Different LLRs on multinomial logit models in R and SPSS

S?ren Vogel <sovo0815 <at> gmail.com> writes:

Hello, after calculating a multinomial logit regression on my data, I
compared the output to an output retrieved with SPSS 18 (Mac). The
coefficients appear to be the same, but the logLik (and therefore fit)
values differ widely. Why?

Since constants that are independent of the model
parameters can be left out of a log-likelihood calculation
without affecting inference among models, it is quite common
for likelihoods to be calculated differently in different
software packages (for example, the (n/2 log(2*pi)) constant in the
Gaussian log-likelihood) -- this is true even among different
computations within the R ecosystem.  What's important is the difference
among log-likelihoods between models, which is the same (up to
the numeric precision of what you've shown us) for both
software packages.

135.02-129.8

[1] 5.22

204.2904-199.0659

[1] 5.2245

  Ben Bolker