Worked Examples: Explaining the Results of the IRGT Sample Size Calculator

Below are two worked examples that illustrate how the results are calculated once you click "Submit" at the end of the seventh step (“Analysis”) of the individually randomized group-treatment (IRGT) trial sample size calculator.

The worked examples reflect the two primary variations that are addressed in the IRGT sample size calculator: analysis of a simple difference vs. analysis of a net difference.

Separately, users make selections for the: Type I error rate; power; expected distribution of the primary outcome; intraclass correlation; number of members or participants measured in the control condition, number of groups or clusters in the intervention condition, and number of members or participants per group or cluster in the intervention condition ; expected benefit, if any, from regression adjustment for covariates; and magnitude of the intervention effect.

Clicking either of the two links below will take you to a PDF that presents the formula for the detectable difference for that variation and walks you through an example showing how the detectable difference is calculated. You can open these files in any combination, save them, or print them, as they may be of help to you.

Last updated on April 8, 2021