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...andom effects nested within levels of a random effect? The problem is this: I have a sample of classes (class being the nesting factor). Within each class I have a sample of students. I have separate random effects models at each level. That is, at the class level, I have: random=~class_size+number_teachers+class_length and at the student level I have: test_score~treatment+experience+age. What I want o assess is the contribution of class level variables simultaneously with individual level variables on test scores. Now, my problem is specifying them both as a random effect. I tried to use:...