Development of Sample Sizes¶
Individuals who refuse participation or are not available for an interview are kept in the so-called “gross” sample of the study as long as they continue to live in households with at least one participating person. Once the entire household declines to respond in two consecutive waves of data collection, all individuals from the household are removed from the SOEP. The table shows the starting sample sizes of samples A through N, the years when the samples were first collected, as well as the percentage of those persons who were eligible for an interview but declined participation (“partial unit non-response”, PUNR) in the first wave. The figure illustrates the development of the number of successful person interviews since 1984. The reduction in the population size for all individual samples is mainly the result of person-level drop-outs, refusals, moving abroad, etc. However, due to new persons moving into already existing households, and children reaching the minimum respondent’s age of 16, and thereby increasing the sample size, this negative development is offset somewhat.
Starting Sample Size of the SOEP Samples
Cross-Sectional Development of Sample Size (Respondents)
This cross-sectional view is insufficient when examining the longitudinal development of the sample, which is influenced by different demographic and field-work related factors. As already shown, demographic reasons for entering the panel are birth and residential mobility. Analogously, the demographic reasons for a panel exit are death and moving abroad. Fieldwork related reasons are different, in that they relate to the interaction between the interviewer and the responding household. Respondents are either not reached for an interview (non-contact) or they decline to participate for the current year. The figure illustrates the longitudinal development of first-wave respondents in 1984, as well as their children, of samples A and B.
Longitudinal Development of the 1984 Population