title 'Estimates and Confidence Intervals for Differences of Means';
proc glm data=ma2612.feedback plots=none;
 class feedback;
 model add_value=feedback;
 means feedback/cldiff lsd alpha=.05;
 ods select CLDiffs;
run;
title 'Estimates, Standard Errors and Hypothesis Tests for Differences of Means';
proc glm data=ma2612.feedback plots=none;
 class feedback;
 model add_value=feedback;
 estimate 'Accurate-None' feedback 1 -1 0;
 estimate 'Accurate-Vague' feedback 1 0 -1; 
 estimate 'Vague-None' feedback 0 -1 1;
 ods select estimates;
run;quit;
title ' ';