data zinc;
  infile 'c:/philip/stat505/zinc.txt' firstobs=2;
  input zinc cens $;

  if cens = 'TRUE' then do;
     lower = .;				/* or 0 */
	 upper = zinc;
	 end;
   else do;
     lower = zinc;
	 upper = zinc;
	 end;

/* mle */
 proc lifereg;
   model (lower,upper) =  /d=normal;
   run;