With the methods of stratified sampling and cluster sampling, primary and secondary school students who met the research standards were randomly selected as survey subjects. Inclusion criterion: 1) students aged from 10 to 17 years old;
Exclusion criteria: 1) students who were unable to participate in the survey due to mental or psychological problems; 2) students who contracted other serious diseases; 3) students, as well as their parents, who refused to attend the survey.
1.2 Research Methods
Under the organization and coordination of Nanchong Municipal Bureau of Education and Sports, the on-site survey was jointly carried out by Psychological Crisis Intervention Working Group of Mental Health Center in the Affiliated Hospital of North Sichuan Medical College, together with the work team. Before the survey, a pilot survey was conducted in a non-selected school, and principles of all selected schools were organized to attend a symposium where the significance, work flow, precautions and quality requirements of this survey were introduced.
The survey process is as follows: upon registering wjx, a platform in China providing functions equivalent to Amazon Mechanical Turk, members of the work team created the preliminary questionnaire and the final one was decided after three rounds of discussion. The link and QR code of the final questionnaire was sent to the principals, through whom the link and code reached the teachers of every school. The link and code were resent to class group by the class teacher and students were able to fill in the questionnaire when their parents clicked the link or scanned the code on We Chat. The questionnaire was required to be completed within a specified time period of ten days. All survey subjects had signed written informed consent form.
The survey was carried out anonymously. Quality review of the questionnaires received was conducted on a day-to-day basis and the questionnaires that failed to meet the requirement were excluded after giving feedback to the working group.
1.3 Research Instrument
The survey was conducted with a self-made questionnaire on general information, depression-anxiety-stress scale (DASS-21) and coping style scale for middle school students (CSSMSS).
The depression-anxiety-stress scale (DASS-21), made up of 3 sub-scales, examines an individual’s experience of depression, anxiety and negative emotions resulting from stress, respectively. Each sub-scale contains 7 items which are graded on a 4-level scale, with “not suitable” as 0 point; “sometimes suitable” as 1 point; “often suitable” as 2 points; “always suitable” as 3 points. The sum of the 7-item scores multiplied by 2 makes the total score of the sub-scale, which ranges from 0 to 42 points. A higher total score indicates severer negative emotions of the survey subject .
Coping Style Scale for Middle School Students (CSSMSS) consists of two sub-scales. One is “problem-focused coping” sub-scale which includes the three factors of “problem solving”, “seeking social support” and “positive and rationalized explanation”. The other is “emotion-focused coping” sub-scale which includes the four factors of “tolerance”, “avoidance”, “venting of emotions” and “denial of fantasy”. Each factor is comprised of several items which are scored on a 4-level scale, with “not use” as 1 point, “use occasionally” as 2 points, “use sometimes” as 3 points and “use frequently” as 4 points. The sum of item scores makes the scores of factors, and the addition of factor scores belonging to the same sub-scale is the score of the sub-scale. Generally the total score of the CSSMSS is not measured .
1.4 Indices and Their Definitions
Seven risk factors were designated with reference to previous literature [9-11] and they are depression (defined as depression dimension score > 9 points in DASS-21), anxiety (defined as anxiety dimension score > 7 points in DASS-21), stress (defined as stress dimension score > 14 points in DASS-21), low social support (defined as social support dimension score ≤ 12 points in CSSMSS, based on the national norm of 16.48±4.04 points), tolerance (defined as tolerance dimension score ≥ 12 points in CSSMSS, based on the national norm of 8.94 ± 2.42 points), avoidance (defined as avoidance dimension score ≥ 10 points in CSSMSS, based on the national norm of 7.23 ± 2.36 points), emotional venting (defined as emotional venting dimension score ≥11 points in CSSMSS, based on the national norm of 7.70±2.50 points) . The clustering of risk factors: according to the number of risk factors, the survey subjects were divided into 4 clusters marked from level 0 to level 3, of which level 0 meant none of the above risk factors was manifested in the subject, and level 3 meant three or more than three risk factors manifested themselves in the subject at the same time .
Judgment of NSSI behaviors: a single-item evaluation method was used to judge NSSI behaviors and the defined NSSI behaviors included hitting one’s head against a wall, biting, picking or scratching oneself hard, pulling one’s hair forcefully, cutting or stabbing oneself with a knife or sharp object, binding oneself and others. The adolescents who harm themselves at least once in that way without the intention to die in the past year are considered having NSSI behaviors.
1.5 Quality Control
(1) Project design: a special investigation team was formed whose members were postgraduates majoring in psychiatry and mental health. Subject seminars were held regularly and experts working for the hospital or external institutes were invited to discuss with team members the subject design, questionnaire design and revision, and subject progress. Investigators were trained with questionnaire survey, so that they were informed of the purpose, significance and precautions of the survey. Investigation procedures and methods were also unified. Only after passing the training could the investigators carry out on-site survey.
(2) Data collection: the principals, teachers and students of the selected schools were reached out in advance to obtain their support and cooperation. With class as unit, the survey questionnaires were handed out under the assistance of head teachers. Before filling in the questionnaire, students were informed of the purpose and significance of the survey, completing methods and precautions. They were also told that the survey was conducted anonymously to ensure the veracity and effectiveness of the data.
(3) Data sorting and input: after recovering data, four investigators would review the data in time and enter them into Excel. The questionnaires with missing key information, incomplete or the same answers were abandoned. Missing and abnormal values were carefully checked and dealt with to ensure data accuracy.
1.6 Statistical Analysis
Database was built with Epidata3.1 and data analysis was conducted with SPSS23.0. The measurement data were described with mean ± standard deviation, the comparison between groups was carried out with student’s test, and the comparison of categorical variables was conducted with chi-square test. Cochran-Armitage trend (CAT) test was used to analyze the trend. During multivariate analysis, by virtue of logistic regression, the dependent variable was whether or not NSSI behaviors occurred, stepwise regression analysis was used to select variables, and the results were expressed as OR (95% CI).