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st: RE: Poisson Rates


From   "Lachenbruch, Peter" <[email protected]>
To   <[email protected]>
Subject   st: RE: Poisson Rates
Date   Mon, 12 Jan 2009 12:14:35 -0800

I think the best way is to note that a rate is m/exposure.  A Poisson
model fits log(m)=log(exposure)+XB, so you only need to use the offset
feature in Stata.  The command will be
poisson y xvariables, exposure(exposure)
If you use offset, you first need to take ln(exposure)=lex 
poisson y xvariables,offset(lex)

Tony

Peter A. Lachenbruch
Department of Public Health
Oregon State University
Corvallis, OR 97330
Phone: 541-737-3832
FAX: 541-737-4001


-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
[email protected]
Sent: Monday, January 12, 2009 12:01 PM
To: [email protected]
Subject: st: Poisson Rates

I created a poisson model with the number of injuries as the depedent  
variable and age, experience and age*experience as the predictors.
Age and experience are categorical variables. We have a lot of people  
with the similar ages and experience levels so I'm categorizing age  
and experience into 1 year intervals.
My outcome is then the number injuries predicted for each of these  
age/experience groups.
I'm first plotting experience vs the number of predicted injuries by  
various 1-year age categories.
In order to turn the y-axis (counts) into rates can I divide each of  
these 1-year experience groups by the number of hours worked for that  
1-year experience group?
Thanks for your help.

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