Yesterday it was announced that the first-ever cold vaccine to be tested in a la

Question

Yesterday it was announced that the first-ever cold vaccine to be tested in a large number of people has failed, over all, to protect them from infection with the virus that causes the disease, according to the company that makes the vaccine, ColdVax. People in the trial were either injected with the vaccine or with a placebo. Among the results published in the New York Times were the following summary of the numbers of people at the end of the three-year trial: What was the probability that a person in the trial was given the vaccine instead of the placebo? a) 191/3, 330 b) 3, 139/3, 330 c) 3, 191/5,009 d) 3, 330/5,009 Of the people given the vaccine, what was the probability they were not infected with a cold at the end of the three-year trial? a) 191/3, 330 b) 3, 139/3, 330 c) 3, 191/5,009 d) 3, 330/5,009 Of the people given the placebo, what was the probability they were not infected with a cold at the end of the three-year trial? a) 1, 581/1, 679 b) 1, 679/4, 720 c) 4, 720/5,009 d) 1, 679/5,009

Explanation / Answer

Answer 9

3330 / 5009.

Answer 10

P (not infected | vaccine) = P (not infected and vaccine) / P (vaccine) = 3139 / 3330.

Answer 11

P (not infected | placebo) = P (not infected and placebo) / P (placebo) = 1581 / 1679.

Thanks.

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