Saved Search

Survival Analysis · COX-BIN

Sample Size for Cox Regression with a Binary Predictor

Plan target events and participants to test one prespecified binary predictor in a Cox proportional-hazards model.

1. Information obtained from previous study / literature

This adjusts for correlation between the predictor and other planned covariates; it is not the Cox model outcome R².

2. Information decided by the researcher

3. Results

Enter assumptions and select Calculate.

Formula, assumptions, limitations, and methodological note

Example clinical scenario

A cohort study tests whether biomarker-positive patients have a different hazard of cancer recurrence from biomarker-negative patients.

Formula and methodological note

Uses Schoenfeld's asymptotic Cox proportional-hazards planning approximation for one primary binary coefficient.

Not for prediction-model development, EPV rules, variable selection, interactions, time-varying effects, non-proportional hazards, competing risks, recurrent events, clusters, or more than one primary coefficient.

Method references

  1. Schoenfeld DA. Sample-size formula for the proportional-hazards regression model. Biometrics. 1983;39:499–503.
  2. Hsieh FY, Lavori PW. Sample-size calculations for the Cox proportional hazards regression model with nonbinary covariates. Control Clin Trials. 2000;21:552–560.
  3. Cox DR. Regression models and life-tables. J R Stat Soc Series B Stat Methodol. 1972;34:187–220.
  4. Schmoor C, Sauerbrei W, Schumacher M. Sample size considerations for the evaluation of prognostic factors in survival analysis. Stat Med. 2000;19:441–452.

Suggested citation

Yaacob, Najib Majdi. “Sample Size for Cox Regression with a Binary Predictor (COX-BIN).” Web calculator. NajibMY, 2026. Accessed July 29, 2026. https://najibmy.netlify.app/tools/sample-size/survival-analysis/cox-regression-binary-predictor/.