Funding for this research was provided by:
Japan Society for the Promotion of Science (26245039 and 26380365)
Received: 16 October 2017
Accepted: 3 April 2018
First Online: 13 April 2018
Ethics approval and consent to participate
: We used data from “The Longitudinal Survey of Middle-aged and Older Adults,” conducted and released by the Japanese Ministry of Health, Labour and Welfare. Japan’s Statistics Act (2007) required the survey to be reviewed from statistical, legal, ethical, and other viewpoints. We obtained the survey data from the Ministry with its official permission, and so the current study did not require ethical approval. The need for written consent was waived in line with the Statistics Act.
: The authors declare they have no competing interests.
: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.