options formdlim =  '-';

data camp;
  infile 'camp.txt' firstobs = 2;
  input group hr0 hr4;
  diff =  hr4-hr0;
    
proc plot;
  plot hr4*hr0 = group;
run;
     
proc glm;
  class group;
  model diff hr0 hr4 = group;
  lsmeans group /stderr;
  title 'Difference, Pre only and Post only';
  
proc glm;
  class group;
  model hr4 = group hr0 /solution;
  lsmeans group /stderr;
  lsmeans group /stderr at hr0 = 5;
  
  estimate 'slope' hr0 1;
  
  estimate 'group 2 - 1' group -1 1 0 0;
  
  title 'ANCOVA, equal slopes';
  
proc glm;
  class group;
  model hr4 = group hr0 hr0*group;
  lsmeans group /stderr at hr0 = 5;
  lsmeans group /stderr at hr0 = 10;
  lsmeans group /stderr at hr0 = 15;
  
  title 'ANCOVA, diff slopes';
  
run;