Gauging effects of historical differences on aging trajectories: The increasing importance of friendships.

For a long time, life span psychologists have theorized that individual development is partially shaped by an everchanging historical context. For example, it has been hypothesized that the historically increasing flexibility of constructing social networks may influence the social development of adults into late life. To date, however, there is no established method in psychological science that allows researchers to easily gauge the effects of historical differences in time-varying covariates on aging trajectories, which are also subject to historical change. Here, the method of cohort centering is introduced as a potential remedy for this dilemma. Using a large-scale, cohort-sequential data set, representative of the German population aged 40 to 85 years (N = 19,017), I applied cohort centering to examine historical differences in the aging trajectories of number of friends in the close personal networks and time spent in activities with friends. The results indicated that older cohorts may be more engaged with friends than younger cohorts. Results also showed that historical differences in friendship relations in later life could partially be explained by historical gains in self-rated health, education, and individual perceptions of aging. In sum, cohort centering can tell us how future aging trajectories will look given a specific set of preconditions and can provide information about what could happen if these conditions change. (PsycINFO Database Record (c) 2019 APA, all rights reserved).