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Date:         Wed, 28 Jan 2009 08:25:39 -0800
Reply-To:     SR Millis <srmillis@yahoo.com>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         SR Millis <srmillis@yahoo.com>
Subject:      Re: Discriminant Analysis - Testing Equal Covariances
In-Reply-To:  <6250203B042D8349A920AA610383093609B3CB77@UTHEVS3.mail.uthouston.edu>
Content-Type: text/plain; charset=us-ascii

To build on Paul's comment, DFA seems to be relatively robust to violations of the homogeneity assumption if the ratio of the larger group n divided by the smaller group n is less than 1.5 (Stevens, 1996). In SPSS you can test the assumption using Box's M.

Scott R Millis, PhD, MEd, ABPP (CN,CL,RP), CStat Professor & Director of Research Dept of Physical Medicine & Rehabilitation Wayne State University School of Medicine 261 Mack Blvd Detroit, MI 48201 Email: smillis@med.wayne.edu Tel: 313-993-8085 Fax: 313-966-7682

--- On Wed, 1/28/09, Swank, Paul R <Paul.R.Swank@uth.tmc.edu> wrote:

> From: Swank, Paul R <Paul.R.Swank@uth.tmc.edu> > Subject: Re: Discriminant Analysis - Testing Equal Covariances > To: SPSSX-L@LISTSERV.UGA.EDU > Date: Wednesday, January 28, 2009, 10:08 AM > I agree with Scott that logistic regression is probably best > here but if > you still wish to continue with the discriminant analysis, > recognize > that it is basically a MANOVA. So you can use the MANOVA > program to > compare the variance -covariance matrices, or at least I > assume so. > > Paul R. Swank, Ph.D > Professor and Director of Research > Children's Learning Institute > University of Texas Health Science Center > Houston, TX 77038 > > > -----Original Message----- > From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] > On Behalf Of > Peter Erhardt > Sent: Wednesday, January 28, 2009 7:54 AM > To: SPSSX-L@LISTSERV.UGA.EDU > Subject: Discriminant Analysis - Testing Equal Covariances > > I am doing discriminant analysis for 2 groups and I > don't see an option > to test whether the covariances between groups are equal. > In other > words, I don't know if I should be using the linear or > the quadratic > discriminant functions. In SPSS this is the "Use > Covariance Matrix: > "Within Groups" or "Separate Groups" > option. However, there is not a > third option to test this equality like there is in SAS. > > > > Anyone know of a way to do this in SPSS? Either with an > option under > discriminant analysis, or a separate test would be fine. > > > > I get digest mode usually, so I'd appreciate if you > respond to me > directly as well as the list. > > > > Thanks, > > Pete > > > > Peter Erhardt > > Data & Research Specialist > > Development & Alumni Relations > > Rochester Institute of Technology > > 116 Lomb Memorial Drive > > Rochester, NY 14623 > > 585-475-5039 || 585-475-7004 (F) > > ptedar@rit.edu > > > > ==========To manage your subscription to SPSSX-L, send a > message to > LISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no body > text except the > command. To leave the list, send the command > SIGNOFF SPSSX-L > For a list of commands to manage subscriptions, send the > command > INFO REFCARD > > ===================== > To manage your subscription to SPSSX-L, send a message to > LISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no body > text except the > command. To leave the list, send the command > SIGNOFF SPSSX-L > For a list of commands to manage subscriptions, send the > command > INFO REFCARD

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