Sample Size Planning

Abstract Sample size planning is the systematic approach to selecting the number of participants to include in a research study so that some specified goal or set of goals can be satisfied with the minimum sample size. Sample size planning addresses the question, “What size sample should be used in this study?” However, an answer to an appropriate sample size question must be based on the particular goal(s) articulated by the researcher. Because of the variety of research questions that can be asked and the multiple inferences made in many studies, planning an appropriate sample size is not often straightforward. The appropriate sample size depends at least on the research questions of interest, the statistical model used, the assumptions specified in the sample size planning procedure, and the goal(s) of the study.