Sample Size: X-Sectional, Cohort, & Randomized Clinical Trials

Two-sided significance level(1-alpha):

95

Power(1-beta, % chance of detecting):

80

Ratio of sample size, Unexposed/Exposed:

1

Percent of Unexposed with Outcome:

15

Percent of Exposed with Outcome:

5.5

Odds Ratio:

0.32

Risk/Prevalence Ratio:

0.36

Risk/Prevalence difference:

−9.8

Kelsey

Fleiss

Fleiss with CC

Sample Size-Exposed

151

150

170

Sample Size-Nonexposed

151

150

170

Total sample size:

302

300

340

References

Kelsey et al., Methods in Observational Epidemiology 2nd Edition, Tables 12-15

Fleiss, Statistical Methods for Rates and Proportions, Formulas 3.18 & 3.19

CC = Continuity Correction

Results are rounded up to the nearest integer