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
@BOOK{sutton00,
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:i...@aghmed.fsnet.co.uk>Michael Dewey
Date: 2013-04-27 07:28
To: <mailto:qiangm...@gmail.com>qiangmoon; <mailto:w...@wvbauer.com>wvb
CC: <mailto:r-help@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¡ÃSD of percentage change,
>i.e., the Mean¡ÃSD of (value of ¡®after¡¯-value
>of ¡®before¡¯)/value of
>¡®before¡¯¡Ã100%£¬without reporting the Mean¡ÃSD
>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
i...@aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html
Michael Dewey
i...@aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html
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