Dear all,

I'm currently applying a mixed model approach to meta analysis using the
package metafor. I use the "model.matrix()" function to create dummy
variables. The option btt gives me the combined test for the dummies.
Problem is, I don't know which indices I have to use, and can't really
figure it out from the help file and the examples. I use following code :

X <- model.matrix(~factor, data=testdata)[,2:5] # to exclude the intercept.
Otherwise I get singular issues in the rma model

rma(ai, bi, ci, di, mods=X, data=testdata,btt=c(2:5),measure="OR")

Now I'm not sure whether btt reads the model intercept of rma as index 1, or
the first dummy as index 1. So I'm not sure if I should use :

rma(ai, bi, ci, di, mods=X, data=testdata,btt=c(1:4),measure="OR")

from the examples in the help files, I should use the first option. But
there I see no option used to exclude an intercept from the model matrix.
All help greatly appreciated. Thank you in advance
Joris


-- 
Joris FA Meys
Statistical Consultant

Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control

Coupure Links 653
B-9000 Gent

tel : 09/ 264 59 87
Joris.Meys@Ugent.be
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