Compare the mean of a continuous measurement in two samples, using a z-statistic to approximate the t-statistic.

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

The standard normal deviate for α = Z_{α} =

The standard normal deviate for β = Z_{β} =

A = (1/q_{1} + 1/q_{0}) =

B = (Z_{α}+Z_{β})^{2} =

Standardized Effect Size = (E/S) =

Total group size = N = AB/(E/S)^{2} =

N_{1}:

N_{0}:

Total: 0

Because the formula used here is based on approximating the t statistic with a z statistic, it will slightly underestimate the sample size when N is less than about 30.

Reference: Hulley SB, Cummings SR, Browner WS, Grady D, Newman TB. Designing clinical research : an epidemiologic approach. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2013. Appendix 6A, page 73.