Suicide among young-old and old-old adults in rural China: A case-control psychological autopsy study.

According to the ICMJE, purely observational studies (those in which the assignment of the medical intervention is not at the discretion of the investigator) will not require registration. Our study was not registered because this is a case-control study. But all procedures of the study were carried out in accordance with the latest version of the Declaration of Helsinki. The study were approved by the Institutional Review Boards of the Central South University, Shandong University, and Guangxi Medical University.