Hi. How can i link two variables, so when i group the first i group also the second one? I try whit create a model matrix (model.matrix) and use a grouping function like "balancedGrouped(nlme)". More specific i have varx:AGE and vary(binomial):o (dead),1(alive). I want to create age group,link vary group, compute the mean of x link the mean of y. Thank you. Michele.