Jonas Salk's polio vaccine trials of 1954 involved giving placebos to 201,229 children and the polio vaccine to 200,745 children. Out of those in the placebo group, 142 children developed polio, whereas 57 children from the vaccine group developed polio. Approximately how many less times likely was a child to develop polio if he or she were vaccinated?

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Quizplus · Accepted Answer

The risk of developing polio in the placebo group was 142/201,229, and in the vaccine group, it was 57/200,745. The relative risk is (57/200,745) / (142/201,229), which is approximately 0.4, indicating that vaccinated children were about 3 times less likely to develop polio.

Jonas Salk's Polio Vaccine Trials of 1954 Involved Giving Placebos