For several years, evidence had been mounting that folic acid reduces major birth defects. In a study, doctors enrolled women prior to conception and divided them randomly into two groups. One group, consisting of

2765

women, took daily multivitamins containing 0.8 mg of folic acid; the other group, consisting of

2065

women, received only trace elements. Major birth defects occurred in

34

cases when the women took folic acid and in

52

cases when the women did not.

a.

At the10%significance level, do the data provide sufficient evidence to conclude that women who take folic acid are at lesser risk of having children with major birth defects?

b. Is this study a designed experiment or an observational study? Explain your answer.c. In view of your answers to parts (a) and (b), could you reasonably conclude that taking folic acid causes a reduction in major birth defects? Explain your answer.

• Calculate the z____
• Calculate the P____