A sociologist assigned to a correctional institution was interested in studying the relationship between intelligence and delinquency. A delinquency index (ranging from 0 to 50) was formulated to account for both the severity and the frequency of crimes committed, while intelligence was measured by IQ. The following table displays the delinquency index (DI) of a sample of 18 convicted minors.
a. Notice that the convicted minor with IQ = 134 and DI = 39.6 appears to be quite out of place in the data. Decide whether this outlier has any effect on your estimate of the IQ-DI relationship by looking at the graph for the fitted line obtained when the outlier is omitted. (?0 = 70.846 and ?1 = -0.444 when the outlier is removed.)
b. Test the null hypothesis of zero slope when the outlier is removed, given that Sy|x = 4.933, Sx = 14.693, and n = 17. (Use ? = .05.)
c. For these data, would you conclude that the delinquency index decreases as IQ increases?
