Thanks for the answers. Does anybody have more examples than in the help of epiR? After the experience of "proportion" and "cohort" I am somehow uncertain.
Karl ----- Ursprüngliche Mail ---- Von: Thomas Lumley <tlum...@u.washington.edu> An: Chuck Cleland <cclel...@optonline.net> CC: Karl Knoblick <karlknobl...@yahoo.de>; r-h...@stat.math.ethz.ch Gesendet: Dienstag, den 26. Mai 2009, 16:43:09 Uhr Betreff: Re: [R] Sample size calculation proportions with EpiR: Discrepancy to other calculators On Tue, 26 May 2009, Chuck Cleland wrote: > 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). > And simulation confirms that the larger numbers are correct. I don't know what is happening with epi.studysize(,method="proportion"). epi.studysize(,method="cohort") doesn't seem exactly appropriate, since judging from the example on the help page the inputs are supposed to be cumulative incidence rather than probabilities. -thomas Thomas Lumley Assoc. Professor, Biostatistics tlum...@u.washington.edu University of Washington, Seattle ______________________________________________ R-help@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.
