Convergence warnings in lme4
On 14-10-21 09:21 AM, adam.hayward at ed.ac.uk wrote:
Dear list users, This is a general question, rather than a specific example of my data. I have recently upgraded my computer and to R ver 3.1.1 from 3.0.2. Models (glmer) which previously ran perfectly are now producing warning messages regarding failure to converge, for example: Warning messages: 1: In checkConv(attr(opt, "derivs"), opt$par, ctrl = control$checkConv, : Model failed to converge with max|grad| = 0.0238312 (tol = 0.001, component 13) 2: In checkConv(attr(opt, "derivs"), opt$par, ctrl = control$checkConv, : Model failed to converge: degenerate Hessian with 1 negative eigenvalues and this is true with a range of optimizers. Running identical models on my old and new versions of R produces identical output (estimates, AIC etc) but the new version of lme4 produces the warnings. My questions are thus (1) has lme4 recently been updated with significant changes in what constitutes acceptable convergence, and (2) can my models now be trusted? Many thanks for any comments or help, Adam
Presumably you're using version 1.1-7 (the latest version on CRAN); it would be helpful to know that. You can see changes to lme4 at http://cran.r-project.org/web/packages/lme4/news.html . The significant changes you're referring to started in version 1.1-3. We are still working to figure out how to get the right level of sensitivity and specificity on these tests; we haven't come up with anything definitive yet. I've got an example of various attempts at troubleshooting (restarting the fit from the same point, trying different optimizers, etc.) posted at http://rpubs.com/bbolker/lme4trouble1 . The bottom line is that your models are no more nor less trustworthy than they used to be. If you have tried them with a variety of optimizers, and if the results make sense, it's *probably* the case that they're OK, and just a little unstable. Ben Bolker