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The German Twin Family Panel (TwinLife) is a German longitudinal study of monozygotic and dizygotic same-sex twin pairs and their families that was designed to investigate the development of social inequalities over the life course. The study covers an observation period from approximately 2014 to 2023. The target population of the sample are reared-together twins of four different age cohorts that were born in 2009/ 4). In the first wave, the study included data on 4097 twin families. Families were recruited in all parts of Germany so that the sample comprises the whole range of the educational, occupational and income structure. As of 2019, two face-to-face, at-home interviews and two telephone interviews have been conducted. Data from the first home and telephone interviews are already available free of charge as a scientific use-file from the GESIS data archive. This report aims to provide an overview of the study sample and design as well as constructs that are unique in TwinLife in comparison with previous twin studiessuch as an assessment of cognitive abilities or information based on the children's medical records and report cards. In addition, major findings based on the data already released are displayed, and future directions of the study are presented and discussed.

Internalizing and externalizing behavior problems are established risk factors for many unpleasant outcomes and psychopathology in adulthood, and understanding the interplay between genes and environment is important for deducing implications for therapeutic interventions. Among genetic studies on internalizing and externalizing problem behavior, the heritability estimates differ widely. Most research only uses twin data and other-reports, and therefore certain limitations are inevitable. Our study is the first to investigate genetic and environmental influences on problem behavior using a Nuclear Twin Family Design and self-reports, in order to address these limitations. Internalizing and externalizing problem behavior of 3,087 twin pairs (age 11-23), a sibling, and their parents were analyzed with structural equation modeling to estimate heritability separately for each of three twin birth cohorts. Genetic influences account for about one-third of the variance for both internalizing and externalizing. Shared environmental influences were only found for internalizing, and through the advantages of considering data from the whole twin family, firstly could be identified as solely twin-specific. Our findings could contribute to a better understanding of the gap between heritability based on twin studies and DNA-based heritability ('missing heritability problem'): Results indicate that heritability estimates gained via classic twin design and other-reports are slightly overestimated and therefore environmental influences, in general, are more important than previous research suggests. Simultaneously, we showed that family-specific environment either contributes to behavior problems only on an individual level, or that it has a lesser influence than originally thought.

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Zusammenfassung. Mit dem Fragebogeninventar für Freizeitinteressen (FIFI; Piepenburg & Kandler, 2016 ) steht nun erstmals ein deutschsprachiges Messinstrument für das Erwachsenenalter zur Verfügung, welches Freizeittätigkeiten hinsichtlich ihrer intrinsischen Wertigkeit (Freizeitinteresse) und Häufigkeit ihrer Ausübung (Freizeitaktivität) erfasst. Ziel der vorliegenden Arbeit war die Entwicklung einer Kurzversion (FIFI-K), um die Ökonomie der Erfassung bei gleichbleibender Heterogenität der Freizeitbereiche zu erhöhen. Das FIFI-K umfasst 67 Items, an denen die Struktur von Freizeitinteressenbereichen (21 Primärfaktoren und 5 Sekundärfaktoren) des FIFI bei 840 Probandinnen und Probanden mittels konfirmatorischer Faktorenanalysen bestätigt werden konnte. Basierend auf einer Substichprobe von 443 Probandinnen und Probanden fanden sich gute Retest-Reliabilitäten für entsprechende Freizeitbereiche. Zudem konnten konvergente Validität zwischen Freizeitinteresse und Freizeitaktivität und diskriminante Validität zwischen den Freizeitbereichen sowie prädiktive Validität von Freizeitinteressen und -aktivitäten zur Vorhersage psychischen Wohlbefindens bescheinigt werden. Das FIFI-K kann demnach als ökonomisches, reliables und valides Messinstrument für die individuelle Erfassung von Freizeitinteressen und -aktivitäten in Forschung und Praxis angewandt werden.