MACRO

CompProp nreps n1 n2 phat obsdiff

Mconstant nreps n1 n2 phat obsdiff Count Pvalue I
Mcolumn x1 phat1 x2 phat2 diff x

Random nreps x1;
  Binomial n1 phat.
Let phat1 = x1 / n1
Random nreps x2;
  Binomial n2 phat.
Let phat2 = x2 / n2
Let diff = phat1-phat2
Sort diff diff;
  By diff.

Let Count = 0

DO I = 1:nreps
IF abs(diff(I)) GE obsdiff
Let Count = Count +1
ENDIF
ENDDO

Let Pvalue=Count/nreps

Print Pvalue

Stem-and-Leaf diff.

Histogram diff;
  Percent;
  CutPoint -1:1/.1;
  Bar;
    Type 1;
    Color 3;
  Title "Resampling Distribution";
  Title "Difference in 2 proportions";
  Minimum 1 -1;
  Maximum 1 1;
  ScFrame;
  ScAnnotation;
  Axis 1;
    Label "Difference in Proportions";
  Axis 2;
  Tick 1;
    NMajor 5;
    NMinor 4;
  Tick 2;
    NMajor 6;
    NMinor 4.

ENDMACRO