OPTION LS=76 NOCENTER;
DATA tires;INFILE 'humidity.txt' expandtabs firstobs=2;
INPUT y time humidity;
CARDS;
PROC PRINT;
TITLE 'Print all the data';
PROC PLOT;PLOT y*time;
PROC PLOT;PLOT y*humidity;
PROC GLM;MODEL y=time humidity;
TITLE 'For model y=time humidity';
OUTPUT OUT=new P=yhat RESIDUAL=res1 PRESS=press1;  

PROC PRINT DATA=new;VAR y YHAT res1 press1;

PROC MEANS MEAN VAR USS DATA=NEW;VAR res1 press1;
TITLE 'Note the huge difference between full model error and PRESS error';
PROC PLOT DATA=new;PLOT res1*y;

/* To consider humidity as discrete */

DATA humclass;SET tires; 
PROC GLM;CLASS humidity;
MODEL y=time humidity;
RUN;