Friday’s employment report from the U.S. Department of Labor is a great reminder of how statistics can mislead—and another sign of brewing trouble for the global economy.

The U.S. economy lost 63,000 nonfarm payroll jobs in February, the largest monthly decline since March 2003. But the official unemployment rate actually fell slightly, from 4.9 percent to 4.8 percent. So is the job situation improving or worsening? And why the seemingly contradictory numbers?

The two sets of statistics come from different government surveys. But it’s not as if the payroll employment figure—which comes from a survey of business and government establishments—is somehow missing a big jump in employment captured in the unemployment rate, which comes from a survey of households. The household survey found a decrease of 255,000 employed individuals from January to February. But the unemployment rate edged down because the civilian labor force shrank by 450,000.

The civilian labor force is defined as the sum of employed and unemployed people. Sounds simple enough. But the “unemployed” category is a bit tricky: People only get counted as such if they had no employment during the reference week of the survey, they were available for work at that time and “they made specific efforts to find employment sometime during the four-week period ending with the reference week,” as the Labor Department puts it.

That means the unemployed tally excludes “discouraged workers.” They are defined as people who wanted and were available for work and had looked for a job sometime in the prior 12 months, but who hadn’t done so in the previous four weeks because they believed no jobs were available for them. There were 396,000 discouraged workers in February.

New York Times columnist David Leonhardt has an interesting column this week  saying that the employment rate of Americans in their prime years, 25 to 54 years old, has been falling, even as the unemployment rate has been declining. That means one of two things, he says: Either a growing number of people have been choosing not to work purely by their own volition, or there’s been a rise in the number of folks who aren’t working and aren’t actively looking but would like to find a good job. The latter, he says, appears to be the better explanation.

“[T]hese nonemployed workers tend to be those who have been left behind by the economic changes of the last generation,” Leonhardt writes. “Their jobs have been replaced by technology or have gone overseas, and they can no longer find work that pays as well.”

The latest U.S. employment figures not only point to a decline in consumer spending power, which bodes poorly for both the American and world economies. They also suggest Americans’ support for global trade may weaken further. Although Washington officials passed a stimulus package aimed at boosting the U.S. economy, the measure fell short of seriously strengthening the economic safety net into which many U.S. workers are falling.

Will American workers, at some point, decide that the global economy as it is set up just doesn’t work for them?