Fisher Exact Test

Graham Tall   G.E.Tall@bham.ac.uk

Uses categorical (nominal/head count) data and is directly equivalent to two-way chi-square  with  2 groups and 2 categories.   The calculation of probability is better than that with chi-square because Fisher Exact Test calculates the exact probability of obtaining the result obtained by chance.  Statistics books generally recommend that it be used when the total number in the category table is 20 or less, in such circumstances SPSS calculates it automatically:

Chi-square. For tables with two rows and two columns, select Chi-square to calculate the Pearson chi-square, the likelihood-ratio chi-square, Fisher’s exact test, and Yates’ corrected chi-square (continuity correction).  For 2 x 2 tables, Fisher’s exact test is computed when a table that does not result from missing rows or columns in a larger table has a cell with an expected frequency of less than 5. Yates’ corrected chi-square is computed for all other 2 x 2 tables.   (My underlining)

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