I have some problem with my lienar mixed model.
When I do my model with the maximum likelihood, I have no error. But, when I want the confidence intervals, I get the Error : " cannot get confidence intervals on var-cov components : Non positive definite approximate variance-covariance".
Does that mean my model isn't ok ?
Plus, when I do the same model with "REML", the error is not here anymore. But the AIC is less good and I can't do anova test anymore too ...
What can I do ?
Thanks for your help,