Cohort Change

The concept of cohort change, which is an attempt to link the "biological rhythm of human existence" (Mannheim, 1952) with the "evolution of the social order" (Parsons, 1951), is a prime example of a tool designed to analyze linkages between the micro (i.e., individual) and macro (i.e., societal) levels of human reality. The phenomena of cohort replacement creates opportunities for societies to rethink, and perhaps redefine, individuals' roles, rights, responsibilities, and rewards. This connection between changes in culture and the gradual and continuous processes of individual aging, birth, and death has led sociologists to investigate how these demographic processes may intersect with personality development.

Although cohorts can be defined in a variety of ways (e.g., a new cohort of graduate students, a new cohort of employees), questions of cohort change, cohort replacement, and cohort succession are primarily about birth cohorts—people born within a given time period. Ryder (1965) described the process of cohort change as an illustration of "demographic metabolism." Social change and population processes are interdependent because the composition of society (aggregate characteristics of the set of individual members) is always in flux. Fertility and in-migration infuse a society with new members, while mortality and out-migration deplete a society of its members. The continuing change in a society's membership creates a dynamic at the macro level that is different from the micro-level dynamic of individual aging. Aging as an individual, biological process also has social implications, because as people age they move from one set of roles or positions to another. In addition, aging is connected to population dynamics through fertility, mortality, and in- and out-migration. Therefore individual aging creates connections between the pace of demographic change and societal transformation. Cohort continuity through the life span provides the element of stability, whereas the perpetual entry, aging, and exit of successive cohorts provide flexibility.

Although initially framed as "the problem of generations" (Mannheim, 1952), the issue under consideration was essentially that of cohort succession—the entry, aging, and exit of successive cohorts—and how it is linked to social change. In 1965, Norman Ryder formulated one answer to this question by describing how cohort characteristics (e.g., size, race/ethnic composition, average level of education) could provide the impetus for social change. The impetus for social change in his demographic approach concentrated on an easily observable feature, the equilibration of supply and demand. For example, an unusually large cohort (e.g., the baby-boom cohort) would require building more schools, hiring more teachers, and perhaps the development of community activities for children. In contrast, an unusually small cohort might motivate an emphasis on small classroom size or changes in immigration policy. Although these stimulus-response pairings seem logical, they represent a subset of a much larger number of possible pairings. Why was the response to the baby boom a school construction program rather than a massive shift to home schooling? And if a small cohort cannot satisfy the demand for labor, why not change expectations and policies governing the average workweek, the frequency of vacations, and/or the child labor laws? These questions illuminate the heart of the puzzle. For it is not only the objective features of a cohort—by itself or relative to those of adjacent and/or coexisting cohorts—that determine the societal response to the demographic stimulus. Subjective factors are also important, for it is here that the link between the perceived importance of the stimulus and the appropriate response (e.g., relative to constraints, expectations) is forged.

That the biological process of aging is embedded in a social context creates variability in the experience of aging. This variability can be expressed as the difference between individuals, between cohorts, and over time. But it is not simply time (or historical location) that accounts for this variability, for shared experiences require a common framework of perception, interpretation, and reaction. The methodology of cohort analysis requires that people be classified into groups initially based on quantitative markers such as age, date of birth, date of marriage, or date of hire. Group boundaries are created relative to start dates and similar to any grouping exercise, boundary problems are encountered. If it is a birth-year cohort that is of interest, should that year run from January 1 through December 31, from September 1 through August 31, or some other start and end date? How is it sensible to assign two people born on consecutive dates to different cohorts?

While birth cohorts are often used to organize individuals, for analytic purposes the subjective experiences of cohort members must also be considered. The fact that each cohort is defined by a unique intersection of biography and history provides the possibility for commonality of subjective experience, but this potential is actualized only if the subjective experience of history is the same or similar across cohort members. Events must arouse the same kind of outrage or celebration; ideas must elicit similar levels of inspiration or aversion; public figures must be viewed with similar levels of admiration or revulsion.