More workers are putting off claiming Social Security benefits but the reason has little to do with the increase in the age at which full benefits are payable, a study has concluded.

Instead, it found that workers reaching the ages at which they can collect the benefits are less likely to be retired by that point than those of the past. The two main drivers were improved health that enables people to work longer overall and the shift in the private sector away from defined benefit retirement plans.

Under Social Security, the standard benefit formula applies for those who begin benefits at the “full” or “normal” retirement age. That currently is 66, after having risen from 65; it will reach age 67 for those born in 1960 or later. Benefits still can be drawn as early as age 62, although with a reduction that is now greater than it was before the full retirement age went to 66 and which will be greater still when that age rises above 66.

A study by the Center for Retirement Research found that among the first five years of the baby boomers to hit age 62, only 36.7 percent were retired by that age compared with 44 percent of those born in 1931-1941. At age 64 the difference was 49.5 vs. 53.9 percent.

Looked at another way, the average age at claiming increased by 18 months over 1996-2013.

The study concluded that as defined benefit plans “continue to fade in the private sector, claiming will likely be further delayed. If health continues to improve, claiming could be moderately delayed. The resumption of the increase in the full retirement age is not likely to lead to substantial delays in claiming.”