If you take the sample sizes into account, you won't have an effect size
since they are independent of sample size. You can take the variances
into account, depending on the type of effect size you want to use. In
this case you could use Cohen's d or a variant like Glass' coefficient.
Or you could use Cohen's f or f-squared statistic. Any of these would
use the pooled variances weighted by df. See
Cohen, J. (1988). Statistical Power Analysis for the Behavioral Sciences
(2nd ed.). Hillside, NJ:Erlbaum.
Paul R. Swank, Ph.D
Professor and Director of Research
Children's Learning Institute
University of Texas Health Science Center
Houston, TX 77038
-----Original Message-----
From: SPSSX(r) Discussion [mailto:
[hidden email]] On Behalf Of
AD
Sent: Thursday, January 29, 2009 2:56 PM
To:
[hidden email]
Subject: Unequal variances and effect size
I am comparing the means of four groups with extremely unequal sample
sizes. I would like to obtain an effect size for my analysis that will
take
into account sample size differences or variance differences. Is there
any
wy I can do that?
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