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06-08-2016 10:13 PM

Can anybody please let me know how to calculate P value for a Poisson distribution? Thanks.

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06-09-2016
09:49 PM

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Posted in reply to Reeza

06-09-2016 09:47 PM

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Posted in reply to ali_siddiquee

06-08-2016 10:30 PM

I believe that is using the CDF, cumulative distribution function.

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06-09-2016
09:49 PM

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Posted in reply to Reeza

06-09-2016 09:47 PM

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Posted in reply to ali_siddiquee

06-10-2016 06:19 AM

You accidentally marked your own replay as the solution.

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Posted in reply to ali_siddiquee

06-09-2016 06:41 AM

If you have an observed value of some test statistics that follows a Poisson distribution, then Reeza is correct and you can use the CDF function:

lambda=10; obsValue=15;

OneSidePVal = 1 - cdf("Poisson", ObsValue, lambda);

However, since most statistics do not follow a Poisson distribution, maybe you are asking about fitting a Poisson distribution to data and obtaining a p-value for the goodness-of-fit test? In that case, you should use PROC GENMOD to fit the distribution as shown in the article "Fitting a Poisson distribution to data in SAS". (You can also use COUNTREG.)

Unfortunately, the statistics that come out of PROC GENMOD do not include p-values, but you can use PROC FREQ to compute a chi-square statistics that compares the observed and expected values in each category. The details are shown in the article "Testing the fit of a discrete distribution." If you are interested, there are also graphical techniques for evaluating the fit.

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Posted in reply to Rick_SAS

06-09-2016 09:51 PM

Thank you so much. Really appreciate. Best regards.