[Abstract]The National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB) is the large and nationwide database which is composed of 25 billion of claims data for more than 120 million people in the entire country and the government opened it to Japanese researchers for 13 years since 2011. As the NDB includes nearly all claims data in this country, it is unprecedentedly big real-world data with completeness in the world. In this article we introduce how to utilize the NDB resources in clinical research as well as epidemiology. For example, we extracted all cases with rheumatoid arthritis who received eight molecular targeted drugs and compared the retention rates and occurrence of opportunistic infections between the drugs. We also discovered the seasonal change of the number of new cases for these therapy by using big data.

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