```Date: Mon, 26 May 2003 07:03:57 -0500 Reply-To: Anthony Babinec Sender: "SPSSX(r) Discussion" From: Anthony Babinec Subject: Re: SPSS 10.x Win DFA interpretation still need HELP!!!! Comments: To: WCS-Belize In-Reply-To: <5.1.1.6.2.20030526053137.00bd6008@pop.starband.net> Content-Type: text/plain; charset="iso-8859-1" P(g|d) is the posterior probability of being in group g given the discriminant score. For 3 groups, the 3 probs will sum to 1. The case is assigned to the group with the highest prob. These are the probabilities you want. The output shows highest group assignment and probability, and then the second highest group assignment and probability. For a 3 group problem, the third group probability is 1 minus the sum of the first two group probabilities. P(d|g) is the likelihood. It is computed under the assumption of within-groups normality plus some assumptions about the structure of the covariance matrices. P(g) is the prior. Bayes theorem is used to obtain p(g|d) from knowledge of the other two probs. Anthony Babinec -----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of WCS-Belize Sent: Monday, May 26, 2003 6:39 AM To: SPSSX-L@LISTSERV.UGA.EDU Subject: SPSS 10.x Win DFA interpretation still need HELP!!!! Importance: High Hi all, Running SPSS 10.x Windows. Running DFA and have a question on the probabilities given in the Case Wise Statistics table. Being way out in the jungle we have limited resources (no discussion with colleagues) so all of you out there are the support network :-) The SPPS results Coach provides an explanation that is 180° from what was given in a few examples provided on WWW sites using DFA. This is confusing at best. So can someone like Arthur J. Kendall help with the explanation of interpretation of the various probabilities displayed in SPSS when you run DFA? The first display is P(D>d| G=g) over p and df, the followed by P(G=g|D=d) and then the second group P(G=g|D=d) is given. What is not clear, at least for a dumb field biologist :-) is which of the probabilities are used to determine which is the predicted group membership. What is important is to determine when unclassified cases are classified incorrectly into a class they do not belong to. This is for cases when they actually do not belong to a predefined or classified case at all. Thanks again for all the previous replies that were close but did not answer the key question. Cheers from the Jungles of Belize. Bruce W. Miller Associate Conservation Zoologist Wildlife Conservation Society (founded in 1895 as the New York Zoological Society) Gallon Jug, Belize Mailing address P.O. Box 37, Belize City Belize, Central America NEW Phone/Fax +501-220-9002 Visit the Belize Biodiversity Information System or the Neotropical Bat Information System at http://fwie.fw.vt.edu/wcs/ OR Check out the WCS web site at: http://www.wcs.org OR Check out information on the Jaguar Conservation Program at http://www.savethejaguar.com ```

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