Hi Gerta,
Thank you for your reply and suggestions.
Our meta-analysis is not a network meta-analysis but a 'regular', i.e.
pairwise. Do you have suggestion how to adjust for this?
Bw,
Roberto
Op 18 okt. 2017 10:41 a.m. schreef "Gerta Ruecker"
<ruecker at imbi.uni-freiburg.de <mailto:ruecker at imbi.uni-freiburg.de>>:
Dear Roberto,
it is a network meta-analysis what you are planning? Do you think of
multi-arm studies including a placebo group? If so, and if it is the
same placebo that is compared to several antidepressants, then I think
there is no problem. The different placebo groups in different studies
provide independent information and network meta-analysis may in fact
increase precision (provided you have loops in your network), but this
is exactly what network meta-analysis is intended to do.
To avoid misunderstandings: What you should not do is to use a placebo
group in a multi-arm study twice in a pairwise meta-analysis without
adjustment.
For an introduction, see
http://onlinelibrary.wiley.com/doi/10.1002/jrsm.1259/full
<http://onlinelibrary.wiley.com/doi/10.1002/jrsm.1259/full> .
Best,
Gerta
--
Dr. rer. nat. Gerta R?cker, Dipl.-Math.
Medical Faculty and Medical Center - University of Freiburg
Institute for Medical Biometry and Statistics
Stefan-Meier-Strasse 26, D-79104 Freiburg, Germany
Phone +49 (0)761 2036673 <tel:%2B49%20%280%29761%202036673>
Fax +49 (0)761 2036680 <tel:%2B49%20%280%29761%202036680>
Mailruecker at imbi.uni-freiburg.de
<mailto:Mailruecker at imbi.uni-freiburg.de>
Webwww.imbi.uni-freiburg.de/biom/
<http://Webwww.imbi.uni-freiburg.de/biom/>
Am 18.10.2017 um 08:12 schrieb P. Roberto Bakker:
> Hi,
>
> We are conducting a meta-analysis of RCTs between
antidepressants and placebo and calculate Hedges g.
> Question:
> How can we deal with studies which compare different
antidepressants with the same placebo? Our concern is when we
include the different antidepressant comparisons with the same
placebo in the meta-analysis the placebo size will increase
artificially which will lead to more precise spurious results. If
our reasoning is correct, how can we deal this?
>
> Thank you in advance,
>
> Roberto
>
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