From the New York Times:
A seemingly inexorable economic trend has changed direction in the past few years, as people who cited health reasons for not working are returning to the labor force.
The rise in the number of Americans not working because of disability was so persistent for two decades that some economists began to hypothesize that the trend would never reverse.
But perhaps it has. Since a peak almost four years ago, that number has steadily fallen, showing its largest decline — both in terms of head count and percentage — in at least the last 25 years. ...
The data shows that the decline has come almost entirely from the older half of the prime-age population (that is, people between 40 and 54). The drop has also been steeper among the less educated. The number of disabled nonparticipants without a high school diploma fell by 18 percent, versus 4 percent for those with at least a high school diploma. It has been somewhat larger among women (minus 9 percent) than men (minus 6 percent). ...One thing to keep in mind is that there are many people who believe themselves to be disabled by illness or injury who are not on Social Security disability benefits. Whatever has been going on probably has little or no connection to program developments at Social Security. There have been changes at Social Security over time but the only dramatic changes have been in backlogs.