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Clinical Trials · PAR-EQ-B

Sample Size for an Equivalence Trial with a Binary Outcome

Use this calculator to plan a two-arm equivalence trial with a binary outcome when clinically acceptable differences are defined by symmetric absolute risk-difference limits.

1. Planning setup

Enter 1 for equal allocation, 2 for 2:1, or 0.5 for 1:2.

2. Information obtained from previous study / literature

3. Information decided by the researcher

4. Results

Enter the trial assumptions and select Calculate.

Formula, assumptions, limitations, and methodological note

Example clinical scenario

A randomized trial compares clinical-response proportions for a generic treatment and its reference product and is designed to show equivalence within prespecified margins.

Formula and methodological note

This calculator uses the specified Chow et al. large-sample normal-approximation method for two independent parallel groups. It assumes the planned allocation ratio, no clustering or pairing, and no covariate adjustment. It does not implement exact, score-based, Farrington–Manning, crossover, repeated-measures, or cluster-trial methods.

The equivalence calculation uses a conservative symmetric-margin formula. With a 5% alpha for each one-sided test, its confidence-interval interpretation uses a 90% two-sided confidence interval.

Method references

  1. Chow SC, Shao J, Wang H, Lokhnygina Y. Sample Size Calculations in Clinical Research. 3rd ed. CRC Press; 2018. Eq. 4.9.

Suggested citation

Yaacob, Najib Majdi. “Sample Size for an Equivalence Trial with a Binary Outcome (PAR-EQ-B).” Web calculator. NajibMY, 2026. Accessed July 29, 2026. http://127.0.0.1:4321/tools/sample-size/clinical-complex-study-designs/equivalence-binary-outcome/.