[R] Sample size calculation proportions with EpiR: Discrepancy to other calculators
ccleland at optonline.net
Tue May 26 10:56:22 CEST 2009
On 5/26/2009 2:53 AM, Karl Knoblick wrote:
> 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")
>  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?
epi.studysize(treat = .65, control = .50, n = NA, sigma = NA,
power = 0.80, r = 1, conf.level = 0.95, sided.test = 2, method = "cohort")
gives the same sample size as PASS 2002 and NQuery (170 per group).
> Best wishes
> R-help at r-project.org mailing list
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
Chuck Cleland, Ph.D.
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