[Rd] (no subject)

From: fang lai <laifang1_at_yahoo.com>
Date: Sun 31 Oct 2004 - 18:17:58 EST


Dear all,
 I have several questions regarding fisher.test() in R, and I'd highly appreciate any help with it.  I have a group of observations, each having people's income, and an indicator of whether selected in or out a program. I want to test the difference between income of people who are in and out.
 Because the distribution is far from normal, I decide to use the fisher's exact test, using either mean or rank as statistics.
 Question 0 is: Can I do this test using fisher.test() in R?
If so,
 My first question is: Does fisher.test() offer an option to choose the statistics? Actually it is not clear from the help to me what statistics it uses. Does it just compare the mean of people in and out of the program?
 My second question is: when the group is large, I always receive a warning message such as "Fisher exact result might not be right" when I set "hybrid=T". When I set "hybrid=F", it does return a result of p-value without warning message. I wonder if this p-value is reliable or not. And, how does it get the approximation of p-value when "hybrid=F"? Ideally, it should randomly draw, say 1000 times, from the full sets of permutation of assignment, and get an approximate p-value--is this the way it works in fisher.test( ) in R? If not, does it use another test, or some other measure of approximation?
 My last question is: when the group is small enough, will it calculates the exact probabilities even if hybrid=F?
Many thanks,

Fang



Lai, Fang

PhD candidate
University of California, Berkeley
Department of Agricultural and Resource Economics 314 Giannini Hall, Berkeley, CA 94720-3310

tel: (510) 643 - 5421(O)
     (510) 847 - 9811(Cell)
fax: (510) 643 - 8911

email: lai@are.berkeley.edu
http://www.are.berkeley.edu/jobmarket/fang.html

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https://stat.ethz.ch/mailman/listinfo/r-devel Received on Sun Oct 31 18:36:42 2004

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