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

[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/html/cloglog.sample.size.html


Would also think that methods based on a poisson model of rare events  
could be informative:

http://finzi.psych.upenn.edu/R/library/asypow/html/asypow.n.html

-- 
David.

> 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
> <perimessaggini at hotmail.com> wrote:
>>
>>
>> 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) suggested Fisher's exact test and proposed  
>> a computational method, which according to their table gives a  
>> sample size of roughly 20000. Unfortunately I cannot find any  
>> software applying their method.
>> -Does anyone know how to estimate sample size on Fisher's exact  
>> test by using R?
>> -Even better, does anybody know other, maybe optimal, methods for  
>> such a situation (small p1 and p2) and the corresponding R software?
>>
>> Thanks in advance,
>> Giulio
>>
>


David Winsemius, MD
West Hartford, CT