R help - Feb 2010 - Goodness of fit test for count data

Dear  all, 

I am trying to test goodness of fit. I assume that a data follow Poisson or
Negative binomial distribution. I can test the goodness of fit in case of no
truncated data. However, I could not find any good function or packages when
a data is truncated.  

For example, a frequency table for the number of visiting emergency room in
one hundred one observations past one year is as follow: 
N freq 
1 30 
2 35 
3 26 
4 8 
5 0 
6 2 
7 0 

 I expect the frequency table to satisfy a Poisson distribution or Negative
binomial distribution. However, the distribution is different from the usual
Poisson or Negative binomial distribution because one value, zero, is
excluded. I expect that the distribution is zero truncated distribution. 

In case of SAS, I used NLMIXED procedure to calculate the expected
probability when y=1 ? y=n under the assumption that a data follows Poisson
or Negative binomial distribution. And then I run Chi-square test. If you
need the SAS code, I will send E-mail.
I want to run this test in R.
Could you suggest any idea that can I perform this test in R.

Have a nice day.

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You can compute the conditional probability that your variable equals k given
that it is non-zero. For example, if X has poisson distribution with parameter
lambda then
P(X=k/X!=0) = P(X=k)/(1-P(X=0)) = (exp(-lambda)/(1-exp(-lambda))*lambda^k/k!
Now you can find lambda for which the sum of squares of your errors is minimal
and then use CHi-aquared test using these expected frequencies.

Similarly for negative binomial distribution.

--- On Tue, 23/2/10, pinusan <anhong at msu.edu> wrote:
> From: pinusan <anhong at msu.edu>
> Subject: [R] Goodness of fit test for count data
> To: r-help at r-project.org
> Received: Tuesday, 23 February, 2010, 6:11 AM
> 
> Dear? all, 
> 
> I am trying to test goodness of fit. I assume that a data
> follow Poisson or
> Negative binomial distribution. I can test the goodness of
> fit in case of no
> truncated data. However, I could not find any good function
> or packages when
> a data is truncated.? 
> 
> For example, a frequency table for the number of visiting
> emergency room in
> one hundred one observations past one year is as follow: 
> N freq 
> 1 30 
> 2 35 
> 3 26 
> 4 8 
> 5 0 
> 6 2 
> 7 0 
> 
>  I expect the frequency table to satisfy a Poisson
> distribution or Negative
> binomial distribution. However, the distribution is
> different from the usual
> Poisson or Negative binomial distribution because one
> value, zero, is
> excluded. I expect that the distribution is zero truncated
> distribution. 
> 
> In case of SAS, I used NLMIXED procedure to calculate the
> expected
> probability when y=1 ? y=n under the assumption that a
> data follows Poisson
> or Negative binomial distribution. And then I run
> Chi-square test. If you
> need the SAS code, I will send E-mail.
> I want to run this test in R.
> Could you suggest any idea that can I perform this test in
> R.
> 
> Have a nice day.
> 
> -- 
> View this message in context:
http://n4.nabble.com/Goodness-of-fit-test-for-count-data-tp1564963p1564963.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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