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

[Viechtbauer, Wolfgang (SP)]

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.

Best,
Wolfgang

-----Original Message-----
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?

Hi Roberto,

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 
https://training.cochrane.org/handbook/current/chapter-10#section-10-5-2). 
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

Phone: +49/761/203-6668
Mail: sc using imbi.uni-freiburg.de
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