Re: [R] Expressing a multinomial GLM as a series of binomial GLMs

2014-07-23 Thread John Fox
Dear Christoph, I don't see how what you suggest can work in a mixed-effects model. In the case you originally raised, of independent observations, you should be able to recover the coefficients for the multinomial logit model by fitting the logits that I suggested in my earlier email, but not

Re: [R] Expressing a multinomial GLM as a series of binomial GLMs

2014-07-23 Thread Christoph Scherber
Dear John and R-helpers, Thanks for your replies that were both very helpful. The reason I was asking is that I´m searching for an easier way to incorporate *random effects* in a multinomial model. I was hoping that *combinations of binomial glmmPQL or lmer calls* might be able to do the job

Re: [R] Expressing a multinomial GLM as a series of binomial GLMs

2014-07-22 Thread Charles Berry
Charles Berry ucsd.edu> writes: > > Scherber, Christoph gwdg.de> writes: > > > > > Dear all, > > > > I am trying to express a multinomial GLM (using nnet) as a series of GLM > models. [deleted] > > Doing the obvious comparison: > > ggen.preds <- > sapply( levels(multicats), >

Re: [R] Expressing a multinomial GLM as a series of binomial GLMs

2014-07-22 Thread John Fox
Dear Christoph, If I understand correctly what you've done, the two approaches are not equivalent and should not in general produce the same fitted probabilities. Letting {a, b} represent logit(a vs. b) = log(Pr(a)/Pr(b)) and {ab, cd} represent logit(a or b vs. c or d), and numbering the respon

Re: [R] Expressing a multinomial GLM as a series of binomial GLMs

2014-07-22 Thread Charles Berry
Scherber, Christoph gwdg.de> writes: > > Dear all, > > I am trying to express a multinomial GLM (using nnet) as a series of GLM models. > > However, when I compare the multinom() predictions to those from GLM, I see differences that I can´t > explain. Can anyone help me out here? > > Here com

[R] Expressing a multinomial GLM as a series of binomial GLMs

2014-07-22 Thread Scherber, Christoph
Dear all, I am trying to express a multinomial GLM (using nnet) as a series of GLM models. However, when I compare the multinom() predictions to those from GLM, I see differences that I can´t explain. Can anyone help me out here? Here comes a reproducible example: ## # set up data: (don´t care