Genuine power curves in forgetting: A quantitative analysis of individual subject forgetting functions

Wixted and Ebbesen (1991) showed that forgetting functions produced by a variety of procedures are often well described by the power function, at(-b), where a and b are free parameters. However, all of their analyses were based on data arithmetically averaged over subjects. R. B. Anderson and Tweney (1997) argue that the power law of forgetting may be an artifact of arithmetically averaging individual subject forgetting functions that are truly exponential in form and that geometric averaging would avoid this potential problem. We agree that researchers should always be cognizant of the possibility of averaging artifacts, but we also show that our conclusions about the form of forgetting remain unchanged (and goodness-of-fit statistics are scarcely affected by) whether arithmetic or geometric averaging is used. In addition, an analysis of individual subject forgetting functions shows that they, too, are described much better by a power function than by an exponential.