On Tue, 2006-06-20 at 20:27 +0200, Göran Broström wrote: > On 6/19/06, Rick Bilonick <[EMAIL PROTECTED]> wrote: > > On Sun, 2006-06-18 at 13:58 +0200, Douglas Bates wrote: > > > If I understand correctly Rick it trying to fit a model with random > > > effects on a binary response when there are either 1 or 2 observations > > > per group. > > If you look at Rick's examples, it's worse than that; each group > contains identical observations (by design?). > > May I suggest: > > > glm(y ~ x, family = binomial, data = unique(example.df)) > > I think lmer gives a very sensible answer to this problem. > > Göran > The paired responses happen to be always the same in the data set that I have. My understanding is that they could differ, but rarely do. For the particular single independent variable, it will always be the same for each observation for a given subject. So I essentially have 2n observations where there are n unique results. However, I want to add additional independent variables where the measurements differ within a subject (even though the response within the subject is the same).
I ran glm on the n subjects and the 2n for lmer and get similar estimates and se's but not identical. With just one independent variable where the observations are identical in each cluster, lmer gives slightly smaller se's using all 2n. When I include a second independent variable that varies within each subject, lmer gives larger standard errors, about 25% larger for the independent variable that doesn't vary within subjects and just slightly larger for the one that does vary. I could create a data set where I take all subjects with just one observation per subject and then randomly select one observation from each pair for subjects who have both observations. But I'd rather not have to randomly remove observations. I would expect that when the responses and independent variable are the same within each subject for all subjects, the residual error must be zero after you account for a random effect for subjects. Rick B. ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html