THE big investment shift of recent years is from active to passive. Clients have been buying index funds, which passively track a benchmark like the S&P 500 index, and shunning fund managers who actively try to pick the best shares.

One reason for the shift is that passive managers charge lower fees than active funds. Many clients would be happy to pay more if that translated into better performance. However, it is very difficult for investors to select fund managers who can reliably beat their peers. Performance does not persist, as the latest data from S&P Dow Jones Indices show clearly.

Suppose you had picked one of the best-performing 25% of American equity mutual funds in the 12 months to March 2013. In the subsequent 12 months, to March 2014, only 25.6% of those funds stayed in the top quartile (see chart). That result is no better than chance. In the subsequent 12-month periods, this elite bunch is winnowed down to 4.1%, 0.5% and 0.3%—all figures that are worse than...Continue reading