Re: [R-sig-phylo] fitContinuous in geiger: positive log-likelihoods when trait values <1

2011-03-07 Thread Nick Matzke
Ah, so while re-creating my problem for copy-paste-debug goodness on the listserv, I discovered what was confusing me. Originally, when I ran the various models, I got these log-likelihoods for results: == tf2ic2kzkr t

Re: [R-sig-phylo] fitContinuous in geiger: positive log-likelihoods when trait values <1

2011-03-07 Thread Dan Rabosky
Hi Nick- Are you are getting differences in relative AICs between models from simple rescaling (multiplying by a constant)? The actual values of the traits *might* matter for optimization, depending on various parameters associated with optimization (and whatever algorithm is being used - th

Re: [R-sig-phylo] fitContinuous in geiger: positive log-likelihoods when trait values <1

2011-03-07 Thread Nick Matzke
Doh! Really should have remembered that, likelihoods-can-be-greater-than-1 is likelihood 101... I am still a little puzzled by the dramatically different results between rescaling and not, will try to post an example in a sec... On 3/7/11 12:37 PM, Nick Matzke wrote: Hi all, It seems to

Re: [R-sig-phylo] fitContinuous in geiger: positive log-likelihoods when trait values <1

2011-03-07 Thread Liam J. Revell
Nick, Log-likelihoods are calculated as the logarithm of the product of the heights of the probability density function. Since the probability density function must integrate to 1.0, it can have a height that is much greater than 1.0 if all the probability density is concentrated on a small

[R-sig-phylo] fitContinuous in geiger: positive log-likelihoods when trait values <1

2011-03-07 Thread Nick Matzke
Hi all, It seems to be a popular week for questions! I am running fitContinuous on a variety of continuous trait data. I am noticing that when the traits are in units where the max is less than 1 (these are not ratio data, though), many of the various models produce log-likelihoods that are