Funding for this research was provided by:
Japan Society for the Promotion of Science (17H00991 and 18K19699)
Text and Data Mining valid from 2019-12-01
Received: 3 October 2019
Accepted: 23 December 2019
First Online: 30 December 2019
Ethics approval and consent to participate
: We obtained the CSLC data with permission from the MHLW. The CSLC was authorized by the Ministry of Internal Affairs and Communications, which is in charge of all government surveys in Japan, from the statistical, legal, ethical, and other viewpoints in accordance with the Statistics Law in Japan. Hence, ethics approval was not required for the current study. The need for written consent was waived in line with the Statistics Act.
: Not applicable.
: The authors declare no competing interests.