[R] metafor package: study level variation

[Michael Dewey]

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