The real data set in this question first appeared in Hald XXXXXXXXXXThe data are given in Table 7.5 and can be found on the book web site in the file Haldcement. txt. Interest centers on using...

The real data set in this question first appeared in Hald (1952). The data are given in Table 7.5 and can be found on the book web site in the file Haldcement. txt. Interest centers on using variable selection to choose a subset of the predic-tors to model Y. Throughout this question we shall assume that the full model below is a valid model for the data
Y = /30 + + /32X2 + /33 X3 + /34X4 + e (7.9) Output from R associated with different variable selection procedures based on model (7.9) appears on the following pages:
6 7 Variable Selection
Table 7.5 Hald's real data Y xi x2 x3 78.5 7 26 6 60 74.3 I 29 15 52 104.3 11 56 8 20 87.6 11 31 8 47 95.9 7 52 6 33 109.2 11 55 9 22 102.7 3 71 17 6 72.5 I 31 22 44 93.1 2 54 18 22 115.9 21 47 4 26 83.8 1 40 23 34 113.3 11 66 9 12 109.4 10 68 8 12