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Sample Size Calculator (web)

Cox Regression - Rule-of-thumb

Independent variable	Scale	Categories	Count

Total independent variables count (k):
Events per variable (EPV):
Choose a value between 5 and 20 (Concato et al. 1995; Peduzzi et al. 1995; Vittinghoff & McCulloch, 2007)
Proportion with event* (p):
*Death, recurrence etc.
Expected dropout rate: %

Number of subjects with event, n₁ =
Sample size, n =
Sample size (with 10% dropout), n_drop =

References for formula:

Concato, J., Peduzzi, P., Holford, T. R., & Feinstein, A. R. (1995). Importance of events per independent variable in proportional hazards analysis I. Background, goals, and general strategy. Journal of Clinical Epidemiology, 48(12), 1495–1501.

Peduzzi, P., Concato, J., Feinstein, A. R., & Holford, T. R. (1995). Importance of events per independent variable in proportional hazards regression analysis II. Accuracy and precision of regression estimates. Journal of Clinical Epidemiology, 48(12), 1503–1510.

Vittinghoff, E., & McCulloch, C. E. (2007). Relaxing the rule of ten events per variable in logistic and Cox regression. American journal of epidemiology, 165(6), 710-718.

Suggested reference:

APA: Arifin, W. N. ( ). Sample size calculator (web). Retrieved from http://wnarifin.github.io

Vancouver: Arifin WN. Sample size calculator (web) [Internet]. [cited ]. Available from: http://wnarifin.github.io

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