A major clinical trial of a new vaccine for type-B hepatitis was conducted with a high-risk group of 1083 male volunteers. From this group, 549 men were given the vaccine and the other 534 a placebo. A follow-up of all these individuals yielded the data:

(a) Do these observations testify that the vaccine is effective? Use α = .01.
(b) Construct a 95% confidence interval for the difference between the incidence rates of hepatitis among the vaccinated and non vaccinated individuals in the high-risk group.

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Follow-up Did Not Got Hepatitis Get Hepatitis Total Vaccine Placebo 538 464 549 534 70