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
i...@aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html
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