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st: Groups (qantiles) in Hosmer-Lemeshows goodness of fit test


From   Kaaresen Per Ivar <per.ivar.kaaresen@rito.no>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: Groups (qantiles) in Hosmer-Lemeshows goodness of fit test
Date   Wed, 12 Jun 2002 15:07:56 +0200

Ikke sensitiv - ignore message - due to in-house security

Dear friends

Could anybody help me with this (again) probably rather simple problem.

I'm working with this CRIB (clinical risk index for babies) ability to
predict hospital death in a population (not individual) level.  To test the
calibration of the score I've done a logistic regression and then a
Hosmer-Lemesow goodness of fit test. The variables are dead and crib (range
0-21, integers only).

. logit dead crib

Iteration 0:   log likelihood = -206.16559
Iteration 1:   log likelihood = -155.91351
Iteration 2:   log likelihood = -150.13801
Iteration 3:   log likelihood = -150.00793
Iteration 4:   log likelihood = -150.00765

Logit estimates                                   Number of obs   =
443
                                                  LR chi2(1)      =
112.32
                                                  Prob > chi2     =
0.0000
Log likelihood = -150.00765                       Pseudo R2       =
0.2724

----------------------------------------------------------------------------
--
        dead |      Coef.   Std. Err.      z    P>|z|     [95% Conf.
Interval]
-------------+--------------------------------------------------------------
--
        crib |   .3516896   .0414307     8.49   0.000     .2704869
.4328923
       _cons |  -4.086216   .3701967   -11.04   0.000    -4.811788
-3.360644
----------------------------------------------------------------------------
--

. lfit,group(10) table

Logistic model for dead, goodness-of-fit test
(Table collapsed on quantiles of estimated probabilities)

note: because of ties, there are only 9 distinct quantiles

_Group     _Prob     _Obs_1     _Exp_1     _Obs_0     _Exp_0     _Total
     1    0.0233          2        1.8         74       74.2         76
     3    0.0328          2        2.2         65       64.8         67
     4    0.0642          3        3.7         60       59.3         63
     5    0.0888          2        3.2         34       32.8         36
     6    0.1217          4        2.9         20       21.1         24
     7    0.2188         15       13.7         56       57.3         71
     8    0.2848         10        9.7         24       24.3         34
     9    0.4458         12       12.4         20       19.6         32
    10    0.9644         28       28.4         12       11.6         40

       number of observations =       443
             number of groups =         9
      Hosmer-Lemeshow chi2(7) =         1.34
                  Prob > chi2 =         0.9874



My question is (yes, I see the possible problem with small numbers in 5 of
the cells - but that's not the question now): How can I find the intervals
in CRIB score which the different _Group (qantiles) represent? I would like
to present the results something like:


  CRIB     _Prob     _Obs_1     _Exp_1     _Obs_0     _Exp_0     _Total
   0-1    0.0233          2        1.8         74       74.2         76
   2-4    0.0328          2        2.2         65       64.8         67
   5-7    0.0642          3        3.7         60       59.3         63
     .    0.0888          2        3.2         34       32.8         36
     .    0.1217          4        2.9         20       21.1         24
     .    0.2188         15       13.7         56       57.3         71
     .    0.2848         10        9.7         24       24.3         34
     .    0.4458         12       12.4         20       19.6         32
     .    0.9644         28       28.4         12       11.6         40


I've seen this kind of presentation in different papers - and would be very
thankful if somebody could explain how I can do this in Stata.


Regards

Per Ivar Kaaresen
MD
University Hospital Nothern Norway




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