Planning significant and meaningful research in exercise science: estimating sample size.

Exercise science researchers are familiar with the use of parametric tests to detect significant differences among treatment groups. However, in planning research a question asked with increasing frequency is, "How many participants are needed to detect real and meaningful differences among groups?" In this paper, we provide an overview of the use of alpha, power, and effect size in planning sample sizes that allow tests of real and meaningful differences among groups. Because effect size is the parameter most often missing, we have located meta-analyses in sport and exercise psychology (n = 26), and motor behavior (n = 6). We provide examples and a discussion of how researchers can use these effect sizes along with common estimates of alpha and power to plan for the sample size needed to detect real and meaningful group differences.