Chapter 9
Multicollinearity
9.1 a. The correlation between x1 and x2 is .824.
b. The variance inflation factors are 3.1.
c. The condition number of X′X is κ = 40.68 which indicates that multicollinearity is not a problem in these data.
9.3 The eigenvector associated with the smallest eigenvalue is
| Eigenvector |
| −0.839 |
| 0.081 |
| 0.437 |
| 0.117 |
| 0.289 |
All four factors contribute to multicollinearity.
9.5 There are two large condition indices in the non-centered data. In general, it is better to center.

9.7 a. The correlation matrix is

which indicates that there is a potential problem with multicollinearity.
b. The variance inflation factors are
| Regressor |
VIF |
| x1 |
117.6 |
| x2 |
33.9 |
| x3 |
116.0 |
| x6 |
4.6 |
| x7 |
5.4 |
| x8 |
18.2 |
| x9 |
7.6 |
| x10 |
78.6 |
| x11 |
5.1 |
which indicates there is evidence of multicollinearity.
9.9 The condition indices are
| 1.00
9.65
61.93
126.11
2015.02
5453.08
44836.79
85564.32
5899200.59
8.86 × 1012 |
which indicate a serious problem with multicollinearity.
9.11 The condition number is κ = 24,031.36 which indicates a problem with multicollinearity. The variance inflation factors shown below indicate evidence of multicollinearity.
| Regressor |
VIF |
| x1 |
3.67 |
| x2 |
7.73 |
| x3 |
19.20 |
| x4 |
7.46 |
| x5 |
4.69 |
| x6 |
7.73 |
| x7 |
1.12 |
9.13 The condition number is κ = 12400885.78 ...