Bill, You might want to start with the following reference: Cohen, J. (1992). A power primer. Psychological Bulletin, 112, 155-159. J Joaquin Borrego, Jr., Ph.D. Assistant Professor Department of Psychology PO Box 42051 Texas Tech University Lubbock, TX 79409-2051 (806) 742-3711 ext 232 (O) (806) 742-0818 (Fax) email: joaquin.borrego@ttu.edu Web site: http://webpages.acs.ttu.edu/joborreg