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Date:         Wed, 19 Jul 2006 10:13:55 -0700
Reply-To:     Dale Glaser <glaserconsult@sbcglobal.net>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Dale Glaser <glaserconsult@sbcglobal.net>
Subject:      Re: effect size: eta-squared vs partial eta-squared
Comments: To: "Dogan, Enis" <edogan@air.org>
In-Reply-To:  <957C8A78DD5B6D42B7D33DBAB78CDC2F9ADCFB@dc2ex01.air.org>
Content-Type: text/plain; charset=iso-8859-1

Enis, in Keppel and Wickens (2004) the authors make a rather compelling argument against the R^2 effect size as reported in SPSS (i.e, SSa/SStotal) as opposed to omega squared, using their notation on page 164: (SSa - (a -1)MS s/a)/(SStotal + MS s/a)..they comment that omega squared "takes the sampling variability into account and so is most relevant to the population you are studying" (p. 167) and that, in their opinion, r^2 (which statistically can be shown) tends to inflate the variation accounted for.....however, SPSS does not report omega squared so one would need to hand calculate this estimate

Keppel, G., & Wickens, T. D. (2004). Design and analysis. (4th Ed.). Upper Saddle River, NJ: Pearson.

"Dogan, Enis" <edogan@air.org> wrote: Thanks to all who replied to my question. Any comments on the relationship between partial-eta squared and partial R squared? Also eta-squared looks to me like a part R squared. Any thoughts?

Enis

-----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Nicholas J.S. Gibson Sent: Wednesday, July 19, 2006 12:37 PM To: SPSSX-L@LISTSERV.UGA.EDU Subject: Re: effect size: eta-squared vs partial eta-squared

A quick search on "eta" in the archives will confirm that some variant of this question comes up pretty frequently! Unfortunately SPSS still has no capability to report total eta-squared values or the SS values needed to

calculate total eta-squared values for mixed-model ANOVAs by hand (unless this functionality has since been added to SPSS 14/15). When Kyle Weeks last commented on this (Jan 2003 -- see http://www.listserv.uga.edu/cgi-bin/wa?A2=ind0301&L=spssx-l&P=R2708&m=24 876 ) he said this feature was on the "wish list" but I don't know if it has

since become a reality. If someone knows of development or planned development on this it would be useful to know about it.

Reporting partial eta-squared values would indeed be misleading given that when summed they can exceed 1. Unfortunately without SPSS reporting total eta-squared values it is likely that researchers do erroneously report partial values.

Other articles on this include:

Timothy R. Levine & Craig R. Hullett. (2002). Eta squared, partial eta

squared, and misreporting of effect size in communication research. Human Communication Research, 28, 612-625.

Pierce, C. A., Block, R. A., & Aguinis, H. (2004). Cautionary note on reporting eta-squared values from multifactor ANOVA designs. Educational

and Psychological Measurement, 64, 916-924. http://www.montana.edu/wwwpy/Block/papers/Pierce,Block,&Aguinas-2004.pdf

Nicholas Gibson

-- Nicholas J.S. Gibson, Ph.D. Psychology and Religion Research Group Faculty of Divinity, University of Cambridge West Road, Cambridge, CB3 9BS, UK

tel +44 (0)1223 763010 * mob +44 (0)7970 757524 * fax +44 (0)1223 763003 http://www.divinity.cam.ac.uk/pcp/personnel/nicholas.html

> Date: Tue, 18 Jul 2006 12:01:26 -0500 > From: "Alexander J. Shackman" > > see also > > http://web.uccs.edu/lbecker/Psy590/es.htm > and > http://web.uccs.edu/lbecker/SPSS/glm_effectsize.htm > > On 7/18/06, Dogan, Enis wrote: > > > > Dear all > > > > > > > > SPSS reports partial et-sq as opposed to eta-squared. > > > > I found in the literature the rule thumb for eta-squared as small > > (0.01), medium (0.06), and large (0.14) (Cohen, 1988). > > > > Does this apply to partial eta-squared as well? > > > > Also, the definition of eta-squared gives me the idea that it is no > > different than what some of us call partial R squared. > > > > Am I right? > > > > > > > > There is rumor out there that "researchers erroneously report partial > > eta-squared values as representing classical eta-squared values" > > > > http://carbon.cudenver.edu/~haguinis/APMinpress.pdf > > > > > > > > Any value in this argument? > > > > > > > > Thanx > > > > > > > > Enis > > > > > > > >

Dale Glaser, Ph.D. Principal--Glaser Consulting Lecturer--SDSU/USD/CSUSM/AIU 4003 Goldfinch St, Suite G San Diego, CA 92103 phone: 619-220-0602 fax: 619-220-0412 email: glaserconsult@sbcglobal.net


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