A manufacturer wanted to know if more coupons would be redeemed if they were mailed to the female in the household rather than the male in the household. A coupon book was sent at random to either the male or female in a random sample of 50 male-female households. A month later, a coupon book was sent to the other member of the pair. The manufacturer found that the mean difference (female - male) in the number of coupons redeemed was 1.5 with a standard deviation of 4.75.