Despite having read the documentation of the rms::orm() R package for fitting ordinal cumulative probability models, I am unclear on what models are being compared in the model likelihood ratio test that appears in the output. Is this comparing the proportional odds model to an analogous generalized logit non-proportional odds model?
An example of the relevant part of the output of a model of the form
orm(y ~ x1 + x2, data = d) appears below for reference.
Model Likelihood Discrimination Rank Discrim. Ratio Test Indexes Indexes Obs 1463 LR chi2 354.50 R2 0.216 rho 0.471 Distinct Y 19 d.f. 4 g 1.049 Median Y 8 Pr(> chi2) <0.0001 gr 2.856 max |deriv| 1e-08 Score chi2 357.09 |Pr(Y>=median)-0.5| 0.182 Pr(> chi2) <0.0001