The U.S. economy contracted 0.2% in this year’s first quarter — or so said the Commerce Department last week.

Are the number-crunchers right? Yes. Does it matter? No one knows — and that’s a problem.

On the first point, the economists and statisticians at the Bureau of Economic Analysis know how to calculate gross domestic product. I’m sure they collect the numbers their formula needs and plug them in to the right equations.

Unfortunately, the numbers they collect and the equations they solve don’t tell us anything useful. Worse, they may actually mislead the public and policy-makers who rely on them.

Everyone thinks GDP growth is the same as economic growth. It isn’t. GDP measures national output. It worked really well in the 1950s when we had a smokestack-heavy manufacturing economy. That economy is gone and not coming back. Yet we still use its statistics to measure our prosperity, or lack thereof.

Do you drive an American car? You may think so, but it really depends how you define “American.” Some critical components of your Ford truck came from overseas. The software that makes your engine start came from cyberspace, with code written by programmers in dozens of different countries. So in what sense is your truck truly an American product?

No one can answer that question with any precision. Yet the government scores the manufacturing of that truck as American output.

It gets worse. GDP presumes all output is positive. When a tornado strikes your home and you spend $15,000 on a new roof, GDP goes up. You stimulated the economy. (Thanks!)

If you want the U.S. economy to boom, pray for “the big one” earthquake to flatten Los Angeles. Repairing that damage will create a multi-trillion boost to GDP.

Any statistic that counts natural disasters as positive obviously has serious flaws. Yet that is what GDP does. But wait, there’s more.

Suppose you work in a factory and a robot takes your job. Production goes up because, unlike you, the robot doesn’t need to sleep. It will be great news for GDP when you and the other humans get canned.

These numbers aren’t sexy or exciting, but they matter. The economy can look flat while it is really growing, or look like it is growing when it is really contracting.

The Federal Reserve, the government and private companies all use GDP to make important decisions. Bad data causes bad decisions — and those bad decisions hurt people.

Whatever GDP says, your own personal economy is the reality you have to face. Pay attention to that economy, not the one the government imagines.