How chronic pain is defined matters: Prevalence estimates and health-related quality of life under alternative definitions.

Background: Chronic pain is a leading cause of long-term disability, yet prevalence estimates vary widely due to differences in operational definitions. Although a 3-month duration criterion is commonly used, it may not adequately reflect the functional burden of chronic pain. This study compared prevalence estimates derived from alternative chronic pain definitions and evaluated which best identify individuals with impaired health-related quality of life (HRQoL). Methods: Data were drawn from a population-based sample of adults (n = 5557). Pain was assessed using the Brief Pain Inventory, and HRQoL was measured with the Short Form 12 Health Survey (SF-12v2). Six definitions were examined: duration-only (≥3 months), pain pattern (constant or daily intermittent), pain severity thresholds (≥3 and ≥4), and pain interference thresholds (≥3 and ≥4). Results: Prevalence estimates varied substantially by definition, ranging from 40.1% using duration alone to 12.0% using pain interference ≥4. Increasingly restrictive definitions were associated with progressively lower physical and mental health scores. Effect sizes for physical health impairment increased from Cohen's d = 0.81 for the duration-only definition to 1.68 for the most restrictive interference-based definition. Definitions incorporating pain interference most clearly distinguished individuals with reduced HRQoL. Conclusions: The operational definition of chronic pain strongly influences both prevalence estimates and identification of clinically meaningful impairment. Definitions incorporating functional impact more accurately identify high-burden chronic pain than duration alone, supporting the integration of temporal and functional dimensions in standardised definitions.