Compare the mean of a continuous measurement in two samples. This calculator determines sample size given clinically significant effect size and allows for clustered sampling. Although the t-test will be used to compare the means, this calculator approximates the t-statistic with the z-statistic.

Instructions: Enter parameters in the red cells. Answers will appear in blue below.

Step 1: Calculate sample sizes without adjustment for clustering

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 = 0.600 Proportion of subjects that are in Group 0 (unexposed); 1-q1
E = Effect size
S = Standard deviation of the outcome in the population

The standard normal deviate for α = Zα =