This computation, which is known as a time-weighted return, assumes something, however: a hypothetical investor who started five years ago and stayed put.

FORBES: Stampede

The five-year performance quoted above (like the ones in the tables beginning on page 136) is a time-weighted return, measuring results for a hypothetical investor who put in a sum at the beginning and stood pat.

FORBES: The fortunes of an aggressive growth fund in a bear market.