The two questionnaires for ECEC institutions were developed in September and October 2013 as part of the SOEP-K²ID project (see Schober et al. 2017). The center addresses were available in the end of 2014 and checked, Kantar Public (formerly TNS Infratest) started the first phase of field work lasting from March to December 2015 and the second field phase lasting from January to September 2016. The questionnaires were sent to the directors of all ECEC institutions and to an educator of each group serving a TwinLife child, preferably the educator bearing the main responsibility for the class.
Timeline of data collection for K²ID-Twins