In the Bradford Hill criteria, 'biological gradient' refers to:

• A The association being consistent across multiple studies in different populations
• B The association being biologically plausible based on known mechanisms
• C The effect reversing when the exposure is removed
• D A dose-response relationship where greater exposure produces greater effect ✓

Explanation

Biological gradient (Hill's 5th criterion) is the dose-response relationship — as the amount of exposure increases, the risk of disease increases proportionally. This strengthens causal inference because it demonstrates that the exposure quantitatively drives the outcome. Consistency refers to replication; plausibility is a separate criterion; reversibility is coherence/experiment.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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