[R-sig-ME] Random intercept/slopes on two correlated outcomes

[Theodore Lytras]

Hi all,

I have repeated measures on individuals, and I'm fitting two LMMs with random 
intercepts and slopes per participant, on two outcomes (Y1, Y2) as follows:

library(lme4)
m1 <- lmer(Y1 ~ age + X + (age | id), data=dat)
m2 <- lmer(Y2 ~ age + X + (age | id), data=dat)

Fixed covariates for the two outcomes are the same, and id = participant ID.

However, my two continuous outcomes Y1 and Y2 are correlated (highly), thus I 
would like to jointly model them (including estimating their correlation).

What is the appropriate way to do so in this case? Can lme4 do it, or do I 
have to resort to MCMCglmm or JAGS? Could someone point me in the right 
direction (for either lme4, MCMCglmm or JAGS), including any helpful papers, 
guides, etc ??

Thank you,

Theodore Lytras

Epidemiologist, PhD student
Hellenic Centre for Disease Control and Prevention