Risk ratio, Cofounder

Risk ratio, Cofounder

A study followed 900,000 US adults from 1992 to 2008. At baseline, all participants were screened and determined to be cancer free and their body mass index (BMI) was calculated. Body mass index is a measure of obesity that is calculated using a persons height and weight. Subjects were separated into the following groups according to their BMI: (a) normal weight, (b) slightly overweight, (c) moderately overweight and (d) greatly overweight. 57,145 deaths from cancer occurred in the population during the follow-up period. . The following results were seen for men and women when the heaviest members of the cohort (greatly overweight) were compared to those with normal weight:
Men: Risk ratio of cancer death = 1.5, 95% confidence interval = 1.12.1
Women: Risk ratio of cancer death = 1.6, 95% confidence interval = 1.41.9

    State in words your interpretation of the risk ratio given for the men.
    State in words your interpretation of the risk ratio given for the women.
    Are these results confounded by gender?
    The authors stated that they controlled for confounding many risk factors using a multivariate analysis. State an alternative method that the authors could have used to control for confounding in the design or analysis. In addition, name two confounding variables that you think should be controlled using this method.


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?