A case-control study was conducted to evaluate the association between alcohol consumption and cancer of the oral cavity. The crude analysis showed a strong association between the exposure and outcome: odds ratio = 4.5, 95% confidence interval 3.4-5.6. Smoking was considered as a potential confounder of the association. Which of the following properties of smoking is necessary in order for it to be considered as a confounder?

Question

A case-control study was conducted to evaluate the association between alcohol consumption and cancer of the oral cavity.  The crude analysis showed a strong association between the exposure and outcome: odds ratio = 4.5, 95% confidence interval 3.4-5.6.  Smoking was considered as a potential confounder of the association.  Which of the following properties of smoking is necessary in order for it to be considered as a confounder?

Quizplus · Accepted Answer

When looking at the effect between an exposure and an outcome, confounding leads to mixing up the effect of the exposure (eg, alcohol consumption) on the outcome (eg, oral cavity cancer) with the effect of an extraneous factor/confounder (eg, smoking) on the outcome (eg, oral cavity cancer). In order to be a confounder, the extraneous factor must have some properties linking it with both the exposure and the outcome of interest. In this example, smoking is the possible confounder. Smoking is related to the exposure (ie, people who consume alcohol are more likely to smoke) as well as the outcome of interest (ie, smoking, by itself, is associated with cancer of the oral cavity). If smoking is the confounder, it explains at least part of the association observed between alcohol consumption and cancer of the oral cavity. (Choice A) If smoking is not related to cancer of oral cavity, it cannot be a confounder in this case. (Choice B) Although a confounder may be prevalent in a population, high prevalence is not a necessary condition for a variable to be considered a confounder. For example, smoking may still be a confounder for the relationship between alcohol consumption and oral cavity cancer even in a population where the prevalence of smoking is extremely low. (Choices D and E) A confounder may be commonly observed both in exposed and unexposed subjects and it is not evenly distributed between the groups. Educational objective: A confounder is an extraneous factor that has properties linking it with both the exposure and the outcome of interest.

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