In the Long & Freeze book published by  Stata, the authors estimate a Poisson 
regression model using the constraint  command to control for unequal 
exposure. It produces the same coefficients as  when using exposure or offset, but 
the pseudo-R^2 value is substantially larger  when using the constraint option 
(p. 265). However, when I use the constraint  option, Stata does not produce a 
pseudo-R^2 value. Does anyone know whether  there has been a change made to 
the program by Stata?
Thanks in  advance.
Bob Kaminski  
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