Delayed Sleep Phase Syndrome in Adolescents: Prevalence and Correlates in a Large Population Based Study Børge Sivertsen, Ståle Pallesen, Kjell Morten Stormark, Tormod Bøe, Astri J. Lundervold, Mari Hysing January 2013 Cite DOI epidemiology public health biostatistics environmental health general medicine/public health vaccine ⛔ no doi found Related The Strengths and Difficulties Questionnaire (SDQ): Factor Structure and Gender Equivalence in Norwegian Adolescents