(Using Duncan’s regression of occupational prestige on the educational and income levels of occupations, verify that the influence vector for the deletion of ministers on the regression coefficients, di ¼ b $ bð$iÞ, can be written as di ¼ ðX0 XÞ

$1 xi Ei 1 $ hi where xi is the ith row of the model matrix X (i.e., the row for ministers) written as a column.

[A much more difficult problem is to show that this formula works in general; see, e.g., Belsley, et al. (1980, pp. 69–83) or Velleman and Welsch (1981).]