Association Between Duration of Usual Source of Care and Patient-reported Primary Care Quality in Japan: A Nationwide Cross-sectional Study

Objectives: High-quality primary care is associated with improved patient experience (PX). Continuity of care is a driver of PX but often relies on complex indices. Whether a simple measure—years of attendance—captures PX remains unclear, especially in free-access systems lacking formal registration such as Japan, South Korea, and Germany. We aimed to investigate the association between “years-of-attendance” and PX, measured by the validated Japanese Person-Centered Primary Care Measure (PCPCM), among adults with a usual source of care (USC). Methods: In 2022, we conducted a nationwide, cross-sectional, web survey of Japanese adults (20-74 years). Of 800 respondents (response rate: 71.9%), we analyzed data from the 423 participants who reported having a USC. Exposures were log-transformed years since respondents began visiting their usual institution and physician. The outcome was the mean PCPCM score (11 domains, range: 1-4). Multivariable linear regression adjusted for age, sex, education, household income, self-rated health, number of chronic conditions, type of USC (clinic vs hospital), and rurality. We conducted stratified analyses by type of USC (clinic vs hospital) and rurality (urban vs rural/remote) to assess contextual robustness. Results: The median PCPCM was 2.47. Longer continuity showed a positive, dose-responsive association with PCPCM scores. The effect was strongest for physician-level continuity (β = .20, 95% CI: 0.09-0.31, P < .001). Stratified analyses revealed that the continuity-PX gradient was steepest for clinics in urban settings and hospitals in rural or remote settings. Conclusions: Among Japanese adults with a USC, longer continuity correlates with better PX. “Years of attendance” works as a practical quality indicator, with interpersonal continuity mattering more than institutional continuity. These findings do not extend to adults without a USC and should be interpreted within this population. Future longitudinal studies are required to inform policies aimed at sustaining continuity.