Date: Fri, 2 Sep 2005 15:13:21 -0500
Reply-To: "Granaas, Michael" <mgranaas@usd.edu>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: "Granaas, Michael" <mgranaas@usd.edu>
Subject: Re: MANOVA vs. Repeated Measures ANOVA
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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
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-----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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