Ethical considerations
This study was approved by the Ethics Committee of Hainan Medical University (Approval number: HNLL-2020-54; approval date: March 17, 2020). When the subjects were enrolled, researchers used standardized instructions to introduce the purpose, significance, and methods of this study in detail and ensured that the subjects had been informed consent regarding the entire study process, voluntarily participated in the study, and signed the hard copies of an informed consent form. The study was designed so that it would not infringe on the rights and interests of the research subjects, and the subjects could withdraw from the study at any time.