Acknowledgements
The authors thank Ms. Kahori Sano, Sachiko Ichimura, and Azusa Sakamoto for secretarial assistance.
Author contributions
Conception/design: JI, HI, KO, and TK. Provision of study materials: JI, HI, KO, and TK. Data collection and analysis: All authors. Manuscript writing: JI, HI, and TK. All the authors have read and approved the manuscript.
Disclosure statement
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.