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Date:         Fri, 2 Sep 2005 16:50:01 -0400
Reply-To:     "Jin, Shihou" <sjin@udsmr.org>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         "Jin, Shihou" <sjin@udsmr.org>
Subject:      Re: MANOVA vs. Repeated Measures ANOVA
Comments: To: mgranaas@usd.edu
Content-Type: text/plain; charset="us-ascii"

One problem to analyze pre-post data with ANCOVA instead of ANOVA is that it might lead to collinearity problem if the change score is highly related the pretest score

"Granaas, Michael" <mgranaas@usd.edu> wrote in message news: <C13C4AD72F0C3142BF4AE9B874A4A0E705C51C@usd-ex01.usd.local>... There are a couple of reasons for this difference you observe:

First, ANCOVA is often used as a means of last resort to try and detect significance in a poorly designed study and so is sometimes avoided.

Second, the reality that ANCOVA can be used as an alternative to repeated measures in a pre-post is rarely taught in Psychology Depts. Not sure why, but the idea of "change score" is pretty firmly embedded and I'm guessing that it is hard for researcher's to get their head around the idea that the ANCOVA approach is legitimate and in many cases better.

Michael **************************************************** Michael Granaas mgranaas@usd.edu Assoc. Prof. Phone: 605 677 5295 Dept. of Psychology FAX: 605 677 3195 University of South Dakota 414 E. Clark St. Vermillion, SD 57069 *****************************************************

-----Original Message----- From: SPSSX(r) Discussion on behalf of MacLennan, Graeme Sent: Fri 9/2/05 5:52 AM To: SPSSX-L@LISTSERV.UGA.EDU Subject: Re: MANOVA vs. Repeated Measures ANOVA

Dear listers, as an aside to this thread, I would always choose ANCOVA over repeated measures ANOVA for pre to post intervention data(that is only two time points). As a medical statistician ANCOVA is a fairly bog standard tool, but as I work more with psychologists I see repeated measures ANOVA used in its stead for pre test post test scores set up, analogous to a randomised controlled trial in medicine. Is there a real divide on this issue or am I imagining it? We medical statos use ANCOVA because we are told to, see Vickers AJ, Altman DG. Bmj 2001: 323(7321); 1123-4, Senn S. Statistics in Medicine 2000: 19; 861-877, but I would like to see any arguments in the literature to the contrary.

I look forward to any views on this.

Kind regards, Graeme.

-----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Keith Starborn Sent: 01 September 2005 20:43 To: SPSSX-L@LISTSERV.UGA.EDU Subject: Re: MANOVA vs. Repeated Measures ANOVA

Keith Starborn www.statisticsdoc.com

Dear Lana,

Dr. Swanks' suggestion regarding Huberty and Morris (1989) is an excellent one (as is the reference to Tabachnick & Fidellas by Dr. Buchanan). Many journal editors, and an entire generation of graduate students in Education and behavioral sciences, have been socialized to believe that a significant MANOVA is a necessary condition for conducting ANOVAs, that MANOVAs are needed whenever a study has more than one dependent variable in order to guard against inflated alpha levels, and that the need for MANOVA is even greater when the dependent variables are correlated. These assumptions have been disputed most notably by Huberty and Morris (1989) and others.

Having said that, you may or may not glean some interesting insights from asking multivariate questions of your data, along the lines discussed by Huberty and Morris. Do you consider your set of five dependent variables to measure a complex of related school adjustment variables? Are the program activities ones that you would expect to impact on this set of school adjustment variables? Are you perhaps interested in the multivariate structure of the relationships between program actitivities and change in multiple school adjustment indices?

HTH,

KS

Quoting "Yampolskaya, Svetlana" <yampol@fmhi.usf.edu>:

> Dear List, > > I have 5 DV (i.e., student GPA, number of disciplinary referrals, days a > student was absent from school, etc.). These DVs were measures twice > (the beginning of the semester and at the end). My IV is level of > participation in program activiteis. I used Repeated Measures ANOVA. > The reviewers of the manuscript made the following comment: > > Why MANOVAs (vs ANOVA) were not conducted to account for the > correlations (relatedness) between dependent variables? > > Can anybody help and explain when it is more appropriate to use MANOVA > vs ANOVA? > > Thank you in advance, > > Lana >

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