topic Re: Fitting Poisson density function to a HISTOGRAM(SAS-9.2) in Statistical Procedures

Fitting Poisson density function to a HISTOGRAM(SAS-9.2)

robertrao — Tue, 14 Aug 2012 19:28:01 GMT

Hi everyone,

I am new to this forum. I have been learning SAS for 6 months now. I work in a university. My Question is:

I have two variables:

1)Length of stay

2)specific codes(example : 500, 501 etc)

and for each code there are many patients whose length of stay varies like shown below.

example:

LOS(days) Code

4 500

3 500

7 501`

2 200

8 501

10 501

12 501

etc

etc..........

The question is to make a histogram for LOS(on X-axis) and fit the distribution into a poisson density function and determine Lambda.

I tried to google some information and could not find a solution to this on SAS 9.2 version....

Could you help me in building the code please

Re: Fitting Poisson density function to a HISTOGRAM(SAS-9.2)

StatDave — Thu, 30 Aug 2012 16:53:48 GMT

You can use PROC GENMOD to estimate the poisson mean (lambda). For example, using the portion of data you provided:

data a;

input LOS Code;

datalines;

4 500

3 500

7 501

2 200

8 501

10 501

12 501

;

proc genmod;

model los = / dist=poisson;

estimate 'lambda' intercept 1;

run;

The intercept reported (1.8827) is the estimated log mean. So, exp(1.8827)=6.57 is the estimated poisson mean. Assuming you'll want a confidence interval, the ESTIMATE statement merely repeats the estimate of the intercept which provides the mean estimate and confidence limits (4.92, 8.77).

A histogram of the observed data can be done using the HISTOGRAM statement in PROC UNIVARIATE:

proc univariate noprint;

var los;

hist los;

run;

Re: Fitting Poisson density function to a HISTOGRAM(SAS-9.2)

robertrao — Thu, 30 Aug 2012 17:17:08 GMT

Thanks for your help Dave,

After i fit the poisson density how can i find the chi sqaure goodness of fit on that?

Re: Fitting Poisson density function to a HISTOGRAM(SAS-9.2)

Rick_SAS — Thu, 30 Aug 2012 17:19:11 GMT