/*  This SAS code computes sample sizes needed 
    to obtain equivalence tests for comparing
    two success rate with specified power values. 
    
    This code is posted in the file power2e.sas   */

proc iml;
  start equiv;
  p1 = .7;             * Enter success probability p1;
                       * for the standard treatment;

  rrb = 1.2;           * Enter upper bound on relative;
                       * risk to maintian equivalence ;
                       * Upper bound for p2/p1 ;

  power = {.8 .9};     * Enter a set of power values;

  rra = {1.05 1.10};   * Enter relative risk for some alternatives; 

  alpha = .05;         * Enter the type I error level;

  nb = ncol(power);
  np = ncol(rra);
  size = j(1,np);
  

  do i1 = 1 to np;              * Cycle across alternatives;
     rr = rra[1,i1];
	 pa = probit(1-alpha)*sqrt(1+1/rr);

  do i2 = 1 to np;              *  Cycle across power levels;
     pb=probit(power[1,i2])*sqrt(1+1/rrb);
     size[1,i2] = ((pb+pa)/log(rrb/rr))**2;
  end;

  print,,,,,,, p1 RR alpha power;
  size = int(size) + j(1,np);
  print 'Sample size for each treatment:' size;
  end;
finish;

run equiv;