Two calculators for two-group survival analysis.
Calculator 1: Number of events, given relative hazard.
Instructions: Enter parameters in the green cells. Answers will appear in the blue box below.
α (two-tailed) =
Threshold probability for rejecting the null hypothesis. Type I error rate.
β =
Probability of failing to reject the null hypothesis under the alternative hypothesis. Type II error rate.
q1 =
Proportion of subjects that are in Group 1 (exposed)
q0 =
0.7
Proportion of subjects that are in Group 0 (unexposed); 1-q1
RH =
Relative hazard (Group 1/Group 0)
The standard normal deviate for α = Zα =
The standard normal deviate for β = Zβ =
A = (Zα+Zβ)2 =
B = (log(RH))2q0q1 =
Total events needed = A/B =
Calculator 2: Sample size, given number of events.
This calculator will calculate the number of subjects needed in each group to achieve the number of events calculated above.
Note: If you change the default values for EITHER BER0 or ST0 below, the calculator will automatically update the other parameter accordingly.
q1 =
q0 =
RH =
Total events =
BER0 =
Baseline Event Rate (events/unit time) for Group 0
ST0 =
Median survival time in Group 0
CR =
Censoring rate - censored/unit time (assumed equal for both groups)
FU =
Planned average length of follow-up, in time units
Sample size (with continuity correction)
|
N |
Events |
Cumulative Event Rate |
| Group 1 |
|
|
|
| Group 0 |
|
|
|
| Total |
|
|
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Schoenfeld DA. Sample-size formula for the proportional-hazards regression model. Biometrics 1983;39:499-503.