A National Center for Health Statistics data brief published in 2015 (Nr. 181) looked at the association between lung obstruction and smoking status in adults 40 to 79 years old. In a random sample of 6927 adults without any lung obstruction, 54.1% never smoked. In a random sample of 1146 adults with
lung obstruction (such as asthma or COPD), 23.8% never smoked.
a. Find and interpret a point estimate of the difference between the proportion of adults without and with lung obstruction who never smoked.
b. A 99% confidence interval for the true difference is (0.267, 0.339). Interpret.
c. What assumptions must you make for the interval in part b to be valid?