I agree with Costanza and Finkelstein (Reference Costanza and Finkelstein2015) that it is futile to further invest in the study of generational differences in the work context due to a lack of appropriate theory and methods. The key problem with the generations concept is that splitting continuous variables such as age or time into a few discrete units involves arbitrary cutoffs and atheoretical groupings of individuals (e.g., stating that all people born between the early 1960s and early 1980s belong to Generation X). As noted by methodologists, this procedure leads to a loss of information about individuals and reduced statistical power (MacCallum, Zhang, Preacher, & Rucker, Reference MacCallum, Zhang, Preacher and Rucker2002). Due to these conceptual and methodological limitations, I regard it as very difficult if not impossible to develop a “comprehensive theory of generations” (Costanza & Finkelstein, p. 20) and to rigorously examine generational differences at work in empirical studies.

I do believe however that studying generations based on social identity and stereotyping perspectives is interesting and important in the work context because, as noted by Costanza and Finkelstein, “people believe that they exist” (p. 21). Indeed, organizational researchers have argued in several recent review articles that people's beliefs about generational differences are not based on actual differences but are socially constructed, mainly by relying on knowledge about common age and generation stereotypes (Joshi, Dencker, & Franz, Reference Joshi, Dencker and Franz2011; Joshi, Dencker, Franz, & Martocchio, Reference Joshi, Dencker, Franz and Martocchio2010; Lyons & Kuron, Reference Lyons and Kuron2014; Rudolph & Zacher, Reference Rudolph, Zacher, Finkelstein, Truxillo, Fraccaroli and Kanfer2015). Moreover, research in the field of lifespan developmental psychology has shown that identifying with a generational group, as opposed to an age group, can have positive implications for older adults’ self-concept and well-being (Weiss, Reference Weiss2014; Weiss & Lang, Reference Weiss and Lang2009). This research suggests that interventions addressing generational identities and stereotypes may be useful for managers and employees even if no actual differences exist between generations in the work context.

If the theoretical and empirical investigation of generational differences is discontinued, which alternative approach could researchers use to examine potential age- and birth cohort-related differences and changes over time in outcomes such as work-related attitudes, values, and behavior? (Note that I use the term cohorts here to refer to individuals’ birth years and not their generational membership, which involves forming broader categories of individuals based on their birth years and shared life experiences). The goal of this commentary is to expand on Costanza and Finkelstein's limited directions for future research by recommending the use of lifespan developmental theory and methods as a viable alternative to the study of generations in the work context (see also Zacher, Reference Zacher2015).

According to lifespan developmental theory, there are three broad categories of influences on development that individuals have to process, react to, and act on (Baltes, Reference Baltes1987). These three influences differ from the three factors briefly mentioned in Costanza and Finkelstein's focal article (i.e., age, historical period, and generational cohort, with the former two being used to create the third). First, normative age-graded influences entail determinants of development that are encountered by most people as they age, such as biological maturation (e.g., decline in physical strength and fast information processing abilities) and very common socialization events (e.g., school entry, marriage, birth of children, retirement). It is important to note that there are interindividual differences in these normative age-graded influences. Second, history-graded influences refer to determinants linked to the historical period in which individuals develop (Baltes, Reference Baltes1987). For instance, the fall of the Berlin wall influenced the life courses of people living in East Germany in the 1990s to different extents. History-graded influences differ from the generations concept as they do not involve categorizing individuals based on their birth years and shared life experiences. Instead, the lifespan developmental perspective suggests that events and experiences associated with a historical period constitute factors that can potentially impact on each individual's developmental outcomes. In contrast to assumptions of generations researchers, history-graded influences are not generally restricted to young people; however, age may act as a moderator. Lifespan developmental researchers do not use the generations concept to study age-related differences between groups of individuals; when they did use the term, they were referring to individuals’ birth cohorts (Baltes, Reference Baltes1968). Finally, the third category involves nonnormative influences on development (Baltes, Reference Baltes1987), whose manifestation is unique to each individual. These idiosyncratic influences include severe illnesses, accidents, loss of a partner or close relative, or job loss. In sum, the three categories of influences on development from lifespan developmental theory provide organizational researchers with a more sophisticated theoretical framework to study potential age-related or birth cohort-related differences or changes over time in work outcomes than extant research on generations does.

Research in the field of lifespan developmental psychology has provided evidence for the effects of age- and history-graded influences on developmental outcomes. For instance, research on adult intellectual development found that fluid intelligence (e.g., memory, fast information processing), on average, decreases with age; at the same time, there are substantial improvements in fluid intelligence across successive birth cohorts (Gerstorf, Ram, Hoppmann, Willis, & Schaie, Reference Gerstorf, Ram, Hoppmann, Willis and Schaie2011; Schaie, Reference Schaie2013). Although this research demonstrated that intellectual development is influenced by the historical context, Baltes (Reference Baltes1987) already acknowledged that “classical psychological theory has little to offer when it comes to interpreting the substantive meaning and origin of cohort effects. . . . The fields of cultural anthropology, historical sociology, and historical medicine may prove to be more relevant” (p. 620). He suggested that likely explanations for cohort effects on intellectual development involve continuous improvements in education, health, and work environments (Baltes, Reference Baltes1987). In the work context, the theoretical relevance of history-graded birth cohort influences for work-related outcomes may be a factor that determines the strength of potential effects. For instance, experiencing a war is more likely to influence the development of individuals’ (not generations’) attitudes toward war than it is to influence their job satisfaction. In contrast, individuals’ (again, not generations’) attitudes toward job security may be influenced by the extent to which jobs were available when these people entered the labor market. Overall, lifespan developmental research suggests that history-graded birth cohort effects on individuals’ developmental outcomes can exist, whereas this line of research does not make assumptions about broader effects on collective attitudes, values, and behaviors of generational groups.

In terms of methods, the lifespan developmental literature offers a rich toolbox to study aging, birth cohort, and idiosyncratic influences on developmental outcomes (Baltes, Reference Baltes1968; Hofer & Sliwinski, Reference Hofer, Sliwinski, Birren and Schaie2006). As noted by Costanza and Finkelstein, cross-sectional designs, which are frequently used to study generational differences, cannot disentangle aging from cohort and selection (or mortality) effects (longitudinal studies cannot achieve this as well). Several conditions have to be met for cross-sectional findings to be theoretically consistent with assumptions on either aging or cohort effects (Zacher, Reference Zacher2015). An important methodological alternative that is widely discussed in the lifespan development literature is the cohort-sequential design, which is the only design that can effectively disentangle different influences on developmental outcomes. This comparative research design involves assessing individuals from multiple birth cohorts as they age (i.e., across several decades). Unfortunately, the cohort-sequential design has not been used (yet) in research on work and aging due to its high costs and time investments (Ng & Feldman, Reference Ng and Feldman2008). However, there is no alternative to this approach if we want to gain a better understanding of aging and birth cohort effects on work outcomes.