Compare the mean of a continuous measurement in two samples. This calculator shows detectable effect size given sample 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.
The standard normal deviate for α = Zα =
The standard normal deviate for β = Zβ =
Sample size including cluster correction:
Treatment group size = N'1 =
Control group size = N'0 =
Size of combined group = N'total =
Design effect = 1 + (ρ(m-1)) =
Functional sample size (i.e., excluding cluster correction):
Treatment group size = N1 = N'1/Design effect (rounded) =
Control group size = N0 = N'0/Design effect (rounded) =
Size of combined group = Ntotal =
Proportion of total in treatment group = q1 =
Proportion of total in control group = q0 =
A = 1/q1 + 1/q0 =
B = (Zα + Zβ)2 =
Detectable effect size = E = S√AB/N =
Donner A, Birkett N, Buck C. Randomization by cluster. Sample size requirements and analysis. Am J Epidemiol 1981;114:906-14.