I have monthly data for events for which I'd like to ensure a good fit for monthly rates to a poisson distribution. The data looks like this:
Month Number_of_events Patient_days Events rate per_1000_patient_days
Jan2016 125 500 250
Feb2016 150 523 286.80
etc.....
I am plotting the monthly rates on a control chart and want to ensure I am meeting the assumption that the underlying distribution is a poisson distribution, otherwise the control limits I've calculated are not valid. I believe I need to use proc genmod to model number_of_events and use the log of patient_days but want to make sure I am not missing anything. Any advice is greatly appreciated!
What have you tried so far?
I've tried something like this:
data a;
set a;
log_pt_days= log(patient_days);
run;
proc genmod data = a;
model number_of_events/ dist = poi offset = log_pt_days;
run;
There are plenty of articles on fitting Poisson distributions like
http://blogs.sas.com/content/iml/2012/04/04/fitting-a-poisson-distribution-to-data-in-sas.html
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