The Salk Vaccine Trials of 1954 included a randomized controldouble blind study in which elementary school children ofconsenting parents were assigned at random to injection with theSalk Vaccine or a placebo. Both treatment and control group wereset at 200,000 because the target disease , infantile paralysis(POLIO) was uncommon, but in many cases deadly. The number in thecontrol group ended up to be 199,858 and the number in thetreatment group ended up to be 199,944. Dropouts for variousreasons in field trials are common for various reasons. At the endof the study there were 142 polio cases in the control group and 56polio cases in the treatment group. The actual study is moreinteresting than this because there were degrees of severity ofpolio cases ranging from mild cold symptons to death (sounds like avirus going around now but less contagious).

a) This study is:

a) Retrospective experiment

b) Retrospective observationalstudy

c) Retrospective observationalstudy

d) Prospective experiment

b) Test the hypothesis that the proportion of polio cases isless in the treatment group than in the control group and stateyour conclusion

c) Use a test to determine whether there is any relationshipbetween the cases of polio and the treatment (vaccine or control).State your hypothesis, test statistic, p-value , andconclusion.

d) How are the hypotheses tested in b) and c) related?