Time changes, so do people

► The author discusses age-period-cohort analyses by distinguishing the concept of time in terms of composition and context. ► Age is a composition of time, whereas both period and cohort can be conceptualized as a context of time. ► Age is a compositional variable, and a hypothetical intervention to change age is at the individual level. ► Two distinct types of hypothetical interventions can be envisaged to examine the contextual effects of period and cohort. ► Context is proposed to be classified into three fundamental dimensions - relational, spatial, and temporal.