I haven't been an R lister for a bit, but I hope to enlist someone's help here. I think this is a simple question, so I hope the answer is not much trouble. Can you please respond directly to this email address in addition to the list (if responding to the list is warranted)? I have a histogram and I want to see if the data fit a Poisson distribution. How do I do this? It is preferable if it could be done without having to install any or many packages. I use R Version 1.12 (1622) on OS X Thank-you very much, Tom Isenbarger -- Tom Isenbarger PhD isen@plantpath.wisc.edu 608.265.0850 [[alternative HTML version deleted]]
Thomas Isenbarger <isen <at> plantpath.wisc.edu> writes:> > I haven't been an R lister for a bit, but I hope to enlist someone's > help here. I think this is a simple question, so I hope the answer > is not much trouble. Can you please respond directly to this email > address in addition to the list (if responding to the list is > warranted)? > > I have a histogram and I want to see if the data fit a Poisson > distribution. How do I do this? It is preferable if it could be > done without having to install any or many packages. > > I use R Version 1.12 (1622) on OS X > > Thank-you very much, > Tom Isenbarger > > -- > Tom Isenbarger PhD > isen <at> plantpath.wisc.edu > 608.265.0850 > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help <at> stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > >by "histogram" do you mean that you have counts for each non-negative integer? or are the data more binned than that? (I'll assume the former since it's slightly easier to deal with.) Say you have vectors "number" and "count". The mean of the sample is meanval <- sum(number*count). The _expected_ number of counts in each bin if the distribution is Poisson is expval <- sum(count)*dpois(number,meanval). The chi-square statistic is csq <- sum((expval-count)^2/expval), with df <- length(count)-2 degrees of freedom (for the mean and the total number of observations). pchisq(csq,df=df,lower.tail=FALSE) should give you the chi-squared probability. A couple of minor issues: (1) beware, this is shooting from the hip -- haven't tested at all; (2) you may have to deal with lumping categories (rule of thumb is that expected number of counts in a bin should not be < 5). Other ways to tackle this: use fitdistr() from MASS with different candidate distributions (Poisson, neg. bin.) and do a likelihood ratio test or compare AICs; compare variance and mean of distribution (much cruder). See http://www.zoo.ufl.edu/bolker/emd/probs/ED-4.1.html for a worked example of a similar problem.
See ?goodfit in package vcd. On 7/20/05, Thomas Isenbarger <isen at plantpath.wisc.edu> wrote:> I haven't been an R lister for a bit, but I hope to enlist someone's > help here. I think this is a simple question, so I hope the answer > is not much trouble. Can you please respond directly to this email > address in addition to the list (if responding to the list is > warranted)? > > I have a histogram and I want to see if the data fit a Poisson > distribution. How do I do this? It is preferable if it could be > done without having to install any or many packages. > > I use R Version 1.12 (1622) on OS X > > Thank-you very much, > Tom Isenbarger > > > -- > Tom Isenbarger PhD > isen at plantpath.wisc.edu > 608.265.0850 > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html >
Hi,
see:
http://cran.r-project.org/doc/contrib/Ricci-distributions-en.pdf
Regards,
Vito
Thomas Isenbarger isen at plantpath.wisc.edu
wrote:
I haven't been an R lister for a bit, but I hope to
enlist someone's
help here. I think this is a simple question, so I
hope the answer
is not much trouble. Can you please respond directly
to this email
address in addition to the list (if responding to the
list is
warranted)?
I have a histogram and I want to see if the data fit a
Poisson
distribution. How do I do this? It is preferable if
it could be
done without having to install any or many packages.
I use R Version 1.12 (1622) on OS X
Thank-you very much,
Tom Isenbarger
--
Tom Isenbarger PhD
isen at plantpath.wisc.edu
608.265.0850
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I would first reccomend you to update your version of R. Then download the libraries rmutil and gnlm from Jim Lindsey at http://www.luc.ac.be/~jlindsey/rcode.html decompress and store the files in your "library" folder. Sorry but you will have to donwload a package unless you seriously want to re-invent the wheel. Finally try library(gnlm) ?fit.dist() Cheers Francisco>From: Thomas Isenbarger <isen at plantpath.wisc.edu> >To: r-help at stat.math.ethz.ch >Subject: [R] poisson fit for histogram >Date: Wed, 20 Jul 2005 10:40:51 -0500 > >I haven't been an R lister for a bit, but I hope to enlist someone's >help here. I think this is a simple question, so I hope the answer >is not much trouble. Can you please respond directly to this email >address in addition to the list (if responding to the list is >warranted)? > >I have a histogram and I want to see if the data fit a Poisson >distribution. How do I do this? It is preferable if it could be >done without having to install any or many packages. > >I use R Version 1.12 (1622) on OS X > >Thank-you very much, >Tom Isenbarger > > >-- >Tom Isenbarger PhD >isen at plantpath.wisc.edu >608.265.0850 > > > [[alternative HTML version deleted]] > >______________________________________________ >R-help at stat.math.ethz.ch mailing list >https://stat.ethz.ch/mailman/listinfo/r-help >PLEASE do read the posting guide! >http://www.R-project.org/posting-guide.html