[R] Changing the order of the factors in a cumulative logit model
marc_schwartz at me.com
Mon Jun 26 15:55:00 CEST 2017
> On Jun 26, 2017, at 7:52 AM, Eva Wanek <eva.maria.wanek at gmail.com> wrote:
> Hi all,
> I am using the clm function from the ordinal package to fit a cumulative
> logit model. If I run the regression without formatting my dependent
> variable (which is a factor), it works fine, however I need to change the
> order of the factors to be able to interpret the estimates. I have tried
> doing this using the relevel function and the factors are now in the
> correct order, but when running the regression now, I get this:
> Warning message:(1) Hessian is numerically singular: parameters are
> not uniquely determined
> In addition: Absolute convergence criterion was met, but relative
> criterion was not met
> Why is this and what can I do about it?
Without seeing your data or a small data sample that replicates the problem:
I would check for:
1. Structural zeros in the cross tabulation of your dependent variable (DV) and your independent variable[s] (IVs).
2. Perfect prediction between your DV and IVs.
3. "Small" sample size in one or more of your DV levels.
If changing the ordering of your DV levels results in the error, you may have one or more of the above going on in one or more of your DV levels, especially if you shift one or more levels to the extremes (e.g first or last level).
How you handle this may depend upon domain subject matter knowledge and how to deal with possibly collapsing zero or low sample size categories and how that affects the relevance/applicability of the model.
More information about the R-help