/* Example of using DO WHILE and DO UNTIL statements in SAS */
 
/* Program to determine the sample size needed for a sample mean of 0.1 to be judged      */
/* significantly greater than zero at the 0.05 significance level by a t-test (when s=2). */

DATA results;
sampmean = 0.1;
sampsd = 2;
sampsize = 10;
tstat = sampmean / (sampsd / sqrt(sampsize) );
tcritval = tinv(0.95, sampsize-1);

DO WHILE (tstat LE tcritval);
tstat = sampmean / (sampsd / sqrt(sampsize) );
tcritval = tinv(0.95, sampsize-1);
OUTPUT;
sampsize = sampsize + 10;
* sampsize + + 10;
END;

run;

PROC PRINT DATA = results;
RUN;

/* Almost the same thing, but using DO UNTIL construction: */

DATA results;
sampmean = 0.1;
sampsd = 2;
sampsize = 10;
tstat = sampmean / (sampsd / sqrt(sampsize) );
tcritval = tinv(0.95, sampsize-1);

DO UNTIL (tstat GT tcritval);
tstat = sampmean / (sampsd / sqrt(sampsize) );
tcritval = tinv(0.95, sampsize-1);
OUTPUT;
sampsize = sampsize + 10;
END;

run;

PROC PRINT DATA = results;
RUN;



/* Change sampsd to .002 in both cases and see the difference */
/* between DO WHILE and DO UNTIL in that situation.           */