On 18 Sep 2005, at 16:04, Douglas Bates wrote: > You are correct that good documentation of the capabilities of lmer > does not currently exist. lmer is still under active development and > documentation is spread in several places. The vignette in the mlmRev > package explores some of the capabilities of lmer. Also see the > examples in that package.
Yes. Thanks for this, and indeed for the development of the package. I'm currently trying to do GLMMs (binary response), so I thought that I should learn mixed modelling using a library with these capabilities. > You are correct that the denominator degrees of freedom associated > with terms in the fixed effects is different between lme and lmer. > ... > Some arguments on > degrees of freedom can be made for nested grouping factors but the > question of testing fixed effects terms for models with partially > crossed grouping factors is difficult. Would it not be possible to recognise when the model is fully nested, and make this a special case? I was imagining using lmer as a replacement for lme, so finding that they differ in this way came as some surprise. When learning to use a new, relatively undescribed routine, I usually try to see if I can reproduce known results. This is where I was coming unstuck when trying to reproduce lme results using lmer. I suspect that many people (I know of one other in my group) will use lmer as a drop-in replacement for lme specifically for its GLMM capabilities rather than for its partial nesting. I realise, however, that this might not be your priority. > This area could be a very fruitful research area for people with > strong mathematical and implementation skills. That's not me, I'm afraid. I am only just working through Chapter 1 of your (excellent) "mixed effects models in S" book. > There are already some facilities for lmer models such as mcmcsamp and > simulate which can be used for evaluating the posterior distribution > of a single coefficient or for a parametric bootstrap of the reference > distribution of a quantity like the likelihood ratio statistic for a > hypothesis test. This, again, is beyond me at the moment. But I do hope that someone else can respond to the call, especially for "textbook" as well as more complex examples of lmer usage. Best wishes Yan Wong ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
