Access to high-quality, population-based person-linked registers has enabled major contributions to psychiatric epidemiology. For example, researchers have documented key risk factors within psychiatric epidemiology, for example, urban birth,50, 51, 52, 53, 54 paternal age,55, 56, 57 psychiatric family history,58, 59 life-time risk,60 infections,17, 19, 20 neonatal vitamin D deficiency,61 socio-economic adversity,62 treatment resistant schizophrenia,63 pharmacological treatment,64 suicide65 and excess mortality.66 Key features such as the avoidance of selection bias and control of multiple confounders have been important aspects of these studies. However, genetic studies have traditionally not had access to population-based samples, with cases often recruited from multiplex families, or convenient samples of prevalent cases in contact with mental health services. The iPSYCH2012 sample includes a large representative sample of severe mental disorders from a representative sampling frame. The possibility to link the iPSYCH2012 sample to the comprehensive and high quality Danish population-based registers offers researchers unique possibilities to study the interplay between the genetic factors, and variables from the environment, and variables related to health,27, 67, 68, 69 mortality, income and social and socioeconomic characteristics.70, 71, 72 Genetic association
