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I'm working on estimating a generalized estimating equation in R. I have a multinomial (ordinal) outcome, and so I have been attempting to use the package multgee since, as far as I know, packages like geepack or gee don't allow for the estimation of multinomial outcomes.

However, I'm running into some issues. The documentation seems good, but in particular, it seems to be requiring initial (starting) values in the model. If I try to run the model without it, I get a line requesting starting values. Here's the model:

formula <- PAINAD_recode~Age + Gender + group_2part + Cornell + stim_intensity_scale

fitmod <- ordLORgee(formula,data=data,bstart=c(1,0,1,0,1),id=data$subject,
                repeated=data$trial)

I just threw in some ones and zeroes for the starting values there. However, when I enter starting values (even plausible ones), it claims that:

Starting values and parameters vector differ in length

I thought that with five predictors, I would need five starting values. I can't find more information about this particular matrix. Does anyone have any thoughts on this? The outcome here has five levels (ordinal) and the repeated component has 20 levels. ANy suggestions would be appreciated.

Jess A.
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  • Any chance that the fifth parameter is "aliased", i.e. it is entirely determined by the other four? – IRTFM Aug 05 '14 at 21:28
  • Yeah, that's what I thought as well, but I tried it with four starting values and that doesn't work either. – Jess A. Aug 05 '14 at 21:45

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