In a cross-sectional study, prevalence of hypertension was higher among those with longer sleep duration. However, this association disappeared after adjusting for age. This is an example of:
- A Effect modification
- B Berkson's bias
- C Confounding ✓
- D Information bias
Correct answer: C. Confounding
Explanation
Confounding occurs when a third variable (age) is associated with both the exposure (sleep duration) and outcome (hypertension) and distorts the apparent association. Since the association disappeared after adjusting for age, age was acting as a confounder — older age is associated with longer sleep time and independently with higher hypertension prevalence. Effect modification would show different effect sizes in different age strata rather than the association disappearing completely.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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