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 fo rmal attention. This is perhaps due to the fact that the consideration of t ype II error requires the specification of an alternative hypothesis/experi mental effect. In this paper, we present a method for expressing experiment al effects in fMRI in a manner relative to a reference effect. A reference effect is chosen based on its neurophysiological significance to the resear cher. This method provides a means to quantitatively express alternative hy potheses for fMRI, thus allowing type II error assessment prior to the coll ection of fMRI data. The simultaneous control of both type I and type II er ror should make meaningful interpretations possible from both positive and negative fMRI results. (C) 2001 Academic Press.