So-called proxy interviews are also permitted for data collection in the microcensus, that is, the microcensus contains both details about an individual that are self-supplied and details obtained by third-party interview. The type of participation in the microcensus, thus whether interviews provide self-supplied or third-party information, was first collected in 1999 in the context of the microcensus integrated into the EU labor force survey. This is earmarked and made available for the scientific community in Germany in scientific use files dating from 1999. For the microcensus dating from 1999, the share of proxy interviews for persons aged above 15 years was just over one quarter and corresponds to the average proxy shares of most EU Labor Force Surveys that are between 25 and 30 percent. However, substantially higher values can also be observed; indeed, for individual groups values are recorded of up to 80 percent. The share of proxy interviews for 15 to 19-year-olds in the 2005 microcensus is approximately 75 percent. Equally, the share is higher for immigrants/ethnic minorities or pupils in secondary schools.
The project examined the consequences of proxy data for the quality and precision of sampling results of the German microcensus. The following question was the central focus: How does the share of proxy information vary for different socio-cultural characteristics, and which characteristics influence the probability that proxy data is available for someone?