Eighty-six patients with bladder cancer participated in a study in which all tumors were removed and then the subjects were monitored to see if the tumors returned. Patients were randomly assigned to one of two treatment groups: one group received a placebo, and one group received the drug thiotepa. Tumors returned in 29 out of 48 patients in the placebo group and in 18 out of 38 patients in the thiotepa group. (6 points) a) Find and interpret a 90% confidence interval for the difference in the proportion of tumors returning between the two treatments. b) Using the confidence interval, is it plausible that the drug appears to be more effective than the placebo in preventing tumor regrowth? Explain why or why not?

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