Below are worked examples that provide an overview of models and illustrate how the results are calculated once you click "Calculate Results" 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 four worked examples reflect the four primary variations that are addressed in the IRGT sample size calculator: fully nested simple difference; fully nested net difference; partially nested simple difference, and; partially nested net difference.
Separately, users make selections for the: Type I error rate; power; expected distribution of the primary outcome; intraclass correlation; number of groups or clusters in one or both arms, number of members per group or cluster, and – for partially nested designs – the number of members or participants measured in the control condition; expected benefit, if any, from regression adjustment for covariates; and magnitude of the intervention effect.
The following documents provide the formula for the detectable difference for four variations and walk 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.
Fully Nested
- Example based on an analysis of a simple difference (PDF)
- Example based on an analysis of a net difference (PDF)
Partially Nested
- 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.