Poisson Distribution fitting
On Thu, 25 Aug 2005, Mark Miller wrote:
I am trying to fit a number of distributions to a set of data, I have used the fitdristr() funtion for most of the distributions, but Poisson is not one of the possible distributions. I found somewhee talking about using the gamlss package, but have been unable to find it again, any help would be greatly appreciated.
If you mean fitdistr in package MASS, it can be used. But the mle for a Poisson is just the sample mean.
x <- rpois(250, 2.6) mean(x)
[1] 2.62
fitdistr(x, dpois, list(lambda=2))
lambda 2.6203125 (0.1023841) You can even find the s.e. via mu/sqrt(n), here
mean(x)/sqrt(250)
[1] 0.1657033
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595