Littell et al. (2000) described a pharmaceutical clinical trial in which 24 patients were randomly assigned to each of three treatment groups (drug A, drug B, placebo) and compared on a measure of respiratory ability (FEV1 =

forced expiratory volume in 1 second, in liters). The data file8FEV.dat at www.stat.ufl.edu/~aa/glm/data has the form shown in Table 1.4.

Here, we let y be the response after 1 hour of treatment (variable fev1 in the data file), x1 = the baseline measurement prior to administering the drug (variable base in the data file), and x2 = drug (qualitative with labels

a,

b, p in the data file). Download the data and fit the linear model for y with explanatory variables

(a) x1,

(b) x2,

(c) both x1 and x2. Interpret model parameter estimates in each case.

Table 1.4 Part of FEV Clinical Trial Data File for Exercise 1.21 Patient Base fev1 fev2 fev3 fev4 fev5 fev6 fev7 fev8 Drug 01 2.46 2.68 2.76 2.50 2.30 2.14 2.40 2.33 2.20 a 02 3.50 3.95 3.65 2.93 2.53 3.04 3.37 3.14 2.62 a 03 1.96 2.28 2.34 2.29 2.43 2.06 2.18 2.28 2.29 a

...

72 2.88 3.04 3.00 3.24 3.37 2.69 2.89 2.89 2.76 p Complete data (file FEV.dat) are at the text website www.stat.ufl.edu/~aa/glm/data