Selectivity processes in and weights for the Berlin Aging Study II (BASE-II)

Like many medical studies, the Berlin Aging Study II (BASE-II) is based on a non-random "convenience sample" of self-recruited participants. To study processes of selectivity in BASE-II, we used an identical questionnaire to compare BASE-II with a large, representative reference study, the German Socio-Economic Panel (SOEP), thereby allowing differences in characteristics of participants in BASE-II and SOEP to be analysed easily. Based on this selectivity analysis, we then generated propensity score weights that adjust for the selectivity in the BASE-II survey. In addition, we adjusted the weights of the BASE-II sample to regional information from the Federal Statistical Office so that the BASE-II study has the same totals as the official statistics.