Some Practical Guidelines for Effective Sample Size Determination

TLDR

Sample size determination is a critical yet challenging step in statistical study planning, requiring accurate estimates of error variances and meaningful effect sizes while avoiding common shortcuts. This article provides practical recommendations for effective sample size determination and emphasizes that the ultimate goal is to design a high‑quality study rather than merely meeting a numeric target. The authors critique ill‑advised shortcuts in power and sample size calculations, highlighting their potential pitfalls.

Abstract

Sample size determination is often an important step in planning a statistical study—and it is usually a difficult one. Among the important hurdles to be surpassed, one must obtain an estimate of one or more error variances and specify an effect size of importance. There is the temptation to take some shortcuts. This article offers some suggestions for successful and meaningful sample size determination. Also discussed is the possibility that sample size may not be the main issue, that the real goal is to design a high-quality study. Finally, criticism is made of some ill-advised shortcuts relating to power and sample size.