Before beginning a study investigating the ability of the drug heparin to prevent bronchoconstriction, baseline values of pulmonary function were measured for a sample of 12 individuals with a history of exercise-induced asthma. The mean value of forced vital capacity (FVC) for the sample is x1 = 4.49 liters and the standard deviation is s1 = 0.83 liters; the mean forced expiratory volume in 1 second (FEV 1) is x2 = 3.71 liters and the standard deviation is s2 = 0.62 liters.

(a) Compute a two-sided 95% confidence interval for Jl~o the true population mean FVC.

(b) Rather than a 95% interval, construct a 90% confidence interval for the true mean FVC. How does the length of the interval change?

(c) Compute a 95% confidence interval for JI2, the true population mean FEV1

(d) In order to construct these confidence intervals, what assumption is made about the underlying distributions of FVC and FEV 1?