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Date:         Fri, 9 Jun 2000 08:50:48 -0700
Reply-To:     glaser@pacific-science.com
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Dale Glaser <glaser@PACIFIC-SCIENCE.COM>
Subject:      Re: eta squared in UNIVARIATE GLM
Comments: To: "Perkins, Nigel" <N.R.Perkins@MASSEY.AC.NZ>
In-Reply-To:  <E57866E2EBE3D311B3720008C78409312318B9@its-xchg2.massey.ac.nz>
Content-Type: text/plain; charset="iso-8859-1"

If I recall, technically it is a partial eta-squared, as opposed to eta squared; if you use the MANOVA option (via syntax only), it provides both eta squaredand partial eta squared, whereas with the GLM option only the partial is reported even though it is mistakenly labeled as eta squared (Dave Nichols please correct me if I'm off base here)..........dale glaser

-----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Perkins, Nigel Sent: Thursday, June 08, 2000 9:01 PM To: SPSSX-L@LISTSERV.UGA.EDU Subject: eta squared in UNIVARIATE GLM

I am trying to come to grips with the eta squared term in the UNIVARIATE GLM procedure of SPSS (using version 9.0). I am using one way and 2-way factorial ANOVAs to produce power and effect size estimates.

Several textbooks mention a term labelled eta squared or R-squared which appears to be interpreted in the same way as the eta squared value in SPSS (percent variance explained). Textbooks such as Cohen (Statistical power analysis for the behavioral sciences) and Kirk (Experimental design) mention that eta squared should be related to effect size in the following manner:

f-squared = eta squared / (1- eta squared)

However, when I attempt to use a text book derived formula for estimating eta squared and then compare it to the SPSS value, they are not the same! This occurs even in a 1-way ANOVA (using a simple example) when degrees of freedom estimation is straight forward and not term dependent.

Can anyone explain why the SPSS eta-squared term does not appear to be related to the effect size term in the way that Cohen and Kirk and others say that it should be? Regards, Nigel Perkins, BVSc, MS, Dip ACT, FACVSc Senior Lecturer, Veterinary Epidemiology EpiCentre, IVABS Massey University Private Bag 11222 Palmerston North New Zealand N.R.Perkins@massey.ac.nz http://epicentre.massey.ac.nz


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