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 studies are by default observational studies, subject to many of the same sources of bias and confounding as other epidemiological studies.16 Therefore, we believe our samples can assist the assessment of the potential impact of such biases and especially lack thereof, and point toward new avenues of research. For example, it has been shown that the genetic associations with schizophrenia identified in the seminal Psychiatric Genomics Consortium paper3 were stronger in more chronic cases than in first episode cases.73 This may suggest that, in future studies, the genetic architecture of schizophrenia could perhaps be refined to identify genes particularly associated with the risk of developing disease, and genes particularly predicting a chronic course, something that could have important preventive and clinical implications. Such future studies will benefit from the continued dialogue between epidemiological studies as iPSYCH and the large-scale studies available only through collaboration in international consortia.
