On Tue, 19 Feb 2002, Wuensch, Karl L wrote: > > I would not put too much effort into making sense of this, since it is > highly unlikely that Fisher's exact test is appropriate for your data. > Fisher's exact test is only appropriate when both of your pairs of marginals > are fixed -- that is, when you could specify, prior to obtaining the data, > exactly what both pairs of marginal frequencies would be <snip> > > A traditional Pearson chi-square, NOT corrected for continuity, would be > appropriate.
I appreciate Karl's expertise in helping me make sense of this apparently anomalous result. But I wonder whether his interpretation of the Fisher is unduly conservative. My copy of an old edition (the first, actually!) of Siegel's classic _Non-Parametric Statistics for the Behavioral Sciences_ says this about the requirements for use of the Fisher: "The Fisher exact probability test is an extremely useful noparametric technique for analyzing discrete data (either nominal or ordinal) when the two independent samples are small in size. It is used when the scores from two independent random samples all fall into one or the other of two mutually exclusive classes. In other words, every subject in both groups obtains one of two possible scores". Of course, the chi-square is a more common alternative. But for some other proportions in the same data set, small cell size made chi-square use invalid. So for consistency, I thought it best to use the Fisher for all the tests. The problem seems to be with that left tail! -Stephen ------------------------------------------------------------------------ Stephen Black, Ph.D. tel: (819) 822-9600 ext 2470 Department of Psychology fax: (819) 822-9661 Bishop's University e-mail: [EMAIL PROTECTED] Lennoxville, QC J1M 1Z7 Canada Department web page at http://www.ubishops.ca/ccc/div/soc/psy Check out TIPS listserv for teachers of psychology at: http://www.frostburg.edu/dept/psyc/southerly/tips/ ------------------------------------------------------------------------ --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]
