Using the NIH Research Methods Resources Website.

The Research Methods Resources (RMR) section of the National Institutes of Health (NIH) website provides information on design, analysis, and sample size for designs used in NIH-supported clinical trials including randomized controlled trials, individually randomized group-treatment trials, parallel group- or cluster-randomized trials, group- or cluster-stepped wedge trials, and group regression discontinuity designs. The material provided for each design includes background information, links to webinars and training opportunities, a list of frequently asked questions and answers, the relevant CONSORT or TREND statement, key references for the designs and for state of the practice reviews, methods for sample size and power, and common errors. Sample size calculators are readily available for randomized controlled trials, but not for the other four designs; as a result, the RMR website provides a sample size calculator for each, set up as a tutorial in 8-9 steps. Each step includes text and references that can be explored if the user is new to the calculator or left largely hidden if the user is familiar with the calculator. Each sample size calculator provides worked examples for variations for the design including those based on a simple difference vs a net difference, or on a cross-sectional design vs a cohort design. The worked examples are available for download as an.pdf document and present the formulae used for the calculations. The calculators can be used to estimate sample size requirements for a new trial or to confirm a calculation made by others. The sample size calculators are illustrated with three examples.