stata running very slow

  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...