Garry - Unless the use of commands -tabi- and -csi- have changed, it appears
that you discovered something wrong in Stata 8. In Stata 7, one gets correct
results, both for -tabi- and -csi-:
Al Feiveson
==================================================================
[Stata 7]
. tabi 3 0 \ 0 3
| col
row | 1 2 | Total
-----------+----------------------+----------
1 | 3 0 | 3
2 | 0 3 | 3
-----------+----------------------+----------
Total | 3 3 | 6
Fisher's exact = 0.100
1-sided Fisher's exact = 0.050
. csi 3 0 0 3,e
| Exposed Unexposed | Total
-----------------+------------------------+----------
Cases | 3 0 | 3
Noncases | 0 3 | 3
-----------------+------------------------+----------
Total | 3 3 | 6
| |
Risk | 1 0 | .5
| |
| Point estimate | [95% Conf. Interval]
|------------------------+----------------------
Risk difference | 1 | 1 1
Risk ratio | . | . .
Attr. frac. ex. | 1 | . .
Attr. frac. pop | 1 |
+-----------------------------------------------
1-sided Fisher's exact P = 0.0500
2-sided Fisher's exact P = 0.1000
=====================================================================.
Stata 8:
. csi 3 0 0 3,e
| Exposed Unexposed | Total
-----------------+------------------------+----------
Cases | 3 0 | 3
Noncases | 0 3 | 3
-----------------+------------------------+----------
Total | 3 3 | 6
| |
Risk | 1 0 | .5
| |
| Point estimate | [95% Conf. Interval]
|------------------------+----------------------
Risk difference | 1 | 1 1
Risk ratio | . | . .
Attr. frac. ex. | 1 | . .
Attr. frac. pop | 1 |
+-----------------------------------------------
1-sided Fisher's exact P = 0.0000
2-sided Fisher's exact P = 0.0000
. tabi 3 0 \ 0 3
| col
row | 1 2 | Total
-----------+----------------------+----------
1 | 3 0 | 3
2 | 0 3 | 3
-----------+----------------------+----------
Total | 3 3 | 6
Fisher's exact = 0.000
1-sided Fisher's exact = 0.000
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Garry Anderson
Sent: Wednesday, March 17, 2004 4:38 AM
To: [email protected]
Subject: st: Fisher's exact P and -csi-
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: [email protected]
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