Many men in the U.S. leave the labor force when their earnings decline compared with their better-paid peers, new research shows. The study found that more men drop out when when workers' relative earnings fall.

The findings, from the Federal Reserve of Boston, help explain a trend economists have been puzzling over for decades: Why so many men have given up on the idea of holding down a job. Roughly one in nine men ages 25 to 54, an individual's prime working years, are out of the labor market today; that compared to one in 50 in the mid-1950s.

The trend has been driven chiefly by working-age men without college degrees who are exiting the labor force at higher rates, according to the study. Since 1980, workers without a four-year college degree have seen their earnings steadily erode relative to their college-educated peers, the findings show.

Over the course of the 40-year study period, earnings for prime-age men without a degree fell 17%, while college-educated mages wages rose 20%, the study's author, economist Pinghui Wu, wrote.

Along with examining the impact of earnings, the study takes into account the economic security and social status that jobs also provide. The findings suggest that men who saw their social status and earning power erode over time may have lost their incentive to work.

"For many workers, a job not only offers financial security, it also affirms their status, which is tied to their position relative to their age peers and many social outcomes," Wu wrote.

Other economists have theorized that the decline in manufacturing jobs chased men out of the labor force. But sectors like manufacturing and construction have been adding jobs steadily.