A recent study compared 298 children with Autism Spectrum Disorder to 1507 randomly selected control children without the disorder. Of the children with autism, 20 of the mothers had used antidepressant drugs during the year before pregnancy or the first trimester of pregnancy. Of the control children, 50 of the mothers had used the drugs.

(a) Is there a significant association between prenatal exposure to antidepressant medicine and the risk of autism? Test whether the results are significant at the 5% level.

(b) Can we conclude that prenatal exposure to antidepressant medicine increases the risk of autism in the child? Why or why not?

(c) The article describing the study contains the sentence ‘‘No increase in risk was found for mothers with a history of mental health treatment in the absence of prenatal exposure to selective serotonin reuptake inhibitors [antidepressants].” Why did the researchers conduct this extra analysis?