1. (1) Nagano Prefectural Police Agency: Traffic Accidents Statistics 2017 (2018).
2. (3) Institute for Traffic Accident Research and Data Analysis: Traffic Accident Statistics Annual Report 2014 (2015).
3. (4) Institute for Traffic Accident Research and Data Analysis: Traffic Accident Statistics Annual Report 2015 (2016).
4. (5) Institute for Traffic Accident Research and Data Analysis: Traffic Accident Statistics Annual Report 2016 (2017).
5. (6) Meitetsu Kim: Data Science Using R (Second edition), Morikita Publishing, pp.60-73 (2017).