The phenotypic data were obtained in the longitudinal surveys on lifestyle, health, and personality of the NTR (e.g., Boomsma et al. 2002, 2006). The study protocols were approved by the Central Ethics Committee on Research Involving Human Subjects of the VU University Medical Center, Amsterdam. All participants provided informed consent. The study in young twins was approved also by the Central Committee on Research Involving Human Subjects. More details regarding the phenotyping in the NTR study can be found elsewhere (van Beijsterveldt et al. 2013; Willemsen et al. 2013).
