Well I may be ignorant also, but as far as I can tell lme4/lmer doesnt have ANY options to specify the variance-covariance matrix while SPSS does. Also, when th

Well I may be ignorant also, but as far as I can tell lme4/lmer doesnt have ANY options to specify the variance-covariance matrix while SPSS does. Also, when the number of within subject levels are few, I often find that using the classic repeated measures approach, but estimating using ML/REML (to handle random missing data) on a specified (or unstructured) covariance-variance matrix to be more powerful and/or more likely to converge while accounting for important dependences than mixed models using random effects...SPSS does this kind of analysis easily, but I havent found any equivalent packave in R.