proc glm data=ma2612.asphalt plots (only)=none;
 class site type;
 model wear=type site;
 output out=asphalt_out p=predicted;
run;
quit;

* The next bit of code constructs the Tukey 1 df for nonadditivity test
*
*Get mean of wear from output: it equals 53.0
*Rescale the predicted values;
title 'Tukey Test for Interaction';
data asphalt_out1;
  set asphalt_out;
  rescale=predicted**2/(2*53);
run;
proc glm data=asphalt_out1;
 class site type;
 model wear=site type rescale;
 contrast 'Tukey eta' rescale 1;
 ods select contrasts;
run;
quit;
/* The interaction term is not significant, so we can analyze
the fit of the additive model.*/
title 'Interaction Plot 1';
proc glm data=ma2612.asphalt;
 class site type;
 model wear=site type site*type;
 ods select intplot;
run;
quit;
title 'Interaction Plot 2';
proc glm data=ma2612.asphalt;
 class type site;
 model wear=type site type*site;
 ods select intplot;
run;
quit;
title ' ';