A researcher wants to study the causal pathway between childhood malnutrition, adult poverty, and adult cardiovascular disease. She finds that adult poverty is associated with both malnutrition history and cardiovascular disease, but is itself a consequence of early childhood disadvantage. In the directed acyclic graph (DAG) framework, adult poverty in this scenario is BEST described as:
- A A confounder requiring adjustment
- B An effect modifier
- C A mediator on the causal pathway ✓
- D An instrumental variable
Correct answer: C. A mediator on the causal pathway
Explanation
A mediator lies on the causal pathway between the exposure (childhood malnutrition) and outcome (cardiovascular disease), transmitting some or all of the effect. Adjusting for a mediator blocks part of the causal path and underestimates the true total effect — this is the mediator-as-confounder fallacy. A confounder is associated with both exposure and outcome but is not caused by the exposure. An effect modifier changes the magnitude of association across strata. An instrumental variable is associated with exposure but affects outcome only through exposure.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.