Typically, in education and psychology research, the investigator collects data and subsequently performs descriptive and inferential statistics. For example, a researcher might compute group means and use the null hypothesis significance testing procedure to draw conclusions about the populations from which the groups were drawn. We propose an alternative inferential statistical procedure that is performed prior to data collection rather than afterwards. To use this procedure, the researcher specifies how close she or he desires the group means to be to their corresponding population means and how confident she or he wishes to be that this actually is so. We derive an equation that provides researchers with a way to determine the sample size needed to meet the specifications concerning closeness and confidence, regardless of the number of groups.