It is a familiar story across America: Since the recession, people are working again, but their jobs just aren't good enough. Often, it is because they are forced to work part-time, and their employer won't give them enough hours to make ends meet.

"What we hear in the field a lot is that people are hired with the assumption, if not promise, that they'll get full-time hours. And most weeks they don't," said Lonnie Golden, a Pennsylvania State University economics professor and author of new research published last week by the left-leaning Economic Policy Institute (EPI).

Most metrics suggest the U.S. economy has snapped back substantially since the recession. In November, the U.S. unemployment rate fell to 4.6 percent, a level not seen since August 2007. The economy has created an average of 180,000 jobs a month so far this year. But it's often the quality, not the quantity, of the jobs that is in question.

Many Americans are still cobbling together a living with one or several part-time jobs. Overall, the number of people working part-time has risen 9.1 percent from 2002 to 2016, and now totals 26.4 million, according to Golden's report. But the number of people doing "involuntary" part-time work is up 44.6 percent from 2002, to 6.4 million Americans.

A little more than 4 percent of American workers said they were involuntarily part-time in 2016 — a proportion that is down from the heights of the recession, but still elevated compared with figures before the financial crisis.

The situation is acute for low- and middle-income earners, especially women. It disproportionately affects black and Latino workers, who make up 27.9 percent of the workforce, but 41.1 percent of involuntary part-time workers.

Involuntary part-time work takes a "massive" toll on American workers, the EPI report says. Part-time jobs with unpredictable hours make it hard for workers to budget, and cut down the time they can spend with their families. These jobs often pay lower hourly wages, lack benefits such as health care or retirement savings and don't qualify for government benefits such as unemployment insurance.

While the U.S. economy looks strong by many measures, data on involuntary part-time work show what Golden refers to as the recovery's "soft underbelly." He also sees signs of a bigger structural shift in how businesses are operating, toward relying more on part-time workers to provide flexibility and cut back payrolls.

Swanson works for the Washington Post.