trailing performance tracking

William Bernstein, in his book The Intelligent Asset Allocator, provides some very striking demonstrations of the hazards of portfolio construction using trailing performance as your guide. He shows that a portfolio with allocations to each of six major asset classes that maximize the return relative to risk over the most recent five years and then held for five years consistently results in returns that are half that of a generic portfolio that is equally allocated to each of the six asset classes.

Caveat: Yeah holding for 5 years might be bad idea, MoMo guys say hold those till momentum fizzles out.