[R] metafor matrix error

[Viechtbauer Wolfgang (STAT)]

Dear Branwen,

This means that your design matrix is not of full rank (in a more recent version of the metafor package, the error message is a bit more informative; i.e., please upgrade). Since "continent" is a factor, this should imply that one of the levels never actually occurs, leading to a column of 0s in the design matrix, which then causes the problem with the matrix inversion.

Best,
Wolfgang

--   
Wolfgang Viechtbauer, Ph.D., Statistician   
Department of Psychiatry and Psychology   
School for Mental Health and Neuroscience   
Faculty of Health, Medicine, and Life Sciences   
Maastricht University, P.O. Box 616 (VIJV1)   
6200 MD Maastricht, The Netherlands   
+31 (43) 388-4170 | http://www.wvbauer.com   


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of Branwen Owen
> Sent: Tuesday, May 21, 2013 23:12
> To: r-help at r-project.org
> Subject: [R] metafor matrix error
> 
> hi
>      I've been using this code to set a reference level for uni and
> multivariate analysis
>           rmix$interviewmethodcode<-
> relevel(mix$interviewmethodcode,ref="SAQ")
>           summary(rma.1<-
> rma(yi,vi,mods=~interviewmethodcode,data=rmix,method="SJ",knha=F,weighted=
> F,intercept=T))
>     giving this output:
>           Model Results:
>                               estimate      se     zval    pval    ci.lb
> ci.ub
>           intrcpt                     0.1437  0.0176   8.1485  <.0001
> 0.1091  0.1783  ***
>           interviewmethodcodeACASI    0.0022  0.0412   0.0545  0.9566  -
> 0.0784  0.0829
>           interviewmethodcodeFTFI    -0.0926  0.0656  -1.4112  0.1582  -
> 0.2213  0.0360
> 
> However, when i use the same code with a different variable (below) I get
> the error message -  "Error in qr.solve(wX, diag(k)) : singular matrix 'a'
> in solve".
>          rmix$continent<-relevel(mix$continent,ref="North America")
>          summary(rma.1<-
> rma(yi,vi,mods=~continent,data=rmix,method="SJ",knha=F,weighted=F,intercep
> t=T))
> 
> Can anyone help to see where the problem is?
>     thanks
>     Branwen
> 
> --
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> matrix-error-tp4667653.html
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