1. A case-control study was performed to determine whether head injury was associated with an increased risk of brain tumors in children. 200 cases with brain cancer were identified from the state cancer registry and 200 controls were recruited from the same neighborhoods where the cases lived. The mothers of the children completed a questionnaire that asked them to describe their child’s past history of head injury. The investigators found that the mothers of the children with brain tumors reported a past head injury for 70 of the cases while a past history of head injury was reported in 30 of the controls. What type of bias was likely to have influenced the findings of this study, and why? What can be done to minimize this type of bias?
QUESTION 2
1. A study used self-administered mail questionnaires to gather data on height and weight in order to calculate a measure of obesity. Which of the following types of problems were likely avoided by this method of data collection, and why?
· Interviewer bias
· Exposure misclassification
· Confounding
· Selection bias
· Loss-to-follow-up
1. Consider each of the following scenarios and state whether or not the variable in question is a confounder, and why.
· A study of the risk of pulmonary hypertension among women who take diet drugs to lose weight. The crude relative risk of pulmonary hypertension comparing diet drug users to non-users is 17.0 and the age adjusted relative risk is 5.0. Is age a confounder in this study?
· A cohort study of liver cancer among alcoholics. Incidence rates of liver cancer among alcoholic men are compared to a group of non-alcoholic men. Is gender a confounder in this study?
· A case-control study of the risk of beer consumption and oral cancer among men. In this study, cigarette smoking is associated with beer consumption and is a risk factor for oral cancer among both beer drinkers and nondrinkers. Is cigarette smoking a confounder in this study?
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