LISTSERV at the University of Georgia
Menubar Imagemap
Home Browse Manage Request Manuals Register
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (September 2005)Back to main SPSSX-L pageJoin or leave SPSSX-L (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Thu, 29 Sep 2005 09:31:52 +0200
Reply-To:     Marta García-Granero
              <biostatistics@terra.es>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Marta García-Granero
              <biostatistics@terra.es>
Organization: Asesoría Bioestadística
Subject:      Re: Hedges Unbiased Effect Size Estimator
In-Reply-To:  <54CF82BF475EF74583773795A396AD0C06BF4214@nt207mxsep.corporate.hdwa.health.wa.gov.au>
Content-Type: text/plain; charset=ISO-8859-15

Hi Jonathon,

To my knowledge, this formula is for 2 independent samples. Right now I don't have Egger's book on meta-analysis at hand, but I'll check if that particular topic is covered.

I seem to remember that I read (somewhere...) that the formula could be used for Cohen's d obtained from paired data considering n1=n2=n, but I'm not really really sure, because somewhere else I read that the Hedges estimator is only for independent samples.

See: http://web.uccs.edu/lbecker/Psy590/es.htm

I haven't had time to read the following paper slowly, but I think you can find something interesting in it: http://www.ucm.es/info/Psi/docs/journal/v2_n1_1999/art32.pdf

(Although it's a Spanish journal, only the summary is in Spanish, the rest of the paper is in English).

LJ> My question relates to the calculation of the confidence intervals for LJ> Hedges Unbiased Effect Size Estimator. Can someone clarify if this LJ> formula pasted below is appropriate for a single group pre-test LJ> post-test design (that is, repeated measures). I ask because Hedges and LJ> Olkin (1985, somewhere between 80-90) use the example of an experimental LJ> and control group (that is, independent groups, not repeated measures). LJ> In addition is anyone is able to offer any references which deal with LJ> the issue, then that would also be appreciated. LJ> I have pasted a portion of syntax provided by Marta Garcia-Granero LJ> below: LJ> COMPUTE poolvar=((n1-1)&*(sd1&**2)+(n2-1)&*(sd2&**2))/(n-2) . LJ> COMPUTE cohen=(mean1-mean2)/SQRT(poolvar). LJ> COMPUTE hedges=cohen&*(1-(3/(4&*(n)-9))). LJ> COMPUTE se_hedge=SQRT((n/(n1&*n2))+((hedges&**2)/(2&*(n-3.94)))).

Regards, Marta García-Granero mailto:biostatistics@terra.es


Back to: Top of message | Previous page | Main SPSSX-L page