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. In addition, a document illustrating example calculations for the variance of continuous, dichotomous, and count outcomes is provided.
Worked Examples for Detectable Difference
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.
- Example based on an analysis of a simple difference (PDF)
- Example based on an analysis of a net difference (PDF)
Worked Examples for Outcome Variance
The distribution of the outcome – continuous, dichotomous, or count – can determine its variance. Clicking the link below will take you to a PDF that presents how outcome variance is calculated based on user inputs as well as example calculations.