7.42 data 4.7 on page 323 introduces a study investigating the effectiveness of two drugs, desipramine and lithium, in the treatment of cocaine addiction. the subjects in the six-week study were cocaine addicts seeking treatment. the 72 subjects were randomly assigned to one of three groups (desipramine, lithium, or a placebo, with 24 subjects in each group) and the study was double-blind. in example 4.34 we test lithium vs placebo, and in exercise 4.181 we test desipramine vs placebo. now we are able to consider all three groups together and test whether relapse rate differs by drug. ten of the subjects taking desipramine relapsed, 18 of those taking lithium relapsed, and 20 of those taking the placebo relapsed. create a two-way table of the data. find the expected counts. is it appropriate to analyze the data with a chi-square test? if it is appropriate to use a chi-square test, complete the test. include hypotheses, and give the chi-square statistic, the p-value, and an informative conclusion. if the results are significant, which drug is most effective? can we conclude that the choice of treatment drug causes a change in the likelihood of a relapse?