For a recent summary of this empirical debate, see William Gale, The Impact of Pensions and 401(k) Plans on  A Critical Assessment of the State of the Literature, paper presented at ERISA After 25  A Framework for Evaluating Pension Reform, Washington, D.C., September 17, 1999.
For a recent summary of the empirical debate, the book William Gale, The Impact of Pensions, should be seen.