1. M

    xtmixed covariances: why it doesn't work??

    Hi, I'm trying for weeks to run the following model: mi estimate, variance : xtmixed MathG5 MathG4 , || classID:, covariance(unstructured) || studentID: , covariance(unstructured) This is only the first model, I want to add a lot more covariates and interaction effects, but if the first...
  2. P

    Multi-level models: xtmixed vs. xtreg, re

    Hi all, I am dealing with a panel and multi-level data. Specifically, I have data (prices, etc...) related to numerous items (each identified by a unique id) within a product category in a given period. The measurements for the same item are repeated several times in this period: that is, for...