Funding for this research was provided by:
Deutsche Forschungsgemeinschaft (610/6-1)
Received: 11 December 2017
Accepted: 8 November 2018
First Online: 29 November 2018
Compliance with ethical standards
: Wendy Johnson, Elisabeth Hahn, Juliana Gottschling, Franziska Lenau, Frank M. Spinath, and Matt McGue declare that they have no conflicts of interest.
: TwinLife received ethical approval from the German Research Foundation. MTFS received ethical approval from the University of Minnesota Institutional Review Board.
: Adult participants gave fully informed consent for themselves and their underage participating children, and participating underage children gave fully informed assent.