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st: Fisher's exact P and -csi-


From   Garry Anderson <g.anderson@unimelb.edu.au>
To   statalist@hsphsun2.harvard.edu
Subject   st: Fisher's exact P and -csi-
Date   Wed, 17 Mar 2004 21:37:36 +1100

Hi,

I am enquiring why the value of Fisher's exact P for a 2 x 2 table should decrease when there is a smaller sample size for each of the two samples and the two proportions remain at 100% and 0%?

For example
-csi 6 0 0 6,e-
1-sided Fisher's exact P = 0.0011
2-sided Fisher's exact P = 0.0022

-csi 5 0 0 5,e-
1-sided Fisher's exact P = 0.0000
2-sided Fisher's exact P = 0.0000

-csi 4 0 0 4,e-
1-sided Fisher's exact P = 0.0143
2-sided Fisher's exact P = 0.0286

-csi 3 0 0 3,e-
1-sided Fisher's exact P = 0.0000
2-sided Fisher's exact P = 0.0000

-csi 2 0 0 2,e-
1-sided Fisher's exact P = 0.0000
2-sided Fisher's exact P = 0.0000

-csi 1 0 0 1,e-
1-sided Fisher's exact P = 0.5000
2-sided Fisher's exact P = 1.0000

Any suggestions would be appreciated.

(SPSS gives P=0.1 for the 3 0 0 3 combination)

I am using Stata 8.2, 30 Jan 2004, ado 11 Mar 2004.

Kind regards, Garry

Garry Anderson
School of Veterinary Science
University of Melbourne
250 Princes Highway Ph 03 9731 2221
WERRIBEE 3030 Fax 03 9731 2388
Email: g.anderson@unimelb.edu.au
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