Karl Knoblick
2009-May-26 06:53 UTC
[R] Sample size calculation proportions with EpiR: Discrepancy to other calculators
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? Best wishes Karl
Chuck Cleland
2009-May-26 08:56 UTC
[R] Sample size calculation proportions with EpiR: Discrepancy to other calculators
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