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
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