Defined benefit plans and defined contribution plans – "apples and oranges" , right? Conceptually, yes. In a defined benefit plan, it’s the employer who has to fund the promised benefit, but it’s the employee who contributes and generally invests his or her account in a defined contribution plan, e.g., 401(k).

But in the real world in which most employees who are, in fact, covered by a retirement plan, it’s 401(k) or nothing. And so the key result of a recent study, Defined Benefit vs. 401(k) Investment Returns: The 2006-2008 Update, by the consulting firm Towers Watson, has some serious implications.

The study indicates that defined benefit plans have outperformed defined contribution plans by approximately 1% a year which is consistent with their last analysis for the period 1995 and 2006.

Doesn’t sound like much, does it? But that 1% per year really matters. It can add up in terms of more lifetime retirement income. In my December 2007 blog post, What’s 1% Worth, I cited research by the investment management firm AllianceBernstein that 1% translates into about $220,000 extra at retirement—and an extra 10 years of spending as shown below:

So why the difference in defined benefit and defined contribution investment returns?

Towers Watson cites possible reasons why defined benefit plans have had better investment returns. It could be because how investment results are reported, or because of different percentages of equity exposure, or it could be that

DB plan trustees have a fiduciary responsibility for investment performance. They or the professionals they hire usually have considerable financial education, experience and access to sophisticated investment vehicles — advantages 401(k) plan participants typically lack.

So in that context, then, shouldn’t plan sponsors seriously consider a 401(k) managed account option?