Funding for this research was provided by:
Japan Society for the Promotion of Science (17H00991 and 18K19699)
Received: 21 October 2019
Accepted: 2 April 2020
First Online: 15 April 2020
Ethics approval and consent to participate
: The CHARLS dataset, which was used in this study, was publicly available (ExternalRef removed), and its study protocol was approved by the Ethical Review Committee of Peking University, China. Hence, ethical approval was not needed for this study. Survey data were obtained from the MHLW, with its official permission. Therefore, the current study did not require ethical approval. The need for written consent was waived by the Committee.
: Not applicable.
: The authors declare no competing interests.