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# st: Re: pprob

 From Stephen Sullivan To statalist@hsphsun2.harvard.edu Subject st: Re: pprob Date Sat, 2 Oct 2010 09:33:13 -0400

```Hello.
I have a dataset, which does not appear to fit the Poisson distribution.
I then ran glm and nbreg commands as suggested (http://www.ats.ucla.edu/stat/stata/library/count.htm).
To see how the my variable fit the Poisson and negative binomial distributions, I downloaded and used the nbvargr command.
Nevertheless, something seems strange as all pprob values for the Poisson are 0.

The output is:
. nbvargr total

Obtaining Parameter Estimates

(9 observations deleted)
here

Negative Binomial Probabilities
with mean = 47.92857 & overdispersion = .0867781

+------------------------------+
|  k       nbprob        nbcum |
|------------------------------|
1. |  0   0.00000001   0.00000001 |
2. |  1   0.00000006   0.00000006 |
3. |  2   0.00000029   0.00000035 |
4. |  3   0.00000105   0.00000140 |
5. |  4   0.00000307   0.00000446 |
|------------------------------|
6. |  5   0.00000767   0.00001214 |
7. |  6   0.00001703   0.00002917 |
8. |  7   0.00003438   0.00006355 |
9. |  8   0.00006417   0.00012772 |
10. |  9   0.00011222   0.00023994 |
|------------------------------|
11. | 10   0.00018568   0.00042562 |
+------------------------------+
k was byte now float

Poisson Probabilities for lambda = 47.92857

+------------------------------+
|  k        pprob         pcum |
|------------------------------|
1. |  0   0.00000000   0.00000000 |
2. |  1   0.00000000   0.00000000 |
3. |  2   0.00000000   0.00000000 |
4. |  3   0.00000000   0.00000000 |
5. |  4   0.00000000   0.00000000 |
|------------------------------|
6. |  5   0.00000000   0.00000000 |
7. |  6   0.00000000   0.00000000 |
8. |  7   0.00000000   0.00000000 |
9. |  8   0.00000000   0.00000000 |
10. |  9   0.00000000   0.00000000 |
|------------------------------|
11. | 10   0.00000000   0.00000000 |
+------------------------------+
(11 observations deleted)

Any thoughts on what I may have done wrong?
Why all the zeros for the poisson prob?
Do I need to somehow install pprob?

Stephen
Stephen R. Sullivan, MD, MPH
Assistant Professor, Surgery and Pediatrics
Brown University
Plastic Surgery
Rhode Island and Hasbro Children's Hospitals
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```