.-
help for ^lrchg^
.-

Calculates change in coefficients between logistic models 
----------------------------

    ^lrchg^ , store(n)
	or
    ^lrchg^ , contr(n m)


Description
-----------

^lrchg^ displays the coefficients in two logistic models, and
calculates the proportion of change in coefficients between two
models.

This is useful in logistic regression modelling in epidemiology.

Use 
    ^lrchg^ , store(1) 
    ^lrchg^ , store(2) 
    ^lrchg^ , contr(1 2) 

to store two models, then contrast them.

Options
-------

store(n)
   Stores logistic regression results in a variable coeffn
   Use before contrasting two models.

contr(n m)
   Contrasts two models previously stored.         

nocoeff
   Drop the calculations of changes in coefficients.
   
Examples
--------

. xi: logistic response i.agek6 i.gend i.agek6*i.gend i.regio 
. lrchg, store(0)
. xi: logistic response i.agek6 i.gend i.agek6*i.gend
. lrchg, store(1)
. lrchg, contr(0 1)

Likelihood ratio tests and change in coefficients
between logistic regression models
--------------------------------------------------
Diff. in LL =           99.855
Diff. in df  =               1
P-value      =          0.0000

Change in common coefficients 
between models 0 and 1:

 Coefficient   Model 0      Model 1   %change
--------------------------------------------------
 Iage_1         0.9293       0.8923       4.0
 Iage_2         1.2648       1.2064       4.6
 Igend_2        1.6332       1.6133       1.2
 IaXg_1_2       0.9801       0.9834      -0.3
 IaXg_2_2       0.9768       0.9848      -0.8
--------------------------------------------------
 Iregio_2       0.9293       0.0000      uniq

Remarks 
-------
Presently the coefficients are stored in matrices named
coeff`n'. This shouldn't cause any problems, but it is
not elegant.

It might be better to use -estimates hold-  but will 
have to get back to this.

The author wonders what to do if there are zero degrees 
of freedom ?

Inspired by the program lrdrop1 by Zhiqiang Wang.

Author
-------
    Jan Brogger, University of Bergen, Norway
    jan.brogger@@med.uib.no (21 May 2000)

Shameless plug :)
--------------
 I am looking for internship & residency  in internal 
 medicine/pulmonary medicine US/EU. Am doing PhD in respiratory 
 epidemiology now. 
