Sample Size Calculation for Cross-Sectional, Cohort, and Clinical Trials

Version 3.04.04

Two-sided significance level (α):
(Usually 0.05)
Power (1-β, % chance of detecting):
(Usually 80)
Proportion with disease in nonexposed (comparison) group:
(Between 0.0 and 1.0)

Ratio of sample size, Nonexposed / Exposed:

 (For equal samples, use 1.0)

Please fill in one of the following (leave others as zeros)

Calculated
Proportion with disease in exposed group:
(Between 0.0 and 1.0)
Odds ratio  
Risk/Prevalence Ratio  
Risk/Prevalence difference (Between -1.0 and 1.0)

  Kelsey Fleiss Fleiss with CC
 Sample Size - Exposed:

Sample Size - Nonexposed
Total sample size

Note: Kelsey et al., Methods in Observational Epidemiology, 2nd Edition, Table 12-15,and Fleiss, Statistical Methods for Rates and Proportions, formulas 3.18 & 3.19; CC = continuity correction factor.  All calculations are rounded up to the nearest integer.