Another aspect of the preceding study involves looking at the effect of smoking on baseline pulmonary function and on change in pulmonary function over time. We must be careful since FEV depends on many factors, particularly age and height. Suppose we have a comparable group of 15 men in the same age and height group who are smokers and we measure their FEV at year 0. The data are given (For purposes of this exercise assume equal variance where appropriate).

FEV FEV FEV FEV Year 0 Year 2 Year 0 Year 2 Person (L) (L) Person (L) (L) 1 2.85 2.88 9 2.76 3.02 2 3.32 3.40 10 3.00 3.08 3 3.01 3.02 11 3.26 3.00 4 2.95 2.84 12 2.84 3.40 5 2.78 2.75 13 2.50 2.59 6 2.86 3.20 14 3.59 3.29 7 2.78 2.96 15 3.30 3.32 8 2.90 2.74

a. Graphically display the distribution of change in pulmonary function for smokers and nonsmokers (from the previous problem)

b. Calculate a confidence interval to determine if there is evidence to suggest that the change in pulmonary function over 2 years is the same in the two groups. State your assumptions and interpret your results