Target Population and Samples¶
The target population covered in the SOEP is defined as the residential population living in private households within the current boundaries of the Federal Republic of Germany (FRG). Because of changes in these boundaries (in 1990) and changes in the residential population due to migration, various adaptations have been applied to the initial sampling structure to keep the sample’s representativity. In addition, certain groups have been oversampled to increase the statistical power. In 1984, the survey started with a sample covering the entire population in then West Germany (FRG), where the five biggest groups of foreigners (the so-called “guest-workers”) were oversampled.
The institutionalized population, in the true sense of the word (hospitals, nursing homes, military installations) is generally not representatively included in new samples. E.g. in 1984 only 57 institutionalized households are included. Later, however, persons from the initial households who have taken up residence temporarily or permanently in institutions of this kind are followed.
The SOEP was expanded to the territory of the German Democratic Republic in June 1990, only six months after the fall of the Berlin Wall. A further addition in 1994/95 was a sample of migrants who came to Germany after 1984, to take the influx of ethnic Germans from former Soviet countries into account. Two samples representative of the entire population in Germany were added in 1998 and 2000, to counter effects of panel attrition and to increase the overall sample size. In 2002, a high income sample was added, while in 2006 and 2009, additional refreshment samples were drawn.
To increase the overall sample size SOEP has started adding refreshment samples in 2011. While the first (in 2011) and second (2012) extensions are representative of the whole population, the third (2013) is supposed to explicitly cover migrants. For the fourth extension in 2014, the related study “Families in Germany”, covering mainly families, will be integrated into the SOEP.
The different samples in the SOEP are identified by letters: sample “A” refers to the German sample drawn in 1984, “C” to the East Germans from 1990, and so on. Even though these samples are kept separate, the respondents received identical questionnaires for the most part and distinctions by sample are usually not be necessary in an analysis. However, one of the ideas of SOEP is, that the users have full information available about survey methodological issues and survey design. Which means in this case that you can of course identify the corresponding sample for each observation. In the following section, we present details on each of the samples, which - unless stated otherwise - are multi-stage random samples with regional clusters. The respondent’s households are selected by random-walk routines.
For an extensive discussion on sampling (and weighting): Survey methods.