The variance of the quantity p hat sub 2 i minus p hat sub 1 i is equal to cap D sub i times the sum of two quantities. The first quantity is the product of 1 over n sub 1 i times p hat sub 1 i times the difference 1 minus p hat sub 1 i. The second quantity is the product of 1 over n sub 2 i times p hat sub 2 i times the difference 1 minus p hat sub 2 i. The variable i can take on the values 1 and 2.