The K²ID sample is based on all households with children born on 1 September 2007 or later that participated in the 2013 wave of SOEP or FiD and did not refuse survey participation for 2014 from the outset. Therefore, at the beginning of field work in October 2013, target children were between zero and six years of age.
The German Socio-Economic Panel (SOEP) is a representative longitudinal survey of private households and persons in the Federal Republic of Germany that was started in 1984 (Wagner et al. 2007). In 2012, 21,050 persons from 12,322 households participated in the study. It consists of numerous subsamples that either existed from the beginning or were added during the course of the study. Within the SOEP, 18 samples are included. In 2013, for the third time in the history of the SOEP, a subsample was added that is composed exclusively of migrant households. SOEP sample M represents younger generations of migrants, including immigrants since 1995 and second generation migrants, which were underrepresented for the decade before. Due to the recent addition of sample M, all field work related to K²ID was postponed by one year (see ‘documentation’ for details on the timing of data collection).
Since 1984, the SOEP has been augmented by several supplementary studies, among others by the ‘Families in Germany’ Study (FiD; in German: ‘Familien in Deutschland’). FiD is a dataset on families with young or numerous children, a single parent or low household income, which were surveyed for the first time in 2010 (Schröder et al. 2013). The FiD data contain information from about 4,500 households with a total of 7,500 respondents and over 8000 children. In 2014, the FiD sample was integrated into the SOEP. It consists of seven subsamples, four of which are representative cohort samples defined by the birth year of one child in the family, ranging from 2007 to 2010. For the remaining subsamples representing households with single parents, low income, and families with three or more children, sampling was conducted using a screening process. The composition of the K²ID sample including the size of all subsamples is illustrated in the figure above.
Overall, the gross sample amounts to 3,065 households with 3,916 children originating from SOEP and FiD. All households were asked to complete the Parent Survey for each child falling in the required age range. Among other things, the questionnaire served to gather the address of ECEC institutions used by the surveyed households. Almost three in four households took part in the survey, and for about 93 percent of children attending ECEC institutions, parents reported the institution's address. This resulted in a gross sample of 1,528 ECEC institutions whose staff was subsequently invited to participate in the ECEC Institution Survey. Ultimately, information on a total of 989 ECEC groups in 854 ECEC institutions was collected, equating to a response rate of about 56 percent.
Wagner, G. G., Frick, J. R., & Schupp, J. (2007). The German Socio-Economic Panel Study (SOEP) — Scope, evolution and enhancements. Schmollers Jahrbuch, 127, 139–169.
Schröder, M., Siegers, R., & Spieß, C. K. (2013). “Familien in Deutschland” — FiD. Schmollers Jahrbuch/Journal of Applied Social Science Studies, 133, 595–606.
For further information on SOEP and FiD, please consult: