[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|
Mon Oct 7 22:13:32 CEST 2019
That is correct when using standardized mean change values using change score standardization -- and indeed, that's not something that should done. However, the standardized mean change using raw score standardization also standardizes based on the variability at a single time point and hence is in principle comparable to the standardized mean difference at the posttest (leaving aside other issues, such as time effects). I would still be very careful when doing this and I very much like Michael's suggestion to examine this via a moderator analysis.
From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org] On Behalf Of Guido Schwarzer
Sent: Monday, 07 October, 2019 14:16
To: P. Roberto Bakker; r-sig-meta-analysis using r-project.org
Subject: Re: [R-meta] Calculating SMD from posttest only - is this possible?
Just to add to the responses by Wolfgang and James.
The Cochrane Handbook warns against combining SMDs based on change
scores (pre-post comparisons) and post-test comparisons (see
The reason is that the standard deviation used in the denominator of the
SMD is different for change scores and post-tests.
Best wishes, Guido
Dr. Guido Schwarzer
Institute of Medical Biometry and Statistics,
Faculty of Medicine and Medical Center - University of Freiburg
Postal address: Stefan-Meier-Str. 26, D-79104 Freiburg
Mail: sc using imbi.uni-freiburg.de
ORCID iD: https://orcid.org/0000-0001-6214-9087
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