A Computer Program for Fisher's Exact Probability Test

Abstract

The Fisher test is concerned with data of independent groups and a dichotomous criterion in a fourfold (2 × 2) contingency format. Typically, small samples (N ≤ 30) are considered. Some tables of critical values of Fisher's test for small samples are available to offset the tediousness of computation. Fisher's test requires determination of a combined probability, that is, the observed set added with all the more extreme (directional) sets. For large samples, an approximation method such as chi square is used. Considered in this paper are a mathematical discussion and algorithm, and a computer program for Fisher's test. The computer program for small and large (N of about 500) samples is available from the authors. Such technology, in most instances, makes approximation methods unnecessary.

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References

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Tritchler, D. L. and Pedrini, D. T. Fishept: A computer program for Fisher's exact probability test. Unpublished manuscript, University of Nebraska at Omaha, 1975.