[R] Sample size calculation proportions with EpiR: Discrepancy to other calculators

Karl Knoblick karlknoblich at yahoo.de
Tue May 26 08:53:37 CEST 2009


I have done a sample size calculation for proportions with EpiR. The input is:
treatment group rate p=0.65
control group rate p=0.50
significance level 0.95
power 0.80
ration group 1 and 2: 1.0

I have done this in the following way:
epi.studysize(treat = 0.65, control = 0.5, n = NA, sigma = NA, power = 0.80,
   r = 1, conf.level = 0.95, sided.test = 2, method = "proportions")

[1] 82

PASS 2002 and NQuery give both 170 subjects per group without continuity correction. With continuity correction 183 per group.

Looking at http://statpages.org/proppowr.html I get 182 subjects per group (with continuity correction, I admit).

What am I doing wrong? Can anybody explain this?

Best wishes

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