In the survey, the trained interviewer5 introduced himself or herself and explained the survey purpose and survey topics to the students in each sampled room. Also, the following aspects were made clear before a student agreed to participate in the survey: (a) the survey was voluntary; (b) the survey was confidential;6 (c) participants should independently answer the questions; and (d) after the questionnaire was completed, each respondent would get a small gift from the survey organizer.