The SAS System                                1
                                               15:50 Thursday, November 20, 2003

               Plot of X1*X2.  Legend: A = 1 obs, B = 2 obs, etc.

X1 |
   |
12 +
   |
   |
   |                                                       A
11 +
   |
   |
   |
10 +
   |
   |
   |
 9 +
   |                               A                         A     A
   |
   |
 8 +
   |                                            A  A
   |                                        A             A
   |                                                 A
 7 +
   |               A                   A        A
   |                           A           A  A          A  A      A
   |                                          A                   A
 6 +                                                A              A
   |                         A     A           A    A   A  A     A         A
   |                                    A   AA
   |                                  AAB A
 5 +                                          B     A
   |                                           A                   A
   |                                                     A
   | A
 4 +                                                            A
   |                                   A             A     A
   |                 A                                      A    A
   |                                              A
 3 +
   |
   |                                                      A
   |
 2 +
   |
   --+-------+-------+-------+-------+-------+-------+-------+-------+-------+--
     8      18      28      38      48      58      68      78      88      98

                                         X2

                                                                                
                                 The SAS System                                2
                                               15:50 Thursday, November 20, 2003

               Plot of X1*X3.  Legend: A = 1 obs, B = 2 obs, etc.

     X1 |
        |
     12 +
        |
        |
        |                                            A
     11 +
        |
        |
        |
     10 +
        |
        |
        |
      9 +
        |    A                            A         A
        |
        |
      8 +
        |                              A                            A
        |                               A        A
        |                                  A
      7 +
        |                A              A       A
        |              AA  A                 A   AA
        |                                        A         A
      6 +       A                                      A
        |                         A  A    AA       AA  A           A
        |                                A         AA
        |                        A        A  A     A      A
      5 +                              A   A A
        |                                    A              A
        |                                                      A
        |                                                             A
      4 +                                                    A
        |               A                       A      A
        |                      A                       A  A
        |                             A
      3 +
        |
        |                                          A
        |
      2 +
        |
        ---+-----------+-----------+-----------+-----------+-----------+--
          20          40          60          80          100         120

                                        X3

                                                                                
                                 The SAS System                                3
                                               15:50 Thursday, November 20, 2003

               Plot of X1*X4.  Legend: A = 1 obs, B = 2 obs, etc.

X1 |
   |
12 +
   |
   |
   |                                                          A
11 +
   |
   |
   |
10 +
   |
   |
   |
 9 +
   |                           A      A                               A
   |
   |
 8 +
   |                                    A        A
   |                        A A
   |                                      A
 7 +
   |                     A A    A
   |              A       B  A     AA
   |                                A          A
 6 +                           A    A
   |                A    A      A      AAA    B
   |                    A       A   A
   |                    A      AAA A
 5 +                   A           A     A
   |                           A               A
   |                                 A
   |                               A
 4 +                                                A
   |                  A       A A
   |             A A A
   |         A
 3 +
   |
   |                       A
   |
 2 +
   |
   ---+---------+---------+---------+---------+---------+---------+---------+--
      0         1         2         3         4         5         6         7

                                        X4