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

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 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