st: fitted values in xtmepoisson and xtpoisson

[Dan MacNulty <macn0007@umn.edu>]

Dear Statalist,
According to the STATA 10 documentation re:longitudinal/panel data 
(p.264) the model specified as:

   xtmepoisson seizures treat lbas lbas_trt lage visit || subject:

...is equivalent to this model:

   xtpoisson seizures treat lbas lbas_trt lage visit, re

Yet, the population-averaged fitted values (i.e., predictions that 
include only the fixed portion of the model) appear to differ 
substantially between the two models. For the xtmepoisson model, I 
generated these with the post-estimation command:

   predict newvar, fixedonly

For the xtpossion model, I generated the population-averaged fitted 
values with the post-estimation command:

   predict newvar, nu0

I'd be very grateful if someone could explain why there's an apparent 
difference in the population-averaged fitted values between these two 
purportedly equivalent models.

thanks,
Dan MacNulty







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