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>
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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
>
>
>
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