Literature Review of Studies Using the National Database of the Health Insurance Claims of Japan (NDB): Limitations and Strategies in Using the NDB for Research

has increased over time. Researchers need to understand the characteristics of the data to generate quality-assured evidence from the NDB. In this review, we mapped and characterized the limitations and related strategies using the NDB for research based on the descriptions of published NDB studies. To find studies that used Japanese healthcare claims data, we searched MEDLINE, EMBASE, and Ichushi-Web up to June 2023. Additionally, we hand-searched the NDB data publication list from the Ministry of Health, Labour and Welfare (2017-2023). We abstracted data based on the NDB data type, research themes, age of the study sample or population, targeted disease, and the limitations and strategies in the NDB studies. Ultimately, 267 studies were included. Overall, the most common research theme was describing and estimating the prescriptions and treatment patterns (125 studies, 46.8%). There was a variation in the frequency of themes according to the type of NDB data. We identified the following categories of limitations: (1) lack of information on confounders/covariates, outcomes, and other clinical content, (2) limitations regarding patients not included in the NDB, (3) misclassification of data, (4) lack of unique identifiers and register of beneficiaries, and (5) others. Although the included studies noted several limitations of using the NDB for research, they also provided some strategies to address them. Organizing the limitations of NDB in research and the related strategies across research fields can help support high-quality NDB studies.