Warning: Today's fund winners will be tomorrow's losers

Bob Olstein: Index mania misleading investors

Past performance in fact does seem to provide a good indicator of future results, just not in the way you might think.

Anyone who's ever even contemplated investing has seen the familiar disclaimer warning against picking a manager or strategy simply on track record.

A study from S&P Dow Jones Indices shows just how important heeding that advice is, finding that positive past results come close to assuring negative future results.

Specifically, of the equity mutual funds in the top quartile performance-wise—measured against their benchmark indexes—in March 2013, just 5.28 percent were still there in March 2015. The news was worse for large caps, of which just 3.95 percent managed to stay at the top.

Over three years ended in March 2015, just 16.3 percent of funds in the top half managed to stay there. The trend paints a grim picture: