***********************************************************************
* This is a program that illustrates the use of PROC LOGISTIC in SAS  *
* to perform ordinal logistic regression.                             *
*                                                                     *
* The sample data set is taken from the following article:            *
*    Boyle RM, Chinchilli VM, Shasky DA.  (1993).  Masking of         *
*    Physicians in the Growth Failure in Children with Renal Diseases *
*    Clinical Trial.  Pediatric Nephrology 7, 204-206.                *   
***********************************************************************;

proc format;
value scorefmt -3='Incorrect_certain'
               -2='Incorrect_probable'
               -1='Incorrect_guess'
                0='Unsure'
                1='Correct_guess'
                2='Correct_probable'
                3='Correct_certain';
run;

data gfrd;
input center id months score trtgroup $;
format score scorefmt.;
label months='Months on Study';
cards;
   1       1906        9         2       A  
   2       2901        9         1       B  
   3       3908       56        -1       B  
   3       3911       15         1       A  
   3       3919        9         1       B  
   4       4901       25         1       A  
   4       4912       12         1       B  
   4       4913       13         1       B  
   5       5901        0         0       A  
   5       5902       28         0       A  
   5       5905        2         0       B  
   6       6904       13        -2       A  
   6       6920       11        -2       A  
   6       6922       10         2       A  
   7       7905       29        -1       B  
   7       7910       39         1       A  
   7       7916       40         1       A  
   7       7919       23         1       A  
   7       7920        4        -1       B  
   7       7921       26        -1       B  
   7       7926       33         1       A  
   7       7927       30         1       A  
   7       7929       14        -1       B  
   7       7930       17        -1       B  
   7       7931       12         1       A  
   8       8904       18        -1       B  
   8       8905       30        -1       A  
   8       8909        9         1       B  
   8       8915        2         1       A  
   8       8917        5        -1       B  
   8       8918        2        -1       A  
   9       9901       45        -1       B  
   9       9903       54         1       A  
   9       9907       61         1       B  
   9       9908       28        -1       B  
   9       9918       31         1       A  
   9       9919       25         1       A  
  11      11901       21        -1       B  
  11      11905       47        -2       B  
  11      11906       15        -1       A  
  14      14902       14        -1       B  
  14      14907        0         1       B  
  14      14908       38        -1       A  
  14      14911        0         0       A  
  14      14912       36         1       B  
  14      14913       32        -1       A  
  14      14916        1         1       A  
  14      14917        7         1       A  
  16      16904       31         1       A  
  16      16905       34         1       A  
  16      16906       13        -1       B  
  18      18902       11         1       B  
  18      18904        8         1       B  
  21      21906       46         2       B  
  21      21910       14        -2       B  
  21      21912        6         2       A  
  21      21915       26        -2       A  
  21      21916       25         2       B  
  21      21917       26        -2       A  
  21      21918       26        -2       B  
  21      21919       19         2       A  
  21      21920       15        -2       A  
  21      21921        2        -2       B  
  21      21922       15         2       B  
  22      22901       26         1       A  
  22      22902       26         1       B  
  22      22903       26         1       A  
  22      22909        5         1       B  
  23      23901       31        -1       B  
  23      23903        7         1       B  
  24      24914        9         2       B  
  24      24917       22        -2       A  
  24      24918        6         1       A  
  24      24919        2        -2       B  
  26      26901        6        -2       B  
  26      26903        7        -2       A  
  27      27901       15        -1       A  
  27      27904       18         1       B  
  27      27905        3        -2       B  
  28      28901        7         2       A  
  28      28902       33         1       B  
  28      28904        4         1       A  
  28      28905       16        -2       B  
  30      30912       15         2       A  
  31      31901        1         1       A  
  31      31902       38         1       B  
  31      31903       31        -1       B  
  35      35901        6         0       A  
  35      35904       11         0       B  
  38      38907        4         0       A  
  41      41904        9         2       B  
  42      42901        2         1       A  
  42      42903        2        -1       B  
  42      42904        2        -1       B
;
run;

proc print data=gfrd;
title 'GFRD Example';
run;

data gfrd2;
set gfrd;
newscore=0;
if score>0 then newscore=1;
treatment=0;
if trtgroup="A" then treatment=1;
run;

proc logistic data=gfrd2 order=internal descending;
model newscore=treatment months;
title2 'Logistic Regression of the Masking Score';
run;