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st: Multilevel Poisson with constraints


From   Jibonayan Raychaudhuri <jibonayanrc@yahoo.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: Multilevel Poisson with constraints
Date   Tue, 16 Aug 2011 00:31:36 -0700 (PDT)

Hi Statalist Users,


I am estimating a Multilevel poisson model in Stata. Basically, I am modelling the number of
visits to different  recreational sites as a function of a host of explanatory variables. I have two 

queries regarding my model:

(1) There is a theoretical justification for modelling  the dependent variable as a
logarithmic function  of one of the independent variables. The model that I estimated is as follows:

xtpoisson
nvisits x1 x2 x3 log(x4) x5, i(site) normal

However given that this is Poisson model, I am not sure how to interpret the coefficient of
x4.

(2) I would like to impose an inequality constraint on the estimated coefficients of x1 and x2
viz., _b[x1]+_b[x2]>=0 
Will that be possible to do in xtpoisson? If yes, how?


Any help will be much appreciated.

Best,
Jibonayan

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