The share of people 65 and over who are working has jumped by 50 percent in a decade and a half, the Pew Research Center reported Monday.

The figure rose from 12.8 percent of seniors on the job in May 2000 to 18.8 percent in May 2016.

Given the increase in the senior population already, the rise in the numbers of those on the job is even more dramatic: There was a surge to 9 million seniors in the labor force, up from 4 million at the start of the millennium.

The number of hours that seniors are putting in has also risen—the number of part-timers among the elderly has dropped from 46.1 percent to 36.1 percent.

The increase can also be seen when the numbers are divided into older age groups like those 75 and above.

The numbers come from a Pew analysis of Bureau of Labor Statistics data. Pew’s report looked at what was happening, but did not go into “why?”