[R-meta] Calculating SMD from posttest only - is this possible?
P. Roberto Bakker
robertob@kker @end|ng |rom gm@||@com
Tue Oct 8 03:46:51 CEST 2019
Hi Wolfgang, Guido, Michael, and James,
Your information and explanation are really helpful, interesting and
important. A lot of my questions now have a clear answer, and I
understand better what needs to be done. I will bring your information to
my meta-analysis group. As your information is published in the
R-sig-meta-analysis Archives, other people will benefit.
Thank you very much and best regards,
Op ma 7 okt. 2019 om 13:13 schreef Viechtbauer, Wolfgang (SP) <
wolfgang.viechtbauer using maastrichtuniversity.nl>:
> 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.
> -----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
> 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
> 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
> Homepage: http://www.imbi.uni-freiburg.de
> ORCID iD: https://orcid.org/0000-0001-6214-9087
> R-book: https://www.springer.com/gp/book/9783319214153
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