Question: "Saliva test predicts labor onset" was the headline of a Reuters Health story that appeared May 23, 2000, at the Yahoo! Health News website. The story described a medical test called SalEst. A positive SalEst test indicates an elevated estrogen level, and this knowledge may help to predict how soon a pregnant woman will give birth because estrogen level increases in the 2 to 3 weeks before delivery. Researchers employed by the manufacturers of SalEst tested 642 women who had been pregnant for 39 weeks. Among the 615 women who delivered before the 42nd week of the pregnancy, about 59% had a positive SalEst test. Among the 27 women who delivered in the 42nd week or later, 33% had a positive SalEst test.
a. Construct a contingency table of counts for the relationship between the SalEst test result and the time of delivery.
b. Which of the two variables that were used to make the contingency table is the explanatory variable, and which is the response variable?
c. Among all 642 women, what percentage delivered before 42 weeks?
d. The article states that if a test result is positive, there is a 98% chance that the woman will deliver before 42 weeks. Based on the contingency table, justify this claim.
e. Among those who had a negative test, what percentage delivered before 42 weeks?
f. Would you advise a pregnant woman to spend $90 for the test? Explain why or why not.