=+samples of size n1 and n2, respectively, are independently selected from the two populations, and let p1 and p2 denote the resulting sample proportions of successes. If the sample sizes are sufficiently large

(apply the rule of thumb appropriate for a single proportion to each sample separately), the statistic p1 2 p2 has approximately a normal sampling distribution with mean value 1 2 2 and standard deviation 11(1 2 1)yn1 1 2(1 2 2)yn2. The