Changes in Social Security rules between 1992 and 2004 led to more men aged 65 to 67 staying in full-time work and increasing their labor force participation. These changes encouraged delaying retirement, returning to work after retiring, and partial retirement. The study found that these rule changes accounted for about one sixth of the increase in labor force participation for married men in their mid-60s. However, the decrease in labor force participation for men in their fifties during this period was not due to Social Security changes, but possibly other factors like disability.