Olivia S. Mitchell (University of Pennsylvania, Wharton School), Stephen P. Utkus (Vanguard Center for Retirement Research) & Tongxuan (Stella) Yang (University of Pennsylvania, Wharton School) have published Turning Workers into Savers? Incentives, Liquidity, and Choice in 401(k) Plan Design, 60 Nat’l Tax J. 469 (2007).  Here is the abstract:

We use data on five hundred 401(k) pension plans to evaluate how employer matching incentives influence retirement saving. Company matches prove to have a small effect on participation and saving rates; only one in ten non–highly compensated workers joins the plan because of employer match incentives, while one–quarter fails to join even though the match offers real return premiums of up to five percent. We find that liquidity and investment constraints in 401(k) plans have negligible effects on plan saving patterns. Our research underscores the importance of default strategies to bolster pension saving including the automatic enrollment approach outlined in the 2006 Pension Protection Act and non–elective employer contributions.