option nocenter ps=65 ls=75;

data lambs;
 input diet wtgain @@;
 cards;
  1  8  1 16  1  9
  2  9  2 16  2 21
  2 11  2 18  3 15
  3 10  3 17  3  6
;

/* Generate side by side boxplots */
symbol1 bwidth=5 i=box; axis1 offset=(5);
proc gplot; plot wtgain*diet / frame haxis=axis1;

/* Use GLM instead of REG */
proc glm; 
 class diet;
 model wtgain=diet;
 output out=diag r=res p=pred;

/* Generate a residual boxplots */
proc gplot; plot res*diet /frame haxis=axis1;

/* Generate residual plot and horizontal line at zero */
proc sort; by pred;
symbol1 v=circle i=sm50;
proc gplot; plot res*pred / haxis=axis1;
run;
quit;