Comedy is all about timing. The same can be said of the private-equity business -- which has failed to produce many smiles for investors over the past year.

History shows that the best-performing buyout funds are those that invest during recessionary cycles, when valuations are lowest. The worst performers are typically those invested after a long run of strong economic growth, when valuations are highest.

It looks as if the deal makers at Apollo Management are demonstrating this private-equity syndrome in spades. The firm has generated some of its best results during weak economic ...