Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

AIM: Strong associations have been found between being exposed to self-harm in family and friends and own self-harm in adolescence. Therefore, self-harm and suicide behaviour might tend to cluster within school and school classes. The aim of this study was to describe the prevalence, frequency and type of self-harm, suicide ideation and suicide attempts within Danish high schools and to test whether self-harm and suicide behaviour cluster in schools and school classes. METHODS: Data came from the Danish National Youth Study 2014, a national survey. The respective study included 66,284 high-school students nested in 117 schools and 3146 school classes. The prevalence and clustering of self-harm behaviour, ever and within the last year, type of self-harm (e.g. cutting, burning, scratching and hitting) and suicide ideation and suicide attempts were investigated. Multi-level logistic regression was applied to quantify clustering among participants within the same class and school. RESULTS: In total, 12,960 (20%) reported self-harm ever and 5706 (8.6%) within the last year. Prevalence was higher among girls than boys. Among girls, cutting (15%) and scratching (13%) was the most common type of self-harm, whereas among boys, hitting (6.7%) was most prevalent. The degree of clustering of self-harm and suicide behaviour was low, with school-level intra-class correlation coefficients (ICC) ranging from 0.8-1.8% and school class level ICC's from 4.3-6.8%. CONCLUSIONS: This study shows that self-harm was common, especially in girls. The degree of clustering of self-harm and suicide behaviour in school and school classes was low.

Original publication




Journal article


Scand J Public Health

Publication Date





146 - 156


Clustering, school-level variation, self-harm, suicide attempt, suicide ideation, youth, Adolescent, Denmark, Educational Status, Female, Humans, Male, Prevalence, Risk Factors, Schools, Self-Injurious Behavior, Students, Suicidal Ideation, Suicide, Attempted, Surveys and Questionnaires