Dear userlist,

I recently updated the lme4 package to version 1.0-6 and have the
impression formulas are not interpreted exactly the same way as before.

I am trying to fit a mixed effect model with independent random effects for
the covariates, that is:

logit(y_ij) = b_0i + b_1i x1_ij + b_2i x2_ij
where
b_0i ~ N(beta0, tau0)
b_1i ~ N(beta1, tau1)
b_2i ~N(beta2, tau2)

i indicates the subject, j indicates an index of different study IDs.

In want to specify random slopes for b1 and b2, and a random intercept for
b0. The variables x0 and x1 are binary, and take values 0 or 1. I have
constructed the following formula:

"y~ x1 + x2+(1|studyid) + ( x1 -1|studyid)+( x2 -1|studyid)"


In one of the earlier versions of lme4, I would have gotten something like this:


Random effects:
 Groups    Name        Std.Dev.
 studyid   (Intercept) 2.217e-04
 studyid.1 x1        2.518e-05
 studyid.2 x2     8.891e-05


where tau0, tau1 and tau2 are indicated by the Std.Dev. Now, in the latest
version of lme4 I get:


Random effects:
 Groups    Name        Std.Dev.  Corr
 studyid   (Intercept) 2.217e-04
 studyid.1 x10        2.518e-05
           x11        4.480e-04 0.08
 studyid.2 x20     8.891e-05

           x21     1.108e-04 0.79



Can someone tell me whether I am doing something wrong, or how I
should adjust my formula to estimate the specified model?


Thanks in advance!


Thomas

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