I am having difficulty to get predicted counts/probabilities with "prvalue"
after fitting a zero-inflated negative binomial regression model. I followed
the method outlined by Long and Freese (2001) "Regression Models for
categorical dependent variables using Stata". Could anyone help me out?
Below are the outputs:
Zero-inflated negative binomial regression Number of obs =
1840
Nonzero obs =
849
Zero obs =
991
Inflation model = logit LR chi2(1) =
6.27
Log likelihood = -4192.23 Prob > chi2 =
0.0122
----------------------------------------------------------------------------
--
adm_days | Coef. Std. Err. z P>|z| [95% Conf.
Interval]
-------------+--------------------------------------------------------------
--
adm_days |
ct_index | -.1282928 .0512773 -2.50 0.012 -.2287944
-.0277912
_cons | -2.78323 .1307951 -21.28 0.000 -3.039584
-2.526876
exposuredays | (exposure)
-------------+--------------------------------------------------------------
--
inflate |
inf_index | 1.15054 .1285382 8.95 0.000 .8986098
1.40247
_cons | -.0008264 .1041639 -0.01 0.994 -.2049838
.2033311
-------------+--------------------------------------------------------------
--
/lnalpha | .7193129 .0893166 8.05 0.000 .5442556
.8943702
-------------+--------------------------------------------------------------
--
alpha | 2.053022 .1833689 1.723325
2.445795
----------------------------------------------------------------------------
--
Vuong test of zinb vs. standard negative binomial: z = 7.48 Pr>z =
0.0000
. prvalue, x(ct_index=0)
zinb: Predictions for adm_days
Predicted rate: .
Predicted probabilities:
Pr(y=0|x,z): . Pr(y=1|x): .
Pr(y=2|x): . Pr(y=3|x): .
Pr(y=4|x): . Pr(y=5|x): .
Pr(y=6|x): . Pr(y=7|x): .
Pr(y=8|x): . Pr(y=9|x): .
Pr(Always0|z): 0.3374
x values for count equation
ct_index
x= 0
z values for binary equation
inf_index
z= -.58580838
Thank you very much,
Wenjun
Wenjun Li, PhD
Biostatistics Research Center
Tufts-New England Medical Center #63
750 Washington Street
Boston, MA 02111
Tel (617) 636 1603 Fax (617) 636 5560
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