The hii are often used to denote leverage—that is, a point that is unusual in its location in the x-space and that may be influential. Generally, the ith point is called a leverage point if hii exceeds 2pn, which is twice the average size of all the hat diagonals. Recall that p  k  1.

(a) Table 6-8 contains the hat matrix diagonal for the wire bond pull strength data used in Example 6-7. Find the average size of these elements.

(b) Based on the criterion given, are there any observations that are leverage points in the data set?