Two-wave longitudinal findings from the Berlin aging study: introduction to a collection of articles.

We provide background information for a collection of articles that describe two-wave longitudinal findings derived from the first intensive follow-up of participants of the Berlin Aging Study (BASE). Multidisciplinary data were collected during 1995-1996 from 206 survivors approximately 4 years after baseline assessment (1990-1993). The strengths of the initial BASE design, in terms of a focus on very old age, multidisciplinary intensive assessment, and an examination of selectivity issues, were maintained in this longitudinal extension of the study.