Is there a way to specify two different random intercept terms for two sub-groups of subjects within a single mixed model? The reason why I'm interested is that it seems that the inter-personal variability of one group of subjects on my task is greater than the inter-personal variability of the other. I'm using lmer and currently specifying the subject factor as a random intercept, which pools all my participants into a single estimate, but I would like to have two separate estimates for the two sub-groups.
Using the "weights" argument in R's nlme you can allow for separate variances for each level of a grouping variable (heterogeneous variability).
For examples see: