# Why is the McFadden pseudo-R2 different between a fit with polr and the corresponding model using vglm

If I calculate the McFadden pseudo-R2 using 1- (LLf/LL0)

LLf   <- logLik(Model) #full model
LL0   <- logLik(Model.0) #model with intercept only.


Why do I get different results if the model is fit with polr (MASS package) and with vglm (VGAM) using family=propodds.

For polr =

LLf = -6973.556 (df=16) LL0 = -9691.214 (df=3) R2 = 0.2804249

For vglm =

LLf = -1233.347 LL0 = 3951.005 R2 = 0.6878397

I don't understand why the log likelihood would go up by fitting polr and down using vglm?

I assumed I reversed something, but it seems not.

Fitted coefficients and standard errors are equal between the two models. AIC is completely different, but I imagine this is expected. I also notice the intercepts have reversed values, which seems strange. I cannot get vglm to generate a model with the "correct" intercepts.

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I cannot reproduce the different LL values for polr() and vglm(), do you have a minimum reproducible example? With regard to the different intercepts: Both are correct, they just belong to different ways of parametrizing the ordinal regression - see this answer. –  caracal Feb 20 at 20:25