A case-control study is performed to study the relationship between esophageal cancer and an exposure (exposure A). Esophageal cancer is a very rare disease (prevalence <<< 1%) in the general population. The cases were 100 persons with the cancer of whom 30 had exposure A. The cases were a random sample of individuals with cancer in the population. The controls were 200 persons without the cancer of whom 18 had exposure A The controls were a random sample of individuals without cancer in the population. Fisher's exact test gave a p-value of .01. What is the estimated odds ratio of cancer for those who had exposure A relative to those who did not have exposure A?

a.1.7
b.2.5
c.3.3
d.4.3
e.6.3
f.None of the above, because odds ratios can never be estimated from a case-control study.

5. Refer to the information given in problem 4, which of the following is the only possible confidence interval for the (population level) odds ratio of cancer for those who had exposure A relative to those who did not have exposure A?

a. 0.8 to 2.1
b. 1.7 to 3.2
c. 2.3 to 8.2
d. - 1.2 to -0.3
g.None of the above, because neither an odds ratios nor a confidence interval for an odds ratio can be estimated from a case-control study.

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