On Mon, 2 Feb 2009, antonio.gasparr...@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.
See
?dpois
And for the inner workings, see
stats:::logLik.glm
poisson()$aic
---
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/
HTH,
Chuck
Example:
I simulate 20 observations from a Poisson distribution with mean 800.
y <- rpois(20,800)
model <- glm(y ~ 1, family=poisson())
logLik(model)
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/ )
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cbe...@tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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