"Non-positive definite approximate variance-covariance" output
The standard errors are for the fixed-effects parameters. The apVar component includes approximate variances of the estimators of (functions of) the variance components, which is where the positive-definiteness failure may be occurring..
On Wed, Feb 17, 2016 at 2:28 PM Jacob Bukoski <jbukoski1 at gmail.com> wrote:
Hi all, I was in a discussion with my advisor today, and the issue of "non-positive definite approximate variance-covariance" errors in R when using the lme() function arose. Depending on the varFunc specification that I use, I receive the "non-positive definite approximate variance-covariance" output when calling myModel$apVar -- however, there are standard errors returned for my model coefficients in the model summary. My understanding is that if the variance-covariance cannot be approximated, neither should the standard errors... how is the lme() function returning standard errors without a variance-covariance approximation? Many thanks, Jacob -- Jacob J. Bukoski Master of Environmental Science Candidate, 2016 School of Forestry and Environmental Studies, Yale University jbukoski1 at gmail.com | jacob.bukoski at yale.edu | LinkedIn < https://www.linkedin.com/profile/view?id=AAIAAAdWVW8BMzqU_2EGNbEkyuy8O7K1Jyhd8ps&trk=nav_responsive_tab_profile_pic
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