Question: The National Health Interview Survey conducted 33,326 adults by the U.S. National Center for Health Statistics in 2003 indicated that 21.4% of adults were current smokers. A similar study conducted in in 1991 of 42,000 adults indicated that 25.6% were current smoker.

a. Find the interpret a point estimate of the difference between the proportion of current smokers in 1991 and the proportion of current smokers in 2003.

b. A 99% confidence interval for the true difference is (0.034, 0.050). Interpret

c. What assumptions must you make for the interval in (b) to be valid?