Hi
Is there any way to fit a bivaraite longitudinal mixed model using R. I have
a data set with col names

resp1 (Y_ij1),  resp2 (Y_ij2),  timepts (t_ij),  unit(i)

 j=1,2,..,m  and  i=1,2,..n.

I want to fit the following two models

Model 1

Y_ij1, Y_ij2 | U_i = u_i ~ N(alpha + u_i + beta1*t_ij, Sigma)
U_i ~ iid N(0, sigu^2)

Sigma = bivariate AR structure

alpha and beta are vectors of order 2.

Model 2
Y_ij, Y_ij2  | U_i = u_i ~ N(alpha + u_i + beta1*t_ij + U_i2*t_ij, Sigma)

U_i=(U_i1,U_i2) ~ iid N(0, Omega)

Sigma =bivariate AR structure

Here alpha and beta are vectors of order 2.

Moreover can we assume a structure for Omega.

Any help is greatly appreciated.
 Souvik Banerjee
Junior Research Fellow
Dept of Statistics
University of calcutta

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