[R] logLik for poisson models
Charles C. Berry
cberry at tajo.ucsd.edu
Mon Feb 2 05:32:22 CET 2009
On Mon, 2 Feb 2009, Antonio.Gasparrini at lshtm.ac.uk wrote:
> Dear all,
> I have a very basic question:
> how does the logLik function work for poisson models?
You mean its inner workings or just what is the computation?
The computation is just the vanilla loglikelihood:
sum( dpois( y, mean(y), log=TRUE) )
for your Poisson model.
And for the inner workings, see
More generally, read the article
Ligges, U. (2006): R Help Desk: Accessing the Sources. R News 6
(4), 43-45. http://cran.r-project.org/doc/Rnews/
> I simulate 20 observations from a Poisson distribution with mean 800.
> y <- rpois(20,800)
> model <- glm(y ~ 1, family=poisson())
> I would like to know what's the exact formula the function logLik uses.
> I looked at ?extractAIC but I cannot sort it out.
> Can you please give me an help?
> Thanks a lot
> Antonio Gasparrini
> Public and Environmental Health Research Unit (PEHRU)
> London School of Hygiene & Tropical Medicine
> Keppel Street, London WC1E 7HT, UK
> Office: 0044 (0)20 79272406 - Mobile: 0044 (0)79 64925523
> Skype contact: a.gasparrini
> http://www.lshtm.ac.uk/people/gasparrini.antonio ( http://www.lshtm.ac.uk/pehru/ )
> R-help at r-project.org mailing list
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
More information about the R-help