a. A study of the relationship between exercise and heart attacks that is conducted among women who do not smoke. Explain whether gender is a confounder.
b. A case-control study of the relationship between liver cirrhosis and alcohol use. In this study, smoking is associated with drinking alcohol and is a risk factor for liver cirrhosis among both non-alcoholics and alcoholics. Explain whether smoking is a confounder.
a. How can gender be a confounder, if only one gender is used?
b. Would the cirrhosis found be caused by drinking, smoking or an interaction of the two? (An ANOVA could separate out the effects of these factors.)
Does answering those questions help you?
a. In this study, gender is not a confounder. This is because the study is specifically focused on women who do not smoke, which means that gender is already controlled for as an exclusion criterion. When a study is conducted within a specific subgroup, such as women who do not smoke in this case, gender is no longer a confounding variable because it is being intentionally controlled for. Therefore, any observed relationship between exercise and heart attacks within this subgroup can be attributed to the variable of interest (exercise) without being confounded by gender.
b. In this case-control study, smoking can be considered a confounder. A confounder is a variable that is associated with both the exposure (drinking alcohol) and the outcome (liver cirrhosis) and can distort or modify the relationship between the exposure and outcome. In this study, smoking is associated with both alcohol use and liver cirrhosis among both non-alcoholics and alcoholics. Therefore, smoking in this context can potentially confound the relationship between alcohol use and liver cirrhosis.
To determine if smoking is indeed a confounder, researchers would need to assess the relationship between alcohol use and liver cirrhosis while controlling for the potential effect of smoking. This can be done by performing stratified analyses or using statistical techniques such as multiple regression analysis to adjust for the effect of smoking on the relationship between alcohol use and liver cirrhosis. By carefully accounting for the potential confounding effect of smoking, researchers can better understand the true relationship between alcohol use and liver cirrhosis in this case-control study.