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Fisher's Exact Test for 2x2 Tables 
(c) Copyright March 1998 by Jianzhi Zhang and the Pennsylvania State University. Permission is granted to copy this document provided that no fee is charged for it and that this copyright notice is not removed. It is distributed free of charge by
Jianzhi Zhang
Institute of Molecular Evolutionary Genetics
Department of Biology
322 Mueller Laboratory
The Pennsylvania State University
University Park, PA 16802 USA

Current Address:

Associate Professor of Ecology

and Evolutionary Biology

University of Michigan

Ann Arbor, MI
E-mail: jianzhi@umich.edu

Jianzhi Zhang Homepage

Suggested citation
     Zhang J, Rosenberg HF, Nei M (1998) Positive Darwinian selection after gene duplication in primate ribonuclease genes. Proc. Natl. Acad. Sci. USA 95:3708-3713.
     FISHER is designed for testing independence for a 2x2 table such as 









     In other words, it answers the following question: Given two-way tables with the same fixed margin totals as the observed one, what is the chance of obtaining the observed cell frequencies a, b, c, and d and all cell frequencies that represent a greater deviation from expectation (see Sokal and Rohlf 1995). 
     First make sure that the diskette you have received contains the following files. 

fisher.c (source code) 
fisher.exe (executable file) 

     To install FISHER on your computer's hard disk drive ("C" drive given here, for example), you should create a directory where the files of this package will be present. To do this, type the following c:\md FISHER (Enter) 

     To copy the FISHER files onto your hard disk drive, insert the floppy disk containing the programs into your floppy drive ("A" drive given here, for example). Then, enter the following command c:\copy a:*.* c:\FISHER\*.* (Enter) 

     To compute the p(robability) value, type c:\FISHER\fisher 

     You will be asked to input four integers for the four cells of the 2x2 table. And the probability (p) will show up instantly. 

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