Survival Analysis · COX-CONT

Sample Size for Cox Regression with a Continuous Predictor

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

1. Planning setup

Effect-entry mode

The hazard ratio applies to the predictor increment entered below.

2. Information obtained from previous study / literature

Hazard ratio for stated increment

Predictor increment, ΔX

Predictor standard deviation

Expected target-event proportion (%)

Predictor-covariate R² (%)

This is the covariate-correlation adjustment, not the Cox model’s outcome R².

3. Information decided by the researcher

Alternative

Significance level, alpha

Power (%)

Anticipated dropout/non-response (%)

4. Results

Enter assumptions and select Calculate.

Formula, assumptions, limitations, and methodological note

Example clinical scenario

A cancer cohort study tests whether baseline tumour size, entered as a continuous predictor, is associated with the hazard of recurrence.

Formula and methodological note

Uses the Hsieh–Lavori asymptotic Cox proportional-hazards approximation for one primary continuous predictor.

Not for prediction development, nonlinear or spline effects, dichotomised predictors, interactions, time-varying effects, non-proportional hazards, competing risks, recurrent events, clustered data, or variable selection.

Method references

Hsieh FY, Lavori PW. Sample-size calculations for the Cox proportional hazards regression model with nonbinary covariates. Control Clin Trials. 2000;21:552–560.
Schoenfeld DA. Sample-size formula for the proportional-hazards regression model. Biometrics. 1983;39:499–503.
Cox DR. Regression models and life-tables. J R Stat Soc Series B Stat Methodol. 1972;34:187–220.
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 Continuous Predictor (COX-CONT).” Web calculator. NajibMY, 2026. Accessed July 29, 2026. https://najibmy.netlify.app/tools/sample-size/survival-analysis/cox-regression-continuous-predictor/.