Suppose your observed table looks like this:
Column 1 Column 2 Total
Row 1 O11 O12 n1.
Row 2 O21 O22 n2.
Total n.1 n.2 n..
Consider the marginal totals (the n's) to be fixed. O11 is the test statistic and has a hypergeometric distribution. Think of an urn with n.1 red balls and n.2 black balls. If you randomly sample n1. balls from the urn, O11 is the number of balls in the sample that are red. Different values of O11 have different probabilities that are given by the hypergeometric distribution.
Jackie Dietz
Teresa from Oregon wrote:
I was doing a little mental calisthenics today and got myself confused about how this test is calculated. My (perhaps naive) understanding is that all potential sets of results from, say, a 2x2 table are calculated and then the exact probability of the actual observed result occurring simply by chance is determined. This is why there is no associated test statistic, just p.My question is: If the test is distributionless, wouldn't the probability of all unique results be equal? Or...put another way...Is Fisher's exact one of those sneaky nonparametrics that really does rely upon an underlying distribution? Thanks. . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ E. Jacquelin Dietz (919) 515-1929 (phone) Department of Statistics, Box 8203 (919) 515-1169 (FAX) North Carolina State University Raleigh, NC 27695-8203 USA [EMAIL PROTECTED] Street address for FedEx: Room 210E Patterson Hall, 2501 Founders Drive ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
