Studies various aspects of psychological development during the adult years. Originally, in 1956, five hundred GHC members were randomly selected. They ranged in age from their early 20s to late 60s. The study has continued in seven-year intervals since 1956: 1963, 1970, 1977, 1984, 1991, 1998, and 2005. At each interval, all persons who had previously participated in the study were asked to participate again. In addition at each seven-year interval, a new group of people randomly selected from the Group Health membership have been asked to participate. Approximately 6000 people have now participated at some time in this study. Of the original participants, 26 people remain who have now been in the study for 50 years.