In a large case-control study of patients with pancreatic cancer, 17% of the patients were found to be diabetic at the time of diagnosis, compared with 4% of a well-matched control group (matched by age, sex, ethnic group, and several other characteristics) that was examined for diabetes at the same time as the cases were diagnosed. It was concluded that the diabetes played a causal role in the pancreatic cancer. This conclusion:a. Is correctb. May be incorrect because there is no control or comparison groupc. May be incorrect because of failure to establish the time sequence between onset of the diabetes and diagnosis of pancreatic cancerd. May be incorrect because of less complete ascertainment of diabetes in the pancreatic cancer casese. May be incorrect because of more complete ascertainment of pancreatic cancer in non-diabetic persons
C – may be incorrect b/c of failure to establish time sequence between onset of diabetes and diagnosis of pancreatic cancer
The correct answer is C. The conclusion that diabetes played a causal role in the pancreatic cancer may be incorrect because of a failure to establish the time sequence between onset of the diabetes and diagnosis of pancreatic cancer. The study design is a case-control study, which is useful for exploring potential associations between exposure and disease, but it cannot establish causality. In this study, the researchers found a higher proportion of patients with pancreatic cancer had diabetes at the time of diagnosis compared to the control group. However, it is not clear whether diabetes preceded the onset of pancreatic cancer or developed as a result of it. To establish a causal relationship, a prospective cohort study or a randomized controlled trial would be needed.
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