[R] questions about "metafor" package

[Michael Dewey]

At 16:21 17/08/2011, Emilie MAILLARD wrote:
>Hello,
>Â
>I would like to do a meta-analysis with the 
>package « metafor ». Ideally I would like to 
>use a mixed model because I’m interested to 
>see the effect of some moderators. But the data 
>set I managed to collect from literature presents two limits.
>Â
>-Â Â Â Â Â Â Â Â  Firstly, for each observation, 
>I have means for a treatment and for a control, 
>but I don’t always have corresponding standard 
>deviations (52 of a total of 93 observations 
>don’t have standard deviations). Nevertheless 
>I have the sample sizes for all observations so 
>I wonder if it was possible to weight 
>observations by sample size in the package « metafor ».
>-Â Â Â Â Â Â Â Â  Secondly, some observations 
>are probably not independent as I have sometimes 
>several relevant observations for a same design. 
>More precisely, for these cases, the control 
>mean is identical but treatment means varied. 
>Ideally, I would not like to do a weighted 
>average for these non-independent observations 
>because these observations represent levels of a 
>moderator. I know that the package « metafor 
>» is not designed for the analysis of 
>correlated outcomes. What are the dangers of 
>using the package even if observations are not really independent ? Â

Emilie,
I am not sure whether this is the answer to your 
problem of observations which are not independent 
but you might also look at the metaSEM package
http://courses.nus.edu.sg/course/psycwlm/internet/metaSEM/
I am still trying to understand his paper on this 
(see link for reference) but he is trying to 
embed meta-analysis within the structural 
equation framework and it may be possible to cope 
with lack of independence in that way. But as I 
say I am still trying to come to grips with the paper.


>Â
>Thank you for your help,
>Â
>Émilie.
>         [[alternative HTML version deleted]]

Michael Dewey
info at aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html