Sample Size Estimation for Trials and Other Two Group Comparisons


When an investigator is designing a study to compare two groups with a continuous outcome, an essential step is the calculation of sample sizes that will allow a reasonable chance (power) of detecting a predetermined target difference (effect size), if it truly exists, at a given level of statistical significance. Four key components are required to facilitate a suitable sample size calculation. These are the target difference or effect size, the standard deviation of the outcome, and the Type I and Type II errors. This case study will illustrate the process and methods for determining the required sample size using a real case study as an example—the SELF randomized controlled trial to compare a self-managed single exercise program versus usual physiotherapy treatment for rotator cuff tendinopathy.

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