Participants
The inclusion criteria for participation in the study were (1) student in grades 7–12 in the selected school district; (2) obtaining parental permission and providing assent; (3) male; and (4) being resident of Chongqing. The exclusion criteria were: (1) students with mental illness and (2) writing difficulties. Chinese secondary education included junior middle school and high school. Grades 7–9 comprise junior middle school, and grades 10–12 are high school. Considering the low smoking prevalence in female students in China, this study only focused on male students to investigate typical smoking-related characteristics.
Ethical approval
We obtained written informed consents from all parents or main caregivers of the enrolled students through parent–teacher conferences. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of Chongqing Medical University.
Methods
Stratified cluster sampling method was used. Chongqing is one of the municipalities directly under the central government, and it is located in the southwest region of China. After contacting 10 schools in Chongqing, three schools agreed to participate in the study: one school in Bishan County, one in Banan District, and one in Yubei District. Each class from grades 7–12 was randomly selected for data collection. After obtaining the parental informed consents, data were collected through self-administered anonymous questionnaires survey completed by the students.
Questionnaire
The questionnaire was derived with reference to the China Youth Tobacco Survey (China CDC 2015). We modified the questionnaire according to the results of the pilot study among the target subjects, especially on the presentation of questions and further improved the response options of the questions. Questionnaire domains included demographic characteristics, smoking status, smoking-related knowledge, and parental smoking status.
Demographic characteristics
Demographic data included age, school status (middle/high school students), smoking status of parents (non-smoker/smoker), family structure (non-parent families/Single-parent families), per capita household income [high (>5000 ¥), average (1500–5000 ¥), and low (<1500 ¥)] (1 USD = 6.65 ¥).
Smoking-related knowledge
Smoking-related knowledge included nine items: (1) whether smoking causes lung cancer (yes/no), whether smoking causes chronic bronchitis (yes/no), whether smoking causes Laryngeal cancer (yes/no), whether smoking causes heart disease (yes/no), whether smoking causes peptic ulcer (yes/no), whether smoking causes cerebral stroke (yes/no); (2) the way that you get smoking-related knowledge [Television (yes/no)/Teachers (yes/no)/Internet (yes/no)/School (yes/no)/Parents (yes/no)/Newspaper (yes/no)/Friends (yes/no)]; (3) nicotine is a kind of addictive substances(yes/no); (4) smoking has a direct effect on the health (yes/no); (5) pregnant women smoking are harmful to fetus (yes/no); (6) smoke-free environment is helpful to health (yes/no); (7) second-hand smoking is harmful to health (yes/no); (8) smoking whether has effects on physiologic, appearance, social and economy(yes/no); (9) your attitude towards family member smoking (Agree/Neutral/Disagree); your attitude towards family smoking (Agree/Neutral/Disagree); and your attitude towards friends smoking (Agree/Neutral/Disagree).
Hobbies
To assess hobbies, we asked: “Do you have the following hobbies? Reading (yes/no), music (yes/no), Painting (yes/no), online games (yes/no), sports (yes/no), tourism (yes/no)”.
Smoking status
Smoking status was determined by asking respondents whether they were smokers. Current smoker was defined as a person who smoked tobacco at the time of the interview. Assessing the smoking status of parents was conducted the same way. Participants were asked the following questions: “Does your father smoke? (yes/no)” and “Does your mother smoke? (yes/no)”.
Methods of data collection
In June 2014, a formal survey was conducted in main urban areas of Chongqing. At each survey location, participants who had met the inclusion criteria completed the questionnaires. The investigating team members audited the questionnaire on the spot for completeness and corrected the error before collecting the questionnaires. A total of 1297 completed questionnaires were collected after distributing 1370 questionnaires in the three schools of Bishan Country (300/320), Banan District (526/550) and Yubei District (481/500), with overall response rate of 94.7%.
Pilot test
The pilot test was conducted with 50 students in a middle school that did not participate in the current study. We modified the questionnaire according to results of the pilot test, especially on the presentation of questions.
Data collector and training
Nine medical students of Chongqing Medical University were recruited to collect data. The data collectors were trained. Investigation site was coordinated by the investigator. Data collection process entailed explaining to the students that the questionnaire was anonymous and steps were taken to ensure the authenticity and reliability of the questionnaire.
Data processing and analyses
Frequencies were calculated for all categorical variables and means and standard deviations were computed for all metric variables. Comparison between groups was conducted using χ2 test, and generalized estimating equation for statistical analysis. Generalized estimating equation (GEE) (Liang and Zeger 1986; Liu and Zhang 2006) was used to probe factors that affect sources of smoking-related knowledge, which including television, teachers, internet, school, parents, newspaper, and friends. Generalized estimating equation to probe factors affects smoking-related diseases, which including lung cancer, chronic bronchitis, laryngeal cancer, heart disease, peptic ulcer, and cerebral stroke. Statistical tests included a two-sided test, and statistical significance was considered at p < 0.05. All data were analyzed the Statistical Package for Social Sciences (IBM-SPSS), Version 22.0.