in this conference proceeding) makes exactly the import adjustment I described above. For 2008, it concludes that the relative shares are as follows