[R] using metafor for meta-analysis of before-after studies

Michael Dewey info at aghmed.fsnet.co.uk
Sun Apr 28 12:30:41 CEST 2013

At 16:50 27/04/2013, Qiang Yue wrote:
>Hello, Michael.
>Thanks for your kind and rapid reply, and sorry 
>for the inconvenience of characters.
>Yes,  the primary studies reported the n, the 
>mean percentage change and its standard 
>deviation, but some did not report the original 
>value of before- or after-intervention, and 
>there is only one group because these are 
>uncontrolled  before-and-after studies.

If you have a series of non-comparative studies 
then you can proceed. Of course all you are 
estimating is subject to the usual caveats about 
uncontrolled before and after studies. Look in 
the escalc documentation under the heading 
Outcome measures for individual groups.

>  So you mean we can not perform meta-analysis 
> based on the mean percentage change and its standard deviation?

That is not what I said, or what I intended to 
say although my message may not have been 
directly relevant as I did not grasp the sort of study you were dealing with.

>For studies which have reported the original 
>value  of before- and after-intervention, can I 
>just simply treat the before-intervention values 
>as the values of control group and treat the 
>after-intervention values as the values of intervention group?

That would seem a strange thing to want to do.

>  I will be grateful if you can send me some of 
> your publications of meta-analysis on 
> before-after study, thus I can learn how to perform the analysis.

I think you need to get some local help on the 
ideas behind meta-analysis or read a good book

   author = {Sutton, A J and Abrams, K R and Jones, D R and Sheldon, T A and
            Song, F},
   year = 2000,
   title = {Methods for meta-analysis in medical research},
   publisher = {Wiley},
   address = {Chichester},
   keywords = {meta-analysis, general}

might be a good choice given your affiliation.

>With best regards.
>Qiang Yue
>From: <mailto:info at aghmed.fsnet.co.uk>Michael Dewey
>Date: 2013-04-27 07:28
>To: <mailto:qiangmoon at gmail.com>qiangmoon; <mailto:wvb at wvbauer.com>wvb
>CC: <mailto:r-help at r-project.org>r-help
>Subject: Re: [R] using metafor for meta-analysis of before-after studies
>At 03:27 27/04/2013, Qiang Yue wrote:
> >Hello, Dr. Viechtbauer.
> >
> >I am trying to perform a meta-analyis on a group
> >of before-after studies using Metafor. I read
> >your webpage including your correspondence with
> >Dr. Dewey
> >(https://stat.ethz.ch/pipermail/r-help/2012-April/308946.html),
> >who also conducted a similar study. These
> >information is very hepful, but I have one
> >additonal question which I wonder if you can
> >give me some instruction. The question is as follow:
> >
> >These studies which we are trying to analyze are
> >performed on the same subject before and after
> >the adminstration of intervention. Most studies
> >reported the the Mean¡ÀSD of percentage change,
> >i.e., the Mean¡ÀSD of (value of ¡®after¡¯-value
> >of ¡®before¡¯)/value of
> >¡®before¡¯¡Á100%£¬without reporting the Mean¡ÀSD
> >of value of ¡®after¡¯ or value of ¡®before¡¯. So
> >I want to know if it is possible to perform
> >meta-analyis using the value of percentage
> >change, and if it is possible to calculate the
> >¡®sdi¡¯ (the standard deviation of the change
> >scores) using the SD of percentage change.
>Unfortunately not all the characters in your
>email appeared correctly here but if I understand
>you correctly the primary studies have reported
>(for each group?) mean percentage change and its
>standard deviation (and presumably the n). So you
>just treat them like any other mean and standard deviation.
>If I understand the very last part correctly you
>would need more information than we have to back
>calculate change on the original scale from change on the percentage scale.
> >
> >Thank you very much, I am looking forward to your reply.
> >
> >With best wishes.
> >
> >
> >
> >
> >Qiang Yue M.D.
> >Visiting Scholar of IMHR, University of Ottawa
> >1145 Carling Avenue, K1Z 7K4, Ottawa, ON, Canada
> >Tel: 613-722-6521 ext. 6554
> >Associate Professor of Radiology
> >Department of Radiology, West China Hospital, Sichuan University
> >Chengdu, 610041, China  [[alternative HTML version deleted]]
>Michael Dewey
>info at aghmed.fsnet.co.uk

Michael Dewey
info at aghmed.fsnet.co.uk

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