In the initial test of the Salk vaccine for polio 400,000 children were selected and divided into ...

In the initial test of the Salk vaccine for polio 400,000 children were selected and divided into two groups of 200,000. one group was vaccinated with the Salk vaccine while the second group was vaccinated with a placebo. of those vaccinated with the Salk vaccine 33 later developed polio. of those receiving the placebo 115 later developed polio. test the claim the Salk vaccine is effective in lowering the polio rate. use a=0.01 state the conclusion.