Suggestions? -- Yes. 1) Wrong list.. Post on R-sig-mixed-models, not here.
2) Follow the posting guide and provide the modelformula, which may well be the source of the difficulties (overfitting). -- Bert On Fri, Dec 16, 2011 at 1:56 PM, Scott Raynaud <scott.rayn...@yahoo.com> wrote: > I'm using an R program (which I did not write) to simulate multilevel data > (subjects in locations) used in power calculations. It uses lmer to fit a > mixed logistic model to the simulated data based on inputs of means, > variances, slopes and proportions: > > (fitmodel <- lmer(modelformula,data,family=binomial(link=logit),nAGQ=1)) > > where modelformula is set up in another part of the program. Locations are > treated as random and the model is random intercept only. The program is > set to run 1000 simulations. > > I have temperature, five levels of gestational age (GA), birth wieght (BW) > and four > other categorical pedictors, all binary. I scaled everything so that all my > slopes are in the > range of -5.2 to 1.6 and variances from .01 to .08. I have a couple of > categories > of GA that have small probabilities (<.10). I'm using a structured sampling > approach > looking at 20, 60, 100, and 140 locations with a total n=75k. The first > looks like this: > > # groups n > 5 800 > 4 2239 > 3 3678 > 3 5117 > 3 6557 > 2 7996 > Total 20 75000 > > As the level 2 sizes increase, the cell sizes decrease. When I run this > model in > the simulation I get: > > Warning: glm.fit: algorithm did not converge > > every time the model is fit (I killed this long before it ran 1000 times). > > I tried increasing the number of iterations to no avail. I suspected linear > dependencies among the predictors, so I took out GA (same result), put > GA back and took out BW (same result) and then took out both GA and > BW. This ran about half the time with th other half passing warnings > such as: > > Warning: glm.fit: algorithm did not converge > Warning: glm.fit: fitted probabilities numerically 0 or 1 occurred > > or > > Warning: glm.fit: fitted probabilities numerically 0 or 1 occurred > > in addition to some like the original warning. > > If I leave everything in but temperature, then it runs fine. I also tested > the full > model separately at 50 and 75 level 2 units each with total n=75k. Nothing > converged. > > I want to include temperature, but I'm not sure what else to try. Any > suggestions? > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.