Sample size for a descriptive study of a dichotomous variable.
This calculator gives both binomial and normal approximation to the sample size.
Instructions: Enter parameters in the red cells. The answer will appear in blue below.
1. Binomial "exact" calculation:
Sample size = N =
Expected positive results in sample = x =
2. Normal approximation to the binomial calculation:
α = (1-CL)/2 =
Standard normal deviate for α = Zα =
Sample size = N = 4Zα2P(1-P)/(W2) =
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 6E, page 81.