[R-meta] Calculating SMD from posttest only - is this possible?
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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