The higher limits, after all, were thought to be a way to solve the problem of how to get Americans to put away more money for retirement. But the study’s results indicate the increased limits didn’t result in a statistically significant improvement among the majority of workers. People who previously hadn’t approached the limits didn’t increase their contributions in a statistically significant way.

Instead, the new limits mostly affected less than 10 percent of workers: people who were in higher income brackets with more disposable income, who would have saved more early on if they could have and were prevented from doing so by existing limits. This group took advantage of the tax incentives offered along with the higher limits and increased their 401(k) contributions, with people over 50 doing so at a greater rate than those under 50 and availing themselves of the benefits of the catch-up contribution.

On the other hand, those who never approached the earlier contribution limits didn’t substantially increase the amount they saved.

The study also found that it was questionable whether those higher-income older workers who substantially increased their 401(k) savings increased their savings overall, or simply moved money from one form of savings to another in order to take advantage of the tax benefit offered by the higher contribution limits.