Re: [R] Sample size calculation for differences between two very small proportions (Fisher's exact test or others)?

2010-11-08 Thread David Winsemius
So that a bit lower than the 77 above but implies that 42,207 would be needed. -- David. > > Thanks a lot everybody again for your suggestions, > if anybody has other comments, they are always welcome. > > Best, > > Giulio > > > > Subject: Re: [R] Sample size c

Re: [R] Sample size calculation for differences between two very small proportions (Fisher's exact test or others)?

2010-11-08 Thread Giulio Di Giovanni
ybody again for your suggestions, if anybody has other comments, they are always welcome. Best, Giulio > Subject: Re: [R] Sample size calculation for differences between two very > small proportions (Fisher's exact test or others)? > From: marc_schwa...@me.com > Date: Mon, 8 Nov

Re: [R] Sample size calculation for differences between two very small proportions (Fisher's exact test or others)?

2010-11-08 Thread Marc Schwartz
Hi, I don't have access to the article, but must presume that they are doing something "radically different" if you are "only" getting a total sample size of 20,000. Or is that 20,000 per arm? Using the G*Power app that Mitchell references below (which I have used previously, since they have a

Re: [R] Sample size calculation for differences between two very small proportions (Fisher's exact test or others)?

2010-11-08 Thread David Winsemius
On Nov 8, 2010, at 11:16 AM, Mitchell Maltenfort wrote: Not with R, Really? require(sos) findFn("power exact test") found 54 matches; retrieving 3 pages 2 3 These look on point: http://finzi.psych.upenn.edu/R/library/statmod/html/power.html http://finzi.psych.upenn.edu/R/library/binom/htm

Re: [R] Sample size calculation for differences between two very small proportions (Fisher's exact test or others)?

2010-11-08 Thread Mitchell Maltenfort
Not with R, but look for G*Power3, a free tool for power calc, includes FIsher's test. http://www.psycho.uni-duesseldorf.de/abteilungen/aap/gpower3 On Mon, Nov 8, 2010 at 10:52 AM, Giulio Di Giovanni wrote: > > > Hi, > I'm try to compute the minimum sample size needed to have at least an 80% of

[R] Sample size calculation for differences between two very small proportions (Fisher's exact test or others)?

2010-11-08 Thread Giulio Di Giovanni
Hi, I'm try to compute the minimum sample size needed to have at least an 80% of power, with alpha=0.05. The problem is that empirical proportions are really small: 0.00154 in one case and 0.00234. These are the estimated failure proportion of two medical treatments. Thomas and Conlon (1992)