In Japan, the National Health Insurance (NHI) prices of new drugs are set according to the NHI Drug Price Standard (NHI Price Standard). The NHI Price Standard was notified by the Ministry of Health, Labour, and Welfare based on the ”Drug Price Calculation Criteria” proposed by the Central Social Insurance Medical Council (Chuikyo) in Japan. The NHI Price Standard affects the research and development strategy of pharmaceutical companies. In order to discover undetected relationships, the factors influencing the ”drug price” were evaluated through the association rule mining technique. We surveyed the Chuikyo‐documents about NHI price listing over the period October 27, 2006 to February 8, 2007. The number of approved new drugs was 874, while that of drugs completed (”drug price per day”) was 314. The numbers of new compounds corresponding to a drug price per day of ”below 200 yen,” ”between 200 yen and 1,000 yen,” ”between 1,000 and 10,000 yen,” and ”above or equal to 10,000 yen” were 87 (27.7%), 91 (29.0%), 79 (25.2%), and 57 (18.2%), respectively. In the association rule mining method, we observed high lift values of the combined items ”above or equal to 30,000 patients expected to be administrated” and ”drugs affecting sensory organs” in the group of drug price per day below 200 yen. The lift values of the combinations of ”biological preparations” and ”similar efficacy comparison‐based price setting (Ⅱ)” or ”below 30,000 patients expected to be administrated” and ”antineoplastic drug” in the group of ”above or equal to 10,000 yen of drug price per day” were high. These results provide a basis for the development and application of new drugs in Japan.
