R help - Sep 2012 - Zero inflated Models- pscl package

Dear R users, 

I want to apply zero inflated models with continuous and categorical
variables and I used pscl package from R and the zeroinf() function. My
question are the follow:

a) The value of fitted.values is mu or (1-p)*mu? where p is the probability
of zero came form a zero point mass

b) If mu is zero, how do i know if it is a zero from the zero point mass or
from the count process?  

Thank you so much in advance.
Filipa J.



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On Mon, 10 Sep 2012, Filipa J. wrote:
> Dear R users,
>
> I want to apply zero inflated models with continuous and categorical 
> variables and I used pscl package from R and the zeroinf() function. My 
> question are the follow:
>
> a) The value of fitted.values is mu or (1-p)*mu? where p is the 
> probability of zero came form a zero point mass
See vignette("countreg", package = "pscl"), especially
Appendix C.

The default predict(..., type = "response") and fitted(...) both
compute
the expected value Equation (8). This corresponds to your (1-p)*mu but 
uses a different notation.
> b) If mu is zero, how do i know if it is a zero from the zero point mass 
> or from the count process?
You can inspect all component: Your "mu" ("exp(x'b)" in
the notation of
the paper) can be computed with predict(..., type = "count") and
"p" ("pi"
in the paper) with predict(..., type = "zero").

Best,
Z