Statalist The Stata Listserver

[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

Re: st: fishers exact test

From   Marcello Pagano <>
Subject   Re: st: fishers exact test
Date   Tue, 28 Feb 2006 14:48:41 -0500

No problem.  It is saying that all tables that satisfy
these marginal constraints are as likely or less
likely than the table you have observed, within
round-off.  Round-off also explains the

A better name than exact, since it rarely is, would
be something like permutation.

m.p. wrote:


I have a 2x2 table:

first row: 41 12
second row: 6 1

Running tabi gives a p-value for Fisher's exact test of 1.0 (two sided) and
0.52 (one sided). The hypothesis suggests using two sided value.

A reviewer commented that p-values, unless the data is quite unique, should
not be 1.0

Why is the p-value for Fisher's exact test exactly 1.0? Does this make
Moreover, after viewing "return list," the p-value isn't 1.0 but
1.00000000012. How can a p-value exceed 1.0?

Also, looking on the web, some sites calculate the following:

Two sided p-values for p(O>=E|O<=E)
p-value= 1.0000000000* (the sum of small p's)
Two sided p-value for p(O>E|O<E)
p-value= 0.6385656450 (the sum of small p's)

Should I be using a different test?

Thank you,
Richard Lenhardt

*   For searches and help try:

© Copyright 1996–2017 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index