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The spurious precision of GDP

22 February 2012 By Edward Hadas

An American, a Frenchman and a physicist were talking about some unusual weather. “It was twice as hot this afternoon as this morning”, said the American, “the temperature went up from 40 to 80 degrees.” The Frenchman interjected: “That’s in Fahrenheit. In Celsius, it was six times hotter.” The physicist was scornful. “On the only really scientific measure, the Kelvin scale, the increase was a piffling 5 percent.”

Who’s right? Well, all the measures are accurate and it certainly was hotter. But no single ratio – whether twice, six times or 5 percent – captures just how much hotter it actually felt. The feeling of hotness, like the feelings of pain or anger, cannot be measured with genuine precision.

It is the same for the feeling of prosperity – any measure will be arbitrary and quite possibly misleading. Consider gross domestic product, the most common index of economic success. GDP is the sum of spending on everything in the economy, from shoes to shoe-shines, from cars to child care. In comparing countries with each other or over time, GDP is usually adjusted for inflation to calculate what is ambitiously called “real GDP”. It is then often divided by the population, creating “real GDP per person”. This is usually measured in “constant dollars” and, for 2011 in the United States, becomes $43,149 of 2005 dollars.

Economists recognise that GDP is far from perfect. In 2009, a French government commission suggested that it should be augmented by measures of the distribution of wealth, environmental sustainability and “quality of life”. The Human Development Index, which is widely used by the United Nations, combines GDP with life expectancy and years of schooling.

These modifications are welcome, but they fail to correct GDP’s main weakness – that is what might be called the fallacy of precision. The human meaning of prosperity simply cannot be reduced to numbers. Supposedly exact measures generally confuse more than they illuminate.

My rejection of quantification is anathema to most economists, who fancy themselves to be hard scientists. It also goes against utilitarianism, economists’ favourite philosophy, which claims all decisions can be reduced to numerical comparisons.

But consider an example: real GDP per person in the United States is up 103 percent since 1971. That sounds basically right: overall, Americans are substantially richer than they were four decades ago. The improvements include a 12 percent increase in life expectancy at birth, the shift from clunky black-and-white to sleek colour television and the introduction of the Internet into more than 70 percent of households. The gains far outweigh the losses, such as a 26 percent fall in the number of highway miles per resident.

The exact number, though, is a fiction. There is no way to assign a weight to each of the gains and losses, and no reason to assume that GDP, which measures the inflation-adjusted price of the various goods and services, is a particularly meaningful summation.

Happiness economists try to dodge the problem by looking for a measurable and meaningful number in people’s feelings. They claim subjective satisfaction can be counted up, simply by asking people to rate their happiness on a scale of, say, 1 to 5. The approach has many problems, one of which is that it doesn’t make any sense to say happiness has increased by, say, 12 percent.

Emotions just don’t work that way. George may love his current girlfriend more than his ex, but it’s only a figure of speech to say he loves her twice as much. Similarly, it makes no sense to say we are twice as happy as our parents or 12 percent happier than we were a half a decade ago.

GDP and similar measures can be quite helpful rough indicators, especially for poor countries. For example, the Chinese government aims at 8 percent annual real GDP increase – that rate creates jobs without putting excessive strain on society. But the authorities in Beijing should be careful, for the precision is spurious. Sometime soon, the right GDP growth number will be lower. And when China gets rich enough, no measure of wealth will provide much insight.

Look at the International Monetary Fund’s calculation that GDP per person was 27 percent lower in France than in the United States in 2011. The exactitude is ridiculous and the basic conclusion, that Americans are substantially richer than French people, is silly. The countries are both rich and modern, just in somewhat different, incommensurate ways. France has cheaper medical care, longer holidays and better mass transit and bakeries. The United States has bigger houses and more cars per person.

Numbers are seductive, so economists, politicians and pundits tend to fret over every tenth of a percentage point of GDP. But it is easy to exaggerate the importance of incremental changes in measures of this sort. It would be better to stop striving for precision. Or at least to cut back by 92.4 percent.


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