[R] About poisson distribution fitting and testing

Spencer Graves spencer.graves at pdf.com
Sun Apr 23 06:04:20 CEST 2006

	  The easiest, general function in R that I know for fitting 
distributions is "fitdistr" in library(MASS).  However, for Poisson, I 
might also try "glm(y~1, family = poisson, ...)".  Regarding testing for 
goodness of fit, I just got 44 hits for RSiteSearch("goodness of fit to 

	  hope this helps.
	  spencer graves	
p.s.  My reply might have been more informative if you had provided 
example data.  For example, for the Poisson, the theoretical variance 
equals the mean.  Clearly, if the sample mean and variance are 6 and 11, 
that alone could raise questions about the adequacy of the Poisson 
assumption, depending on the sample size.

Linda Lei wrote:

> Hi All,
> I have a sequence of positive integers, which is right skewed. The mean
> value is 6 and variance is 11. 
> I suspect it can be fitted by poisson distribution. But I'm not familiar
> with the function to fit distribution. 
> Could you please help me with it? Also, once I fit the poisson 
> distribution, how can I check the good-ness of this fitting?
> Thank you!
> 	[[alternative HTML version deleted]]
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