Slides

The study planning needed to achieve various study sizes, and an understanding of statistical power that a given study size can yield, are important aspects in the design of randomized controlled trials (RCTs). Reporting on the rationale underlying the size of treatment arms is clearly specified in the Consolidated Standards of Reporting Trials (CONSORT) and Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guidelines, and institutional review boards often require such statements in a study protocol before data collection can begin. The rationale for study size in an RCT usually depends on calculations of the study size needed to achieve a specified level of statistical power for the primary hypothesis under study, defined as the probability of rejecting the null hypothesis when an alternative hypothesis is true. Several software packages and online tools exist for performing these calculations, and textbooks give more detail on the calculations for a wide variety of data structures and statistical models.