A reference effect approach for power analysis in fMRI.

In fMRI, the issues involved in the control of type I error are fairly well understood. In contrast, the control of type II error has received less formal attention. This is perhaps due to the fact that the consideration of type II error requires the specification of an alternative hypothesis/experimental effect. In this paper, we present a method for expressing experimental effects in fMRI in a manner relative to a reference effect. A reference effect is chosen based on its neurophysiological significance to the researcher. This method provides a means to quantitatively express alternative hypotheses for fMRI, thus allowing type II error assessment prior to the collection of fMRI data. The simultaneous control of both type I and type II error should make meaningful interpretations possible from both positive and negative fMRI results. Copyright 2001 Academic Press.