Bias And Confounding Practice Test

Researchers are studying the relationship between alcohol consumption and risk of myocardial infarction (MI). They find a crude odds ratio of 2.5. They suspect that smoking may be a confounding factor, as it is associated with both alcohol use and MI. They perform a stratified analysis based on smoking status. In smokers, the odds ratio for alcohol and MI is 1.2. In non-smokers, the odds ratio is 1.1.

A pharmaceutical company develops a new screening test for a slow-growing cancer. In a trial, the group screened with the new test has an average 5-year survival of 75% after diagnosis, while the group receiving standard care has a 5-year survival of 60%. However, the overall mortality rate from the cancer is identical in both groups over a 20-year follow-up period.