different aic and LL in glmer(lme4) and glimmix(SAS)?
On Thu, Jul 1, 2010 at 2:54 PM, Hadley Wickham <hadley at rice.edu> wrote:
The difference is probably due to the way that the deviance is defined for the binomial family in R. ?A glm family object is a list of functions and expressions. ?One of the functions, called "dev.resids" has arguments y, mu and weights. ?You can specify the response for a binomial family as the 0/1 responses or as a matrix with two columns as you did here. ?When you use the two column specification the response y is transformed to the fraction of successes and the number of cases is incorporated in the weights. ?It turns out that this is all the information necessary for obtaining the mle's of the parameters but it does not give the same deviance as you would get by listing the 0/1 responses.
Isn't it also possible the difference is because (e.g.) lme4 drops constants out of the likelihood and SAS doesn't?
Certainly a possibility. I sometimes amaze myself with how sloppy I can be in derivations. :-)