In a trial, 2500 people were given a flu vaccine and a separate 2500 people were given a placebo (a dummy injection). During the flu season, 25 of the vaccinated people caught flu, compared with 100 of the people who had the placebo.
(a)Work out the risk of catching flu for someone who had the vaccine. Give your answer as a percentage.(2)
(b)Work out the risk of catching flu for someone who had the placebo. Give your answer as a percentage.(2)
(c)Work out the relative risk: how many times as likely is a person who had the placebo to catch flu compared with a person who had the vaccine?(2)
(d)A health website states, "This vaccine cuts your personal risk of catching flu by three-quarters." Use your answers to explain whether this is a fair and accurate way to describe the results.(2)
(e)The vaccine is offered to two clinics: Clinic 1 has 12000 registered patients and Clinic 2 has 3000 registered patients. Assuming nobody at either clinic is vaccinated, use the placebo risk from part b to estimate how many more people would be expected to catch flu at Clinic 1 than at Clinic 2.(3)
(Total for Question 16 is 11 marks)