A study of chromosome abnormalities and criminality examined data from 4,124 males born in Copenhagen. Each man was classified as having a criminal record or not, using the registers maintained in the local police offices. Each was also classified as having the normal male XY chromosome pair or one of the abnormalities XYY or XXY. Of the 4,096 men with normal chromosomes 381 had criminal records, while 8 of the 28 men with normal chromosomes had criminal records. Some experts believe chromosome abnormalities are associated with increased criminality.
(a) Do these data lend support to this belief? Perform a significance test to answer this question.
(b) Construct and interpret a 95% confidence interval for the difference in proportions.