{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,4]],"date-time":"2026-05-04T23:37:04Z","timestamp":1777937824597,"version":"3.51.4"},"reference-count":35,"publisher":"SAGE Publications","issue":"2","license":[{"start":{"date-parts":[[2018,9,17]],"date-time":"2018-09-17T00:00:00Z","timestamp":1537142400000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.sagepub.com\/page\/policies\/text-and-data-mining-license"}],"content-domain":{"domain":["journals.sagepub.com"],"crossmark-restriction":true},"short-container-title":["Scand J Public Health"],"published-print":{"date-parts":[[2019,3]]},"abstract":"<jats:p>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\u20131.8% and school class level ICC\u2019s from 4.3\u20136.8%. 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.<\/jats:p>","DOI":"10.1177\/1403494818799873","type":"journal-article","created":{"date-parts":[[2018,9,17]],"date-time":"2018-09-17T13:53:26Z","timestamp":1537192406000},"page":"146-156","update-policy":"https:\/\/doi.org\/10.1177\/sage-journals-update-policy","source":"Crossref","is-referenced-by-count":15,"title":["School- and class-level variation in self-harm, suicide ideation and suicide attempts in Danish high schools"],"prefix":"10.1177","volume":"47","author":[{"given":"Veronica S.C.","family":"Pisinger","sequence":"first","affiliation":[{"name":"National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Keith","family":"Hawton","sequence":"additional","affiliation":[{"name":"Centre for Suicide Research, Department of Psychiatry, Oxford University and Oxford Health NHS Foundation Trust, 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