options ls = 80 ps = 56 ; data task2 ; length pie $ 9 ; input pie $ hours taste ; cards ; custard 4.1 5.5 custard 3.2 4.9 custard 2.3 4.6 custard 3.0 5.1 custard 2.9 4.8 custard 3.0 4.8 custard 4.1 5.3 custard 2.1 4.6 custard 2.5 4.6 custard 4.2 5.5 custard 3.1 5.0 custard 4.2 5.6 mincemeat 3.7 5.6 mincemeat 4.5 6.2 mincemeat 4.2 6.2 mincemeat 5.4 7.4 mincemeat 4.4 6.4 mincemeat 3.5 5.7 mincemeat 5.0 6.8 mincemeat 4.9 6.7 mincemeat 3.0 5.1 mincemeat 3.8 5.9 mincemeat 3.3 5.2 mincemeat 3.0 5.1 pumpkin 5.9 6.4 pumpkin 4.3 5.8 pumpkin 4.7 5.6 pumpkin 6.3 6.5 pumpkin 6.4 6.7 pumpkin 5.1 5.9 pumpkin 5.6 6.3 pumpkin 5.2 5.8 pumpkin 4.3 5.6 pumpkin 4.0 5.3 pumpkin 4.4 5.6 pumpkin 4.1 5.7 ; proc print ; run ; proc univariate ; var hours ; * test for unequal slopes (interaction between the treatment and covariate) ; proc glm ; class pie ; model taste = pie hours hours*pie / solution ; run ; * Investigate the interaction by comparing groups at several x values. Here we use the three quartiles of the x distribution ; proc glm ; class pie ; model taste = pie hours hours*pie / solution ; estimate 'pumpkin at 3.2 hours' intercept 1 pie 0 0 1 hours 3.2 hours*pie 0 0 3.2 ; estimate 'custard at 3.2 hours' intercept 1 pie 1 0 0 hours 3.2 hours*pie 3.2 0 0 ; estimate 'mincemeat at 3.2 hours' intercept 1 pie 0 1 0 hours 3.2 hours*pie 0 3.2 0 ; lsmeans pie / at hours = 3.2 pdiff adjust = tukey ; lsmeans pie / at hours = 4.2 pdiff adjust = tukey ; lsmeans pie / at hours = 4.8 pdiff adjust = tukey ; run ; proc plot ; plot taste*hours=pie ; run ;