Physician-Level Variation in Adenoma Detection and Its Relationship with Procedural Volume: A 12-Year Longitudinal Analysis

Background/Objectives: Adenoma detection rate (ADR) is a central colonoscopy quality indicator, but the extent to which annual procedural volume explains physician-level ADR remains uncertain. We evaluated the association of procedural volume with ADR while separating within-physician annual changes from between-physician differences and explored rank-order persistence of physician-level ADR. Methods: We retrospectively analyzed 36,864 institutional ADR-eligible colonoscopies performed at a Japanese hospital from 2013 to 2024. The canonical dataset comprised 171 physician-year observations from 62 physicians. Weighted physician-year regressions decomposed log annual volume into within-physician and between-physician components. Case-level generalized estimating equations, grouped-binomial models, denominator-restricted analyses, influence analyses, a Bayesian hierarchical logistic model, and an exploratory restricted cubic spline analysis were used as complementary analyses. Results: The examination-weighted ADR was 52.7%, and median annual volume was 188 examinations. In the primary model, the within-physician coefficient was −0.003 (95% confidence interval [CI], −0.039 to 0.033; p = 0.882), corresponding to an estimated ADR difference of −0.19 percentage points per doubling of annual volume (95% CI, −2.69 to +2.31). The between-physician coefficient was 0.027 (95% CI, −0.012 to 0.067; p = 0.177), corresponding to +1.90 percentage points per doubling of usual volume (95% CI, −0.86 to +4.66). Grouped-binomial and denominator-restricted analyses did not identify a positive within-physician association. An exploratory pooled spline suggested curvature at lower volumes, but the overall spline association was not statistically significant. Conclusions: No positive within-physician association between annual procedural volume and ADR was identified. The between-physician estimate was imprecise and did not exclude a potentially meaningful positive association. Annual procedure counts should not be used alone as a surrogate for detection quality; direct longitudinal monitoring of ADR with attention to denominator size, uncertainty, case mix, and modifiable examination processes remains necessary.