"The results showed that the increase in 401(k) limits and introduction of catch-up provisions did not have a statistically significant effect on contributions of those workers unconstrained by the deferral limits -- both those under 50 and those over 50.... Constrained workers under age 50 contributed a statistically significant $917 more after 2001 than non-constrained contributors in the same age group. Constrained workers over age 50 -- those now eligible for the catch-up provisions -- contributed a statistically significant $1,697 more after 2001 than their non-constrained counterparts. This increase was about half of the amount by which they could have raised their contributions."