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Clinical Trials · XO-SUP-B

Sample Size for a 2×2 Crossover Superiority Trial with a Binary Outcome

Use this calculator to plan a two-treatment, two-period AB/BA crossover superiority trial with a binary outcome using anticipated discordant paired-response probabilities.

1. Planning setup

Interpretation of outcome = 1

This calculator assumes equal allocation to sequences AB and BA in a two-treatment, two-period crossover trial.

2. Information obtained from previous study / literature

Discordant paired probability.

The two discordant probabilities must sum to no more than 100%.

3. Information decided by the researcher

Enter 0 for conventional superiority versus no difference.

4. Results

Enter the crossover-trial assumptions and select Calculate.

Formula, assumptions, limitations, and methodological note

Example clinical scenario

Patients with recurrent migraine receive both treatments in an AB/BA crossover trial that compares paired headache-relief responses to demonstrate superiority.

Formula and methodological note

This calculator uses the Chow et al. large-sample normal approximation for a standard two-treatment, two-period AB/BA crossover design with equal sequence sizes. It assumes adequate washout, a stable condition, no clinically meaningful carryover, and complete paired treatment outcomes for analysable participants.

It does not estimate or correct for period, sequence, or carryover effects, and does not apply to replicated, cluster, multi-period, or multi-treatment crossover designs. Binary planning uses discordant paired probabilities, not independent marginal group rates.

Method references

  1. Chow SC, Shao J, Wang H, Lokhnygina Y. Sample Size Calculations in Clinical Research. 3rd ed. CRC Press; 2018. Eq. 4.12.

Suggested citation

Yaacob, Najib Majdi. “Sample Size for a 2×2 Crossover Superiority Trial with a Binary Outcome (XO-SUP-B).” Web calculator. NajibMY, 2026. Accessed July 29, 2026. http://127.0.0.1:4321/tools/sample-size/clinical-complex-study-designs/crossover-superiority-binary-outcome/.