[R-meta] Calculating SMD from posttest only - is this possible?
Viechtbauer, Wolfgang (SP)
wo||g@ng@v|echtb@uer @end|ng |rom m@@@tr|chtun|ver@|ty@n|
Sat Oct 5 23:40:52 CEST 2019
Hi Roberto,
Yes. In fact, that's essentially the original definition of the SMD, that is, the difference between two groups at the posttest divided by the SD (at the posttest).
One can debate to what extent the standardized mean change (of a single group), the difference between two standardized mean changes (of two groups), and the standardized mean difference at the posttest (again, of two groups) can be combined in a single analysis. The canonical reference regarding this issue is:
Morris, S. B., & DeShon, R. P. (2002). Combining effect size estimates in meta-analysis with repeated measures and independent-groups designs. Psychological Methods, 7(1), 105-125.
Best,
Wolfgang
-----Original Message-----
From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org] On Behalf Of P. Roberto Bakker
Sent: Thursday, 03 October, 2019 18:54
To: r-sig-meta-analysis using r-project.org
Subject: [R-meta] Calculating SMD from posttest only - is this possible?
Hi everybody
I am performing a meta-analysis (with 'metafor' R-project) as described by
Becker (1988), and I compute the standardized mean change for a treatment
and control group.
I compute a (standardized) effect size measure for pretest posttest control
group designs, where the characteristic, response, or dependent variable
assessed in the individual studies is a quantitative variable (Morris 2008).
Now, two new articles are published recently with only the posttests.
Question: can SMDs still be calculated with only the posttest (and sd) of
treatment and control groups?
Thank you in advance, Roberto
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