‘Large-N Paradox: geographic bias in clinical evidence

Epidemiology relies on the accurate evaluation of external validity, yet the dissemination of clinical evidence remains structurally skewed by geography. We identify a ‘Large-N Paradox’, where non-Western clinical registries with massive sample sizes and high representativeness are systematically filtered into specialty journals, while smaller Western cohorts frequently appear in top-tier general medical journals.

Japan’s mature clinical registries illustrate this global asymmetry. The National Clinical Database (NCD) archives over 2.6 million surgical cases annually, and the J-ASPECT (stroke) and J-PCI (cardiology) registries analyse approximately 300 000 cases each per year.1 2 Unlike many voluntary Western registries that are prone to selection bias, these Japanese databases mandate data entry and enforce rigorous on-site random audits to ensure population-level representativeness.3

Despite this methodological rigour, a ‘Scale versus Impact’ analysis reveals a structural disparity (figure 1). High-volume, high-validity Asian datasets are often rejected by high-impact general journals under the premise…

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