What the Controlled-Vocabulary Layer Cannot Say About Where a Depression Biomarker Was Measured: A Meta Research Analysis of MeSH Sampling-Compartment Coding, January 2024-June 2026

Background

Peripheral biomarkers for major depressive disorder are accessible but correspond poorly to central nervous system processes, a point the evidence base can address only if its record registers the compartment in which each marker was measured. To determine, by meta research rather than evidence synthesis, whether the indexed record of recent depression biomarker research registers the peripheral-central distinction, separating omission by indexers from absence mandated by the controlled vocabulary. That peripheral markers are imperfect proxies for central processes is established prior knowledge; the question here concerns the bibliographic infrastructure through which that literature is retrieved.