/* hald2.sas */
options ls=72 ps=60;
data hald;
   input y x1 x2 x3 x4;
cards;
78.5 7 26 6 60
74.3 1 29 15 52
104.3 11 56 8 20
87.6 11 31 8 47
95.9 7 52 6 33
109.2 11 55 9 22
102.7 3 71 17 6
72.5 1 31 22 44
93.1 2 54 18 22
115.9 21 47 4 26
83.8 1 40 23 34
113.3 11 66 9 12
109.4 10 68 8 12
;
proc reg data=hald;
   model y = x1-x4 / selection=forward slentry=.10 details;
   model y = x1-x4 / selection=backward slstay=.10 details;
   model y = x1-x4 / selection=stepwise slentry=.10 slstay=.10 details;
title 'sequential selection methods';
proc reg data=hald;
   model y = x1 / ss1 ss2;
   model y = x2 / ss1 ss2;
   model y = x3 / ss1 ss2;
   model y = x4 / ss1 ss2;
   model y = x4 x1 / ss1 ss2;
   model y = x4 x2 / ss1 ss2;
   model y = x4 x3 / ss1 ss2;
   model y = x4 x1 x2 / ss1 ss2;
   model y = x4 x1 x3 / ss1 ss2;
   model y = x4 x1 x2 x3 / ss1 ss2;
title 'regressions for forward selection';
proc reg data=hald;
   model y = x1 x2 x3 x4 / ss1 ss2;
   model y = x1 x2 x4 / ss1 ss2;
   model y = x1 x2 / ss1 ss2;
title 'regressions for backward selection';
proc reg data=hald;
   model y = x1 x4 / ss1 ss2;
   model y = x1 x4 x3 / ss1 ss2;
   model y = x1 x2 x3 / ss1 ss2;
title 'regressions for stepwise selection';
run;