options pageno=min nodate formdlim='-'; title 'Matching and ANCOV with Confounded Covariate'; run; data confound; input gender courses aptitude pair apt1 apt2 diff; interaction = gender*courses; cards; 1 12 66 . . . . 1 10 64 . . . . 1 9 57 . . . . 1 9 53 . . . . 1 8 53 . . . . 1 8 50 . . . . 1 8 47 . . . . 1 7 43 1 . . . 2 7 52 1 . . . . . . 1 43 52 9 1 7 47 2 . . . 2 7 48 2 . . . . . . 2 47 48 1 1 6 43 3 . . . 2 6 48 3 . . . . . . 3 43 48 5 1 6 40 4 . . . 2 6 45 4 . . . . . . 4 40 45 5 1 6 37 5 . . . 2 6 42 5 . . . . . . 5 37 42 5 1 5 33 6 . . . 2 5 38 6 . . . . . . 6 33 38 5 1 5 35 7 . . . 2 5 40 7 . . . . . . 7 35 40 5 1 5 37 8 . . . 2 5 42 8 . . . . . . 8 37 42 5 1 4 32 9 . . . 2 4 33 9 . . . . . . 9 32 33 1 1 4 28 10 . . . 2 4 37 10 . . . . . . 10 28 37 9 2 3 34 . . . . 2 3 26 . . . . 2 2 21 . . . . 2 2 29 . . . . 2 1 23 . . . . 2 1 17 . . . . 2 0 15 . . . . proc corr; var gender courses aptitude; proc ttest; class gender; var courses aptitude; proc means mean stddev n t prt; var apt1 apt2 diff; proc glm; class gender; model aptitude = courses gender interaction / ss1; title 'Test the interaction term'; run; proc glm; class gender; model aptitude = courses gender / ss1; means gender; lsmeans gender; title 'ANCOV with effect of gender adjusted for number of courses'; run;