1 Respondent and methods
1.1 Respondents
The number of left-behind children in western China is large [21]. This region is a large agricultural area, an old industrial area, and an economically poor area, which makes the mental health problems of local teenagers face more challenges. Therefore, the study takes primary and secondary school teenagers as the object of study in this region.
This study is a multicenter cross-sectional study conducted in western China from January 2020 to January 2021. The study takes cities, districts, and schools as sampling units, and uses a random cluster sampling method to involve 10–17 years old students from 50 schools in Sichuan Province and surrounding provinces and cities. Inclusive criteria: 1. Students aged 10 to 17;
Exclusion criteria: 1. Unable to accept the investigation due to mental illness; 2. Combined with other serious diseases; 3. Parents and themselves refuse this investigation; 4. Experienced major stress events (such as family breakdown and parents' death) in the past year.
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 the 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 school other than the one selected for the survey. Before the formal investigation, principals of all selected schools were organized to attend a symposium where the significance, workflow, precautions and quality requirements of this survey were introduced.
The survey process is as follows: invite relevant experts inside and outside the hospital to participate in the questionnaire design, establish the initial questionnaire, and generate the final questionnaire after three rounds of discussion. Set up a special investigation team to conduct questionnaire training for the investigators, inform them of the purpose, significance and precautions of the investigation, unify the investigation procedures and methods, and undertake the on-site investigation only after passing the training. During the investigation, we communicated with the principals, teachers and students of the schools under investigation in advance to obtain support and cooperation. During the investigation, the class was the unit, and with the assistance of the head teacher, the questionnaire was distributed by the investigators. Before the subjects were filled in, we used unified guidelines to explain the purpose and significance of the investigation, filling methods and precautions, and told them that the investigation was anonymous, so as to ensure that the research data was true and effective. All the questionnaires were completed by the students themselves on the spot within the specified time and checked by the investigators before they were taken back. All respondents and guardians were investigated with written informed consent.
The survey was conducted anonymously. Four investigators timely reviewed the data and entered it into Excl, deleted the questionnaires with missing key information, missing questionnaires or the same answers, and checked and handled the missing and abnormal values to ensure the accuracy of the data. A total of 21433 questionnaires were collected in this survey, including 19258 valid ones and 19258 invalid ones, with an effective rate of 89.9%. After the inclusion and exclusion criteria, a total of 13784 questionnaires were included in the further study.
1.3 Research instrument
The survey was conducted with a self-made questionnaire on general information, depression-anxiety-stress scale 21 (DASS-21) and coping style scale for middle school students (CSSMSS).
The depression-anxiety-stress scale 21(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 points; "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. The coefficient and retest reliability of Cronbach's α of the Chinese version of the scale are 0.912 and 0.751, respectively, with high reliability and validity.[22].
The coping Style Scale for Middle School Students (CSSMSS) consists of two sub-scales. One is the "problem-focused coping" sub-scale which includes the three factors of "problem-solving", "seeking social support" and "positive and rationalized explanation". The other is the "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. The reliability and validity of the scale are good. Cronbach α coefficient of the total scale is 0.92, and the coefficient of retest reliability is 0.89[23].
1.4 Indices and their definitions
Previous studies have shown that negative emotions and negative coping styles are important influencing factors of NSSI. The NSSI model indicates that psychological or self-regulation factors are considered as the proximal and core factors of self-injury[11]. Therefore, the following seven risk factors are set according to previous literature [15–17] 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) [24].
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 [25].
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. Adolescents who harm themselves at least once in that way without the intention to die in the past year are considered as NSSI behaviors.
1.6 Statistical analysis
The 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 Non-parametric test (Kruskal- Wallis rank sum test) was used to compare the distribution of combined risk factors in different populations. 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).