Data collection

Three research assistants were hired for this study to collect data, including two graduate students and one nurse practitioner. Before the formal investigation, they were trained on study protocol and explanation of questionnaire items by the principal researcher. Finally, they took a test on the study protocol and questionnaire content with a passing score of 90 or above. All three research assistants passed the exam and were allowed to participate in this study.

From October to December 2020, a total of 800 college students aged 17–23 years old from four universities were recruited in Zhengzhou, Henan Province, China. A stratified cluster random sampling method was used according to the students’ major and class. In each university, one class was selected at random according to the grade level. The study took place after class. The research assistants explained the purpose and significance of the study to the participants. All participants received informed consent before enrolling in the study and were guaranteed voluntary participation, withdrawal, study risks, confidentiality, and secured data storage.