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The U.S. labor market has just hit another happy landmark. Of Americans aged 25 through 54 who were neither in military uniform nor behind bars, 80.3% have jobs. That equals the January 2007 high of the last economic expansion.

This measure, also known as the prime-age employment-population ratio, or Epop, avoids a key limitation of the headline unemployment rate, which only counts people actively looking for jobs. According to the unemployment rate, the current job market is the best since the late 1960s; according to prime-age Epop, it's still not as strong as it was in 1999 and 2000.

Then again, if you go by Epop the current labor market is much, much stronger than that of the 1960s, which doesn't sound quite right. The limitation of Epop in measuring labor market conditions is that it also happens to measure societal change. Epop is so much higher now than in the 1960s because more women have joined the paid workforce. Still, that's easy enough to sort out by looking at men and women separately:

• Women's prime-age Epop is nearly back to the all-time high set in 2000; men's is still nearly three percentage points below, and more than a percentage point below the peak from the previous expansion.

• The prime-age Epop gap between men and women shrank to an all-time low in the immediate aftermath of the last recession as men lost jobs at a faster rate (the mancession). It grew again after that as men returned to work at a faster pace (the mancovery), but since 2015 it's been shrinking again.

• Men's prime-age Epop passed 95% several times in the 1950s, and hit it again in the late 1960s. As of October it was 86.5%.

To sum up: there are more than 5 million prime-age men who didn't have paid jobs in October who would have had them if 1950s/1960s conditions still prevailed and Epop was 95%.

What are they doing? The Census Bureau asks about that in the Annual Social and Economic Supplement to the Current Population Survey. In 2018, 10.4% of men aged 25 through 54 (about 6.5 million men) were not in the labor force — that is, not working for pay and not looking for a job.

Being ill or disabled is the main reason prime-age men give for not being in the labor force, and by far the biggest driver of the group's decline in labor force participation since 1991. Some of this has to do with the outdated design of the Social Security Disability Insurance program, which effectively forces disabled people to choose between leaving the labor force entirely or getting no aid at all. Eligibility changes enacted by Congress in 1984, which made it easier qualify due to hard-to-verify conditions such as chronic pain and mental illness, also enabled its increasing use as a fallback economic safety net, economist David Autor argued in a 2011 paper:

The secular decline in earnings and employment opportunities for U.S. workers with high school or lower education over the last three decades has also made SSDI an increasingly attractive option for job losers and long-term unemployed.

Over the course of the current business cycle, though, this hasn't really been that big an issue. The number of new Social Security disability awards peaked in 2010, has fallen 35% since and is now lower than at any time since 2001. The ill/disabled share of prime-age men is up only 0.1 percentage points since 2006.

There is the macabre possibility that the sharp rise in opioid deaths, with 317,000 American men dying of drug overdoses from 2007 through 2017, reduced the ill/disabled numbers. But on the whole the message from these data seems to be that the great exodus of prime-age men from work to inactivity, the subject a couple of years back of numerous reports, research papers, opinion columns (including a few by me) and at least one book, has paused or maybe even ended.

That research generally painted a picture of men with few educational credentials, and often with a criminal history, seeing so little promise in the job market that they didn't even contemplate looking for work. A 2014 poll by the Kaiser Family Foundation, CBS News and the New York Times found that 85% of jobless prime-age men did not have bachelor's degrees, and 34% had criminal records. The great crime wave of the 1970s and 1980s is long over, and the great incarceration wave that followed it is receding, so criminal records should be less prevalent going forward. Also, for the past couple of years at least, the low-credential end of the job market has been doing quite well, and even a criminal background has ceased to be the barrier it once was.

It's true that the prime-age male Epop and labor-force participation rate are still more than a percentage point lower than they were just before the last recession. But by far the biggest driver of the decline since 2006 has been men attending school. Other major contributors, especially over the longer haul, include home responsibilities and very early retirement. I'm guessing the latter is more about men who can't find good work but have spouses who can than evidence of the spectacular success of the "Fire" (financial independence, retire early) movement, but who knows. Overall, these choices don't seem to reflect economic desperation in quite the way that rising disability numbers did. They may well be signs, though, of continuing shifts in men's and women's labor market roles.

Justin Fox is a Bloomberg Opinion columnist covering business. He was the editorial director of Harvard Business Review and wrote for Time, Fortune and American Banker. He is the author of "The Myth of the Rational Market."