In a study (47) investiga ting the effect of rubella infections (German measles) on childbirth, a total of 578 pregnancies were classified in relrospecl as having been either "normal" or "abnormal," the latler group including abortions, stillbirths, birth defects, and all infant deaths w"1thin two years. Altogether, there were 86 abnonnal pregnancies. The second variable looked at was when the rubella infection occurred-during the first trimester or after the first trimester. It was found that 59 of the 86 abnormal births were among the 202 pregnancies complicated during the first trimester; the remaining 27 were born to mothers who contracted the virus after the first trimester. Can it be concluded that the risk of an abnormal birth is dependent on when during the pregnancy the virus is contracted? Let a = 0.01.