Date:         Fri, 12 Aug 2005 13:07:11 -0500
Reply-To:     "Swank, Paul R" <Paul.R.Swank@uth.tmc.edu>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         "Swank, Paul R" <Paul.R.Swank@uth.tmc.edu>
Subject:      Re: effect size form F and df
Comments: To: Matthew Pirritano <mpirrita@unm.edu>
Content-Type: text/plain; charset="us-ascii"

d = the difference in means divided by the standard deviation. Assuming
a two group design, F is the difference between means squared over the
pooled variance multiplied by [1/n(1) + 1/n(2)] so that

effect size squared is F times [1/n(1) + 1/n(2)]. If the n's are equal
then this becomes F*(2/n) so that the effect size is the square root of
[F*(2/n)].


Paul R. Swank, Ph.D.
Professor, Developmental Pediatrics
Medical School
UT Health Science Center at Houston

-----Original Message-----
From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of
Matthew Pirritano
Sent: Friday, August 12, 2005 9:51 AM
To: SPSSX-L@LISTSERV.UGA.EDU
Subject: effect size form F and df

Hello all,


I want to calculate cohen's d from and F and df.  Does anyone know how
to do this, or if it is possible?

I was thinking that I could just use this equation, since F is just t
squared.  I could take the square root of the F and then run this
syntax.  Does that make sense?


**

*SPSS*:

COMPUTE est_dbyt = (2 * t_value) / sqrt(df) .

EXECUTE .


Thanks
Matt

Matthew Pirritano, Ph.D.
National Science Foundation Post-Doctoral Fellow College of Education
Department of Individual, Family & Community Education
MSC05 3040
1 University of New Mexico
Albuquerque, NM 87131-0001
Telephone (505)277-7115
FAX (505)277-8361