[R-meta] Meta-analysis Hedges g - comparisons with same placebo

[Viechtbauer Wolfgang (SP)]

There is also code for computing the covariance among the standardized mean differences in such 'multitreatment' studies here:

http://www.metafor-project.org/doku.php/analyses:gleser2009

Best,
Wolfgang

-----Original Message-----
From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-project.org] On Behalf Of Gerta Ruecker
Sent: Wednesday, 18 October, 2017 13:28
To: P. Roberto Bakker
Cc: r-sig-meta-analysis at r-project.org
Subject: Re: [R-meta] Meta-analysis Hedges g - comparisons with same placebo

As I wrote in my response, see our paper 
http://onlinelibrary.wiley.com/doi/10.1002/jrsm.1259/full 
<http://onlinelibrary.wiley.com/doi/10.1002/jrsm.1259/full> .

Best,

Gerta

Am 18.10.2017 um 13:10 schrieb P. Roberto Bakker:
> 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 Rücker, 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