Re: [R] What's the T-Value in fisher.test

From: Ted Harding <Ted.Harding_at_manchester.ac.uk>
Date: Thu, 10 Jul 2008 19:33:51 +0100 (BST)


On 10-Jul-08 16:49:57, DaveFrisch wrote:
> I do not understand how to interpret this to find the T Value
> for the data.
> Is there a way to figure this out, or another function that will
> provide this for me using Fisher's Exact Test?

If I interpret your query correctly, you are expecting to find something which corresponds to a deviation divided by its standard error (such as one gets in a t-test, as an attribute of a coefficient in a regression, etc.). The Fisher exact test does not work in these terms at all.

Essentially, with the fixed-margins assumption which underlies the Fisher exact test (of a 2x2 table), the entire table is determined by the value of one cell -- say 'a' in row 1, column 1.

Each possible value of 'a' then has a probability. The values of 'a' which give rise to an odds-ratio more distant from 1 than what is given by the value of 'a' in your data have a probability which is the sum of their individual values. This is then the P-value of the test.

That's it. There is no "T"!

Ted.

> The outcome of my data is listed below.
>
> data: DATA
> p-value = 0.1698
> alternative hypothesis: true odds ratio is not equal to 1
> 95 percent confidence interval:
> 0.6026805 79.8309210
> sample estimates:
> odds ratio
> 5.430473
> --
> View this message in context:
> http://www.nabble.com/What%27s-the-T-Value-in-fisher.test-tp18386075p183
> 86075.html
> Sent from the R help mailing list archive at Nabble.com.
>
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E-Mail: (Ted Harding) <Ted.Harding_at_manchester.ac.uk> Fax-to-email: +44 (0)870 094 0861
Date: 10-Jul-08                                       Time: 19:33:48
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