At 15:02 07/09/2012, Jarrett Byrnes wrote:
Hello. A quick question about incorporating variation due to study
in the metafor package. I'm working with a particular data set for
meta-analysis where some studies have multiple measurements. Others
do not. So, let's say the effect I'm looking at is response to two
different kinds of drug treatment - let's call their effect sizes T1
and T2. Some studies have multiple experiments measuring T1 and
T2. Some have one of each. Some only have T1 or T2.
I think that you have the situation which is usually dealt with by
some sort of network meta-analysis and as far as I know, although I
am sure I shall quickly be told if I am wrong, you have to organise
this yourself.
If you ignore the studies which only give rise to one effect size you
could explore whether mvmeta works for your dataset although you may
need to have information (on the variance-covariance matrix( which I
suspect you do not have.
Now, in metafor, I've been using
rma(yi = logRatio, vi=varLogRatio, mods=~ Drug.Type, data=mydata)
This works fine. Out of curiosity, I ran a quickie model in lme4
lmer(logRatio ~ Drug.Type + (1+studyID), data=mydata, weights=varLogRatio)
and I noticed that the results are quite different, and this appears
due to some variation due to study (after inspecting ranef - note, I
included Drug.Type as a fixed effect as there were only two levels).
So, I went back to metafor and ran
rma(yi = logRatio, vi=varLogRatio, mods=~ Drug.Type+studyID, data=mydata)
which yielded the error
Error in qr.solve(wX, diag(k)) : singular matrix 'a' in solve
In addition: Warning message:
In rma(yi = logRatio, vi = varLogRatio, data = mydata, mods = ~Drug.Type :
Cases with NAs omitted from model fitting.
which appears to be due to the unbalanced nature of the dataset
(some studies having T1 and T2, some having multiple measures of T1 and T2).
So, is there a way to properly incorporate studyID in a metafor
using rma? Is there an argument I'm missing, or perhaps should be
using a different function?
Thanks!
-Jarrett
Michael Dewey
i...@aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html
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