Message-ID: <035b8ae7-6fc3-bbfe-1422-99298264551e@dewey.myzen.co.uk>
Date: 2019-10-07T12:57:33Z
From: Michael Dewey
Subject: [R-meta] Calculating SMD from posttest only - is this possible?
In-Reply-To: <25df3e2ee4e1432aa92a6b77a8e03922@UM-MAIL3214.unimaas.nl>
Dear Roberto
You may have already thought of this but including a categorical
moderator to distinguish the designs would be useful. Of course if it
shows that the designs give different results you have the problem of
explaining it but at least you know.
This is a supplement to the advice from W, J and G.
Michael
On 05/10/2019 22:40, Viechtbauer, Wolfgang (SP) wrote:
> 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 at r-project.org] On Behalf Of P. Roberto Bakker
> Sent: Thursday, 03 October, 2019 18:54
> To: r-sig-meta-analysis at 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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>
--
Michael
http://www.dewey.myzen.co.uk/home.html