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Clinical Trials · PAR-EQ-C

Sample Size for an Equivalence Trial with a Continuous Outcome

Use this calculator to plan a two-arm parallel equivalence trial with a continuous outcome when clinically acceptable differences are defined by symmetric 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 mean reduction in systolic blood pressure between a generic medicine and its reference product and is designed to show that the difference lies within equivalence 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. 3.13.

Suggested citation

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