11.17 Cognitive behavioral therapy and anxiety A study used 1496 patients suffering from low levels of anxiety. The study randomly assigned each subject to a cognitive behavioral therapy (CBT) treatment or a placebo treatment. In this study, increased anxiety levels were observed for 45 of the 729 subjects taking a placebo and for 29 of the 767 subjects taking CBT.

a. Report the data in the form of a 2 * 2 contingency table.

b. Show how to carry out all five steps of the null hypothesis that having an anxiety attack is not associated with whether one is taking a placebo or CBT. (You should get a chi-squared statistic equal to 4.5.) Interpret.