12. Refer to the variables in Table 9.16 Perhaps surprisingly, a moderate positive correla- tion exists between crime rate and percent who are at least high school graduates (r = .468). Percentage living in metropolitan areas is also strongly positively correlated both with come rate (r = .678) and with high school graduation rate (r = .791).

a) Explain why the association between crime rate and high school graduation rate could disappear, or even change direction, when we control for percentage living in metropoli- lan areas,

b) Which type of relationship is more plausible for these variables. a spurious relationship or a chain relationship? Explain.