/*
Comparing two proportions using pooled standard errors.
www.estat.us

*/
data homework;
/*percent from group A*/
measure1=.07;
/*percent from group B*/
measure2=.1;

/*Ns for the two groups*/
n1=500;
n2=500;

/*standard errors for group A*/
x1=(measure1*(1-measure1));
Error1=sqrt(x1/(n1) );

/*standard errors for group B*/
x2=(measure2*(1-measure2));
Error2=sqrt(x2/(n2) );

/*getting T-statistic by deviding a) difference in probability by b) pooled standard errors */
DIFZ= (measure1 - measure2)/sqrt(error1**2+error2**2);

/*evaluating the T-statisic by Z-distribution*/
DIFProb=probnorm(DIFZ);

/*Give a * if the difference in the probabilities is statistically siginificant
at 5% level*/
if DIFPROB < .05 and DIFPROB ne . then DIFtest="*";

run;

proc print;
run;