Question

EPIDEMIOLOGY QUESTION

60. Investigators explored the relationship between coffee drinking and osteoporosis using a case-control study. They calculated the overall odds ratio and odds ratios among smokers and non-smokers. The results are shown below. OR (overall) = 2.20 OR (smokers) = 5.0 OR (non-smokers) = 1.0 In this example, would smoking be best considered an effect modifier, mediator, or confounder for the relationship between coffee consumption and osteoporosis? A. Confounder B. Mediator C. Effect modifier

Answer 1

There is an association between an exposure (coffee drinking) and a disease (osteoporosis), but we wonder whether cigarette smoking could be a confounder of this relationship.

STEP 1. IS THERE AN ASSOCIATION?

Heavy coffee drinking is associated with higher rates of osteoporosis (OR = 2.20). Is coffee then a cause of osteoporosis?

STEP 2. IDENTIFY POTENTIAL CONFOUNDERS:

Could cigarette smoking be a confounder?

STEP 3. IS THE POTENTIAL CONFOUNDER ASSOCIATED WITH THE EXPOSURE?

Heavy coffee drinking is associated with higher rates of smoking. Smoking fulfills one criterion for potential confounding.

STEP 4. IS THE POTENTIAL CONFOUNDER ASSOCIATED WITH THE DISEASE OF INTEREST?

Smoking is associated with higher rates of osteoporosis. Smoking fulfills the second criterion for potential confounding.

STEP 5. WHAT HAPPENS WHEN WE CONTROL FOR CIGARETTE SMOKING?

Adjustment for cigarette smoking eliminates the association of heavy coffee drinking and osteoporosis (OR = 5 for smokers while OR = 1 for non smokers. The association is explained by the fact that more coffee drinkers are also smokers.

CONCLUSION: COFFEE DRINKING IS NOT A CAUSE OF MYOCARDIAL OSTEOPOROSIS

This means smoking is confounder for the relationship between coffee consumption and osteoporosis

Option A is correct