The study was a part of a national questionnaire-based survey called “Youths, Sex and Internet—in a changing world” and was performed at the request of the Swedish Ministry of Health and Social Affairs. The survey was partly a replication of two earlier studies that were carried out in 2004 and in 2009 [27, 28].
The study was carried out in the 3rd and last year of Swedish high school during the fall of 2014. The selection of study sample, distribution and collection of the questionnaire was performed by Statistics Sweden (a national administrative agency). To form the study sample, the National School Register for the 2nd year of Swedish high schools for the fall of 2013 was used. By using stratification on the basis of school size and study program a total of 13,903 adolescents from 261 out of 1215 schools were selected for the study. Of the 261 schools selected, 238 were still providing the selected study programs in 2014. A total of 171 schools with 9773 adolescents agreed to participate in the study. Of the 9773 adolescents that had the opportunity to participate in the study, 5873 completed the questionnaire. Thirty-four questionnaires were excluded due to unserious answers or a high amount of missing data. This gave a response rate of 59.7%. A further 89 did not answer the index question about using sex as self-injury, resulting in a total of 5750 participants for the study. Mean age of the participating adolescents was 18.0 years (SD = .6). According to data from 2014, 91.7% of all Swedish 18 years old adolescents were enrolled in the Swedish high school system .
The study group was selected with the aim of being representative of the 3rd year of Swedish high schools. However, for a separate study concerning Stockholm, an extra sample from the county of Stockholm was included in the study. The additional Stockholm sample showed a lower response rate (48.7%) compared to the rest of the country (65.3%), came more often from middle-size schools with 191–360 pupils (51.2 vs. 41.6%), giving a small effect size (Cramer’s V = .10, χ2 = 63.6, df = 2, p = .000), and were more often studying practical high school programs (33.2 vs 27.7%), giving no effect size (Cramer’s V = .05, χ2 = 17.1, df = 1, p = .000). The Stockholm sample was retained in this study to give a larger and more robust study sample.
Information about the study was sent to the head of each school by mail. Students received written information about the study and gave informed consent for participation by filling in the questionnaire. According to the Ethical Review Act of Sweden, active consent is not required from parents of adolescents’ aged 15 years or older . Participants answered the questionnaire in digital format (by computer, in 165 schools) or, where computers were not available, on paper (6 schools). Regardless of distribution method, anonymity was guaranteed. The study was performed during lecture time in the selected schools during September–November 2014. Reminders were given by phone during November 2014 to those schools that had not yet returned data. With regard to the sensitive topics in the questionnaire, both the head of the school, teachers responsible for the lecture and the participating adolescents received an information letter about the study including contact details for help and support if needed after answering the questionnaire.
The questionnaire for the present study was a modified version of the questionnaire used in 2004 and 2009 [27, 28]. The questionnaire used for this study comprised in total 116 main questions, of which 34 were analyzed in the present study.
The index question for this study was new and literally formulated: “Have you ever used sex to purposely hurt yourself?”. To investigate the occurrence of sex as self-injury, questions included were; age at first occurrence, number of occurrences during the past year and in total, age and gender of the sexual encounter on the previous occasion and the perceived pain of using SASI.
Questions about Sociodemographic factors included gender with the options boy, girl and “The classification ‘male’ or ‘female’ does not fit for me”, parents’ occupation and education, financial situation in the family, immigrant background and living situation.
Sexual behavior and sexual risk-taking, were investigated by questions concerning sexual orientation, voluntary sexual experiences, age at first voluntary intercourse, number of sexual partners, use of contraceptives, occurrence of abortion (self or partner) and sexually transmitted infection of chlamydia. To investigate the occurrence of selling sex, the question used was “Have you ever sold sexual services?”.
The question related to sexual abuse was “Have you been exposed to any of the following against your will?”. Included in the options were: someone having exposed him-/herself to you via the Internet or otherwise, someone having touched your genitals/tried to undress you to have sex with you, forced you to masturbate or have vaginal, oral or anal intercourse. Flashing is by definition an abusive act according to Swedish law if it is against the will of the victim, irrespective of whether it occurs in real life or via the Internet, which is why it was included in the analysis for being exposed to ‘any sexual abuse’. Further analyses were made, including only penetrative abuse (oral/anal/vaginal abuse). Follow-up questions for sexual abuse were asked concerning the first exposure, as follows; age of the victim, relationship to the perpetrator and type of sexual abuse. One question was asked concerning the total number of times exposed to sexual abuse. All questions concerning sexual abuse were used in the questionnaires from 2004 and 2009.
Exposure to emotional and physical abuse was measured by the question; “Have you prior to the age of 18 been subjected to any of the following by an adult?”. Emotional abuse was measured through three questions; insulted, threatened to be hit, isolated from friends. Physical abuse was measured by eight questions, ranging from being pushed or shaken, hit with the hands or items, burned or strangled. The answers were ranked into four; never—rarely—sometimes—often. However, when analyzing the question the answers were dichotomized into ‘been exposed’ including the answers rarely, sometimes and often, or ‘never been exposed’. This instrument has not been validated but has been used in the earlier studies from 2004 and 2009.
Contact with healthcare for psychiatric disorders was measured with the question: “Have you ever been in contact with healthcare services for…” giving the following options: Depression/anxiety, Eating disorders, ADHD/ADD or similar, Autism/Asperger, Suicide attempt, Alcohol/Drug abuse. This question was new and formulated for this survey. The occurrence of NSSI was investigated with a general screening question: “Have you ever done something to purposely hurt yourself without intending to die?” This is a question included in the structural interview Self-Injurious Thoughts and Behaviors Interview—SITIB .
Trauma symptoms were measured by Trauma Symptom Checklist for Children (TSCC), an instrument designed to identify a broad range of trauma symptoms in children aged 8–17 years . This is a widely-used self-report instrument for measuring trauma symptoms among children and adolescents  that has been used for adolescents up to 19 years of age [34,35,36]. The instrument comprises 54 items, divided into six subscales; anxiety, depression, post-traumatic stress (PTS), dissociation, anger and sexual concerns. Answers are arranged in the scale of four options Never—Sometimes—Often—Almost all of the time. Cronbach’s alpha coefficient for the subscales has been assessed to be .77 to .89 and .84 for the entire instrument . There is a Swedish translation and validation for the 10–17 age group, giving a Cronbach’s alpha coefficient for the total scale of .94 with the variation of .78 to .83 for the subscales . In the present study the Cronbach’s alpha was .95 for the total scale and .82 for anxiety, .88 for depression, .87 for PTS, .85 for dissociation, .84 for anger and .65 for sexual concerns.
Categorical data was presented using frequencies and cross tabulation and analyzed with Chi square test and Fisher’s Exact test using p value <.05. When comparing means such as age and TSCC, t test for independent groups was used. Percentages presented in the study relate to the number of adolescents answering the question. Missing answers in individual questions were at most 9.7%. Analyses by gender boy/girl were made but since the number of boys was very small, few statistically significant differences were found, indicating an increased risk of type II errors. Results are therefore presented divided by gender boy/girl only when statistical significance with a p value <.05 was seen. In the analyses the answer alternatives concerning living situation were merged from seven to four alternatives (living with both parents or alternating/living with one parent with or without new partner/alone or with siblings or partner/in foster care or institution), financial situation in the family from five to three alternatives (good/poor/do not know), sexual orientation from six to four alternatives (heterosexual/homosexual/bisexual/other or unsure), number of sexual partners from four to three alternatives (one, two to five and more than five). The questions concerning abortion and treatment for chlamydia were dichotomized from four to two alternatives (yes/no) and the question concerning total number of times exposed to sexual abuse was dichotomized from three to two alternatives (exposed one time/exposed more than one time). To make a model with the most important factors associated to SASI, forward stepwise binary logistic regression was performed with SASI as a dependent variable and sex, financial situation in the family, heterosexual sexual orientation, selling sex, all kinds of sexual abuse, penetrative abuse, emotional and physical abuse, trauma symptoms, healthcare for psychiatric disorders and NSSI, as covariates. All statistical analyses were carried out in Statistical Package of the Social Sciences (SPSS) version 22.