RE: st: Predicted probabilities after mlogit

["Jun Xu" <mystata@hotmail.com>]

An additional note that applies to all nonlinear models:

E(g(x)) != g(E(x)) [the expectation of a nonlinear function of random 
variable is not equation to the function of the expectation of random 
variables

I think what you did with predict is E(g(x)), and what prvalue does is 
g(E(x))



Jun Xu
Ph.D. Candidate
Department of Sociology
Indiana University at Bloomington






> From: "Little, Allan" <a.little@lancaster.ac.uk>
> Reply-To: statalist@hsphsun2.harvard.edu
> To: <statalist@hsphsun2.harvard.edu>
> Subject: st: Predicted probabilities after mlogit
> Date: Mon, 5 Sep 2005 16:10:36 +0100
>
> Dear all,
>
> I'm trying to calculate predicted probabilities following a multinomial 
> logit regression. My dependant variable has three states - employment 
> (coded 0), unemployment (1) and inactivity (2).
>
> I would like to calculate the predicted probability, firstly evaluated at 
> the mean, and secondly evaluated a number of different specified values. 
> However, I am encountering some apparent inconsistencies according to which 
> command I use.
>
> 1. If I use 'predict p0 p1 p2 if e(sample)' [option 'pr' is assumed to be 
> the default]. The predicted probabilities are equivalent to the proportion 
> (sample mean) for each category.
>
> 2. If I use the 'prvalue' command, the predicted probabilties are different 
> to the above (for example, the predicted probability of being employed is 
> much higher than the sample proportion of people who are actually 
> employed).
>
> 3. Similarly, the value given by 'mfx compute, predict(pr outcome(0))' also 
> gives a predicted probability which is the same as the value from 
> 'prvalue', but different to the 'predict' command.
>
> Could anyone explain the difference between the predicted probabilities 
> given by the prvalue, predict and mfx commands? I believe that the 
> predicted probability (evaluated at the mean values of X) should be 
> equivalent to the sample proportion in each category - am I right?
>
>
> Thanks for your time,
> Allan Little
> Lancaster University
>
>
>
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