[R-sig-ME] confidence intervals of VPC

[Julien Martin]

Hi
when using a model mixed with both a random intercept and slope such as 
lmer( y ~ x + ( x | group) )
we could computed the variance partition coefficient (VPC) as suggested 
by Goldstein et al 2002.
VPC_x = (Vi + X*cov(I,S) + X^2 * Vs) / (Vi + X * cov(I,S) + X^2 * Vs + Vr)
I am wondering how we could obtain confidence intervals for VPC using lmer.
Thanks
Julien