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st: prvalue after zinb


From   "Li, Wenjun" <WLi1@tufts-nemc.org>
To   "Statalist (E-mail)" <statalist@hsphsun2.harvard.edu>
Subject   st: prvalue after zinb
Date   Thu, 17 Apr 2003 14:14:54 -0400

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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