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Clinical Trials · XO-SUP-C

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

Use this calculator to plan a two-treatment, two-period AB/BA crossover superiority trial with a continuous primary outcome using the variability of the within-participant treatment difference.

1. Planning setup

Outcome direction

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

SD of the complete YT − YR difference; do not enter a marginal treatment SD.

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 stable asthma receive both inhalers in an AB/BA crossover trial designed to show a superior mean lung-function response with the experimental inhaler.

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. Continuous planning uses the SD of complete within-participant treatment differences, not a marginal treatment SD.

Method references

  1. Chow SC, Shao J, Wang H, Lokhnygina Y. Sample Size Calculations in Clinical Research. 3rd ed. CRC Press; 2018. Eq. 3.17.

Suggested citation

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