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

[Chuck Cleland]

On 5/26/2009 2:53 AM, Karl Knoblick wrote:
> Hallo!
> 
> 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
> two-sided
> ration group 1 and 2: 1.0
> 
> I have done this in the following way:
> library(epiR)
> 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")
> 
> Result: 
> $n
> [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? 

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
> Karl
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> 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.
NDRI, Inc. (www.ndri.org)
71 West 23rd Street, 8th floor
New York, NY 10010
tel: (212) 845-4495 (Tu, Th)
tel: (732) 512-0171 (M, W, F)
fax: (917) 438-0894