confounder mediator and effect modifier. 3pptx.pptx

example of confounder, mediator and effect modifier

1. Confounder, Effect Modifier & Mediator Examples Nawshaba Akther Mohona 2421243 1

2. Confounder Example 2: Alcohol drinking and accidents At first glance, alcohol drinking looks strongly linked to road accidents. But people who drive more often at night are more likely to drink and more likely to have accidents because of poor visibility and fatigue. Night-time driving is therefore related to both alcohol use (exposure) and accidents (outcome), but it is not in the causal pathway → making it a confounder. Crude OR = (90×150)/(110×50) = 13500/5500 = 2.45 Cude 2×2 Accident No Accident Alcohol users 90 110 Non-users 50 150 2

3. Stratum Specific Odds Ratio (summary) (Night driving) Crude OR (with Alcohol) Adjusted OR (Rarely) (Sometimes) (Often) Road accidents (Y) 2.45 1.32 1.20 1.35 1.40 The crude OR (2.45) makes alcohol look like a very strong risk factor for accidents. After adjusting for night-time driving, the OR drops to 1.32. The stratum-specific ORs are similar, proving that the crude association was distorted. 3 The difference between crude and adjusted is ≈46% (>10%) while the SSORs are relatively close (1.20–1.40).

4. Effect Modifier Example 2: Flu Vaccine & Flu Illness Explanation: The flu vaccine is protective overall, but much more effective in children and younger adults compared to the elderly. Age modifies the effect of the vaccine. Crude (pooled) 2×2 Flu No flu Vaccinated 40 160 Unvaccinated 60 140 4

5. Stratum Specific Odds Ratio (summary) Interpretation: The protection varies strongly by age: very strong in young people, moderate in adults, and almost absent in elderly. Because the SSORs differ widely, age is an effect modifier in this context. (Age) Crude OR (with vaccine) Adjusted OR Children (5–17) Adults (18–59) Older adults (≥60) Flu 0.58 0.54 0.18 0.32 1.12 Crude vs adjusted ≤10%, SSORs differ a lot (>10%), p significant 5

6. Mediator Example 2: Education → Literacy → Service Use Explanation: Education improves women’s knowledge and awareness (health literacy). This better understanding then motivates them to use maternal health services. Pathway: Education → Health literacy → Maternal health service use Education increases service use through the pathway of improved literacy. Therefore, health literacy is a mediator. 6

7. 7 Thank you