Encyclopedia of SociologyVol._3

such as the age of young adulthood, or to analytically defined positions, such as the career stage of men or women at age forty (i.e., where they are in their career at this age). Thus, men who differ in age when they encounter work-life misfortune occupy different life stages at the time.

Developmental stages and trajectories are the focus of life-span developmental psychology. Examples of a stage theory include Erik Erikson’s (1963) psychosocial stages, such as the stage of generativity in the later years. Life-span developmental psychology gained coherence and visibility through a series of conferences at the University of West Virginia beginning in the late 1960s (Baltes and Reese 1984). The approach is defined by a concern with the description and explanation of age-related biological and behavioral changes from birth to death.

All the above concepts have a place in studies of the life course. Contemporary inquiry extends across the life span and frequently draws upon the life records and life cycles of successive generations. The life course takes the form of a multidimensional and intergenerational concept: a dynamic life pattern of interlocking trajectories and transitions, such as work, marriage, and being parents. Within this context, misfortune and opportunities are intergenerational as well as personal life events. Failed marriages and work lives can lead adult offspring back to the parental household and alter the parents’s life plans for their later years (Goldscheider and Goldscheider 1993). Conversely, parents’ economic setbacks and marital dissolution may impede their children’s transition to adulthood by postponing higher education and marriage. Each generation is bound to fateful decisions and events in the other’s life course.

THE EMERGENCE OF LIFE-COURSE

THEORY

When pioneering investigators followed children born before 1930 into their adult years, they encountered major limitations in conventional approaches to human development, including those associated with a child-based model. Three such limitations and their challenges, in particular, played a major role in the genesis of life course theory and appropriate methods (Elder 1998):

1.To formulate concepts that apply to development and aging across the life span as a replacement for child-based, growth-oriented accounts.

2.To conceptualize how human lives are socially organized and evolve over time.

3.To relate lives to an ever-changing society, with emphasis on the linking processes and mechanisms and the developmental effects of changing circumstances.

Responses to the first challenge in the 1970s led to the formulation of more life-span concepts of development and aging (Baltes and Baltes, 1990; Baltes et al. 1998), especially with the field of lifespan developmental psychology. Life-span development is conceived as a life-long adaptational process. Some processes are discontinuous and innovative, while others are continuous and cumulative. Biological resources tend to decline over the life span, whereas cultural resources may increase, as in the growth of wisdom. Theorists stress the lifelong interaction of person and social context, the relative plasticity and agency of the aging organism, and the multidirectionality of life-span development (Lerner 1991). Psychologist Paul Baltes at the Berlin Max Planck Institute is a leading figure in the programmatic effort to study development and aging across the life span.

This emergence of life-span thinking on human development and aging occurred with little attention to a well-established ‘‘relationship’’ view of human lives. Dating back to the nineteenth century, social scientists have viewed the individual’s life pattern in terms of multiple role sequences and their transitions (Cain 1964; Kertzer and Keith 1984). Changes in social roles, such as from dependency to marriage and parenthood, represent changes in social stage across the life cycle. Commitments to a line of action arise from obligations to significant others. Stable relationships ensure a measure of personal stability, just as entry into such relationships can stabilize a person’s life and minimize involvement in unconventional and illegal activities (Robins 1966). A change in relationships may produce a turning point, a redirection of the life course.

Life-cycle theory helped to contextualize people’s lives by emphasizing the social dynamic of ‘‘linked lives.’’ These connections extend across the generations and across people’s lives through

convoys of friends and relatives—others who remain part of their social network as they age (Kahn and Antonucci 1980). One of the earliest proponents of a life-cycle view of lives was sociologist William I. Thomas. With Florian Znaniecki, he used life-record data to study the emigration of Polish peasants to European and American cities around the turn of the century (1918–1920). The societies they left and entered presented contrasting ‘‘lines of genesis’’ or role sequences for individual lives.

For many decades, the life cycle perspective offered a valuable way of thinking about the social patterning of lives, though insensitive to age, time, and historical context. During the 1960s, the lifecycle approach began to converge with new understandings of age to draw upon the virtues of each tradition; of linked lives across the life span and generations, and of temporality through an agegraded sequence of events and social roles, embedded in a changing world. The emerging theory of the life course was informed as well by life-span concepts of human development.

Three discoveries of variation in lives were based on this new understanding of age, and together they gave rise to life-course thinking. First, studies in the 1960s began to identify substantial variation in age patterns across lives: Contrary to established views (Eisenstadt 1956), people of the same age varied in the pace and sequencing of transitions in their lives. During the late 1950s and early 1960s, Bernice Neugarten (1968) developed a research program that featured normative timetables and individual deviations from such expectations. Ever since this pioneering work and the growth of social demography, the study of differential timing and order among events has been one of the most active domains in life-course study. However, we still know little about age expectations in large populations.

Second, social relations and kinship especially emerged as a primary source of variation and regulation of life trajectories. Lives are lived interdependently among members of family and kin. The most significant integration of age and relationship distinctions is found in Of Human Bonding (Rossi and Rossi 1990). Using a threegeneration sample in the Boston region, the study investigates the interlocking nature of the life

course within family systems, with particular focus on the relationship beween individual aging and kin-defined relationships across the life span.

Third, the new work on aging made visible the role of historical variation as a source of life variations. Studies of social change and life patterns had been conducted up to the 1960s as if they had little in common, an assumption effectively challenged by Norman Ryder’s concept of the interaction of individual lives and history (1965). Ryder proposed the term ‘‘cohort’’ as a concept for studying the life course—the age at which the person enters the system. With its life-stage principle, Ryder’s essay provided a useful point of departure for understanding the interaction between social change and the life patterns of birth cohorts. The impact of a historical event on the life course reflects the life or career stage at which the change was experienced. The publication of Aging and Society (Riley et al. 1972) strengthened this sensitivity to the historical setting of lives through membership in a particular birth cohort.

The three streams of life-course theory (social relations–life cycle, age, and life-span concepts of development) came together in a study of children who were born in the early 1920s, grew up in the Great Depression, and then entered service roles in World War II. In Children of the Great Depression

(Elder, [1974] 1999), the study began with ideas from the relationship tradition, such as generation and social roles, and soon turned to the analytic meanings of age for ways of linking family and individual experience to historical change, and for identifying trajectories across the life course. The study tested Ryder’s life-stage principle by comparing the effects of drastic income loss during the Great Depression on the family and individual experience of the Oakland study members with that of a younger cohort born toward the end of the 1920s (Elder et al. 1984). Consistent with the life-stage hypothesis, the younger boys in particular were more adversely influenced by family hardship, when compared to the older boys. But similar effects were not observed among the girls.

By the 1990s, the life course had become a general theoretical framework for the study of lives, human development, and aging in a changing society. This advance is coupled with the continued growth of longitudinal studies and the

emergence of new methodologies for the collection and analysis of life history data (Giele and Elder 1998; Mayer and Tuma 1990).

PARADIGMATIC PRINCIPLES

Life course theory is organized around paradigmatic principles that guide inquiry on issues of problem identification, model formulation, and research design. Four principles are primary: 1) the interplay of human lives and development with changing times and places; 2) the social timing of lives; 3) the interdependence of lives; and 4) human agency in choice-making and actions (Elder 1998).

1.The life course of individuals is embedded in and shaped by the historical times and places they experience over their lifetime.

When societies are undergoing rapid change, different birth years expose individuals to historical worlds with different opportunity systems, cultures, and structural constraints. Historical influences on life trajectories take the form of a cohort effect when social change differentiates the life course of successive cohorts, such as older and younger men before the World War II. History also takes the form of a period effect when the impact of social change is relatively uniform across successive birth cohorts. Birth year and cohort membership locate people in relation to historical change, such as the economic recession of 1982–83, but they do not indicate actual exposure to the change or the process by which historical influences are expressed. Direct study of such change and its influences is essential for identifying explanatory mechanisms.

Life stage informs such mechanisms; people of unlike age and those who occupy different roles are differentially exposed to and influenced by particular types of social change. Four other components of an explanatory mechanism (for linking social change to lives) are worth noting (Elder 1998, pp. 959–61). One linking factor is defined by social imperatives, the behavioral demands or requirements of new situations. The more

demanding the situation, the more individual behavior is constrained to meet role expectations. Studies of worklives by Kohn and Schooler (1983) suggest that the establishment of a new set of occupational and workplace imperatives can alter how workers think and function. A second factor involves the dynamics of a control cycle. A loss of personal control occurs when people enter a new world and this sets in motion efforts to regain this control. These efforts may entail new choices that construct a different direction in life, a different life course. Historical influences are often expressed through a network of relationships. Interdependent lives are thus a linking factor in the explanatory analysis. The last factor involves accentuation. When a social transition heightens a prominent attribute that people bring to the new role or situation, the process accentuates the effect of

the change. Our understanding of such change is enhanced by the principle of timing in lives.

2.The developmental impact of a life transition or event is contingent on when it occurs in a person’s life.

This principle subsumes the concept of life stage; social change affects the individual according to when the exposure occurred over the life course. Recruitment into the military illustrates this point (Sampson and Laub 1996). Mobilization immediately after high school occurs before marriage and worklife obligations, and during World War II, entry into the service at this time was less disruptive than it was for males who entered in their late twenties or thirties. Studies of veterans from World War II indicate that late entry into the armed forces significantly increased the risk of divorce, worklife disruption, and an accelerated pattern of physical health decline (Elder and Chan 1999). By comparison, early entry provided access to educational and job opportunities without the costs of life disruption.

Across the life course, Neugarten’s (1996) emphasis on the consequences of timing variations has been followed by

extensive research on differential timing patterns, from marriage and births to retirement (Shanahan in press). The impact of a life event, such as a personal loss, depends in part on when the event occurs. But to fully assess this impact, we must consider also the principle of linked lives.

3.Lives are lived interdependently and social and historical influences are expressed through this network of shared relationships.

Social relationships represent a vehicle for transmitting and amplifying the effects of stressful change, as in families under economic stress. For example, Depression hardship tended to increase the explosiveness of fathers who were inclined toward irritability before the crisis (Elder et al. 1986). And the more explosive they became under stress, the more adversely it affected the quality of marriage and effectiveness as a parent. Unstable family relations (marital, parent-child) became mutually reinforcing dynamics across the life course and generations. These dynamics tended to persist from one generation to the next through a process of individual continuity and intergenerational transmission.

Linked lives tend to transmit the life course implications of an ill-timed event in a person’s life. One of the clearest examples of this phenomenon comes from a study of female lineages in Los Angeles (Burton and Bengtson 1985). The birth of a child to the teenage daughter of a young mother created a large disparity be-

tween age and kinship status, between being young and facing the prospects of grandparental obligations. Four out of five mothers of young mothers actually refused to accept these new child-care obligations, shifting the burden up the generational ladder to the great-grandmother, who in many cases was carrying a heavy load. By comparison, the women who became grandmothers in their late forties or so were eager for the new role; in this lineage, a daughter’s timely transition to motherhood set in motion her mother’s timely transition to grandmotherhood. In

both cases, the principle of human agency addresses the process by which lives and life courses are socially constructed.

4.Individuals construct their own life course through the choices and actions they have taken within the constraints and opportunities of history and social circumstances.

Human agency has been a central theme in the study of biographies. Lives are influenced by social structures and cultures, but human agency can shape lives through the choices that are made under such conditions. In Clausen’s American Lives (1993), the central question is not how social systems made a difference in the life course, but why people made certain choices and thereby constructed their own life course. Clausen focused on the primary role of planful competence in late adolescence, that competent young people who think about the future with a sense of efficacy are more effective in making sound choices and in implementing them. This study found substantial support for this hypothesis in the lives of men in particular from adolescence to

the retirement age of 65. However, longitudinal research (Shanahan et al. 1997) shows that planful competence makes a difference only when opportunities are available. Planful competence was not expressed in education or occupational career among men who entered the labor market in the depressed 1930s.

The emergence of life course theory and methods can be viewed as a response to pressing questions in the 1960s. The rapidly developing field of human development and aging needed a conceptu-

al framework for thinking about the patterning of human lives in changing societies and its consequences. As life course theory addressed issue of this kind, it gained prominence as a theoretical orientation among fields of gerontology, criminology, social history, medical studies, developmental science, education, and social stratification. Noting such developments, Colby (Giele and Elder 1998, pp. x), refers to this approach as ‘‘one of the

most important achievements of social science in the second half of the 20th century.’’ Only time will tell about the accuracy of this appraisal. In the meantime, the field of life course studies continues to flourish.

REFERENCES

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GLEN H. ELDER, JR.

LIFE CYCLE

The life cycle is the socially defined, age-related sequence of stages individuals pass through beginning with birth and ending with death. Underlying the life cycle is the recognition that humans are biological organisms that are born, mature, and die. As with other biological organisms, reproduction is a key feature of human maturation, ensuring the persistence of the species.

FORMS OF THE LIFE CYCLE

In very simple societies, the life cycle may consist simply of two stages—infant and adult. Once infant survivorship is reasonably certain (typically by about age 6) young persons participate in adult work life, doing jobs that are suitable to their physical strength or as apprentices learning more complex skills. Work continues until death. But such a simple definition of the life cycle rarely endures the complexities attendant on reproduction. Among women, physical maturation separates childhood from the age when childbearing is possible. For men, marriage entails responsibility for supporting a family and guaranteeing their safety, something that typically must await completion of puberty and the achievement of economic viability. Even in societies with a low life expectancy, some adults survive to the point at which they are no longer able to work.

These examples illustrate how individual social roles (such as work or having a child) define a human life cycle that is more complex than the biological minimum. These roles are almost always defined as age related, and typically are also different for men and women. The concept of ageappropriate roles enables societies to regulate or prohibit behavior that is occurring ‘‘too early.’’ These societies also use the concept of age appropriateness to move individuals along in their maturation process, urging the adoption of a social role before it is ‘‘too late.’’

Age. In most societies, chronological age is a handy proxy for maturity, with particular age groups assigned certain responsibilities and rights. In some societies (such as in postwar Japan) the age appropriateness of the sequence of social roles is rigorously defined by cultural values and enforced by

social institutions (such as schools or labor markets) which impose strict age rules on entry, promotion, and exit. In African age-set societies the system is even more rigid: Groups of persons born during contiguous years are defined as members of a particular age group (age set). These age sets experience together the transition from one life cycle stage to the next, under community traditions that specify the formal requirements and ceremonies necessary to move from one set of social roles to another. Typically this process is one of considerable dispute—the moving up of one age set causes all members of the society to move to the next life-cycle stage so that one group will have to give up preferred adult roles for old age.

Age Stratification and Cohort Succession.

Individual childbearing and the aging of individuals ready to assume new age-appropriate roles drive the societal process of age stratification and cohort succession (Riley 1985). The more complex the society, the more social roles that need to be filled. Most such roles in the society are gender linked and age stratified (defined as age appropriate and differing markedly from age to age). The use of chronological age rather than maturational capacity to construct the age-stratification system mandates that individuals as they age will move from one age stratum to the next, with an implicit societal mandate of assuming new roles. The birth of persons in contiguous years (what demographers call a ‘‘birth cohort’’) reinforces the dynamic of the age-stratification system by producing new role entrants who can only be accommodated by the movement of all age strata to the next life-cycle stage. In the United States we can see this system at work in age-graded schooling: When one group achieves high school graduation, the remaining students are promoted from one grade to the next. This opens entry-level spaces for a new cohort to begin school. Universities develop a variety of incentives to get elderly faculty to retire so that newly trained and presumably more innovative faculty can be hired.

The Life Cycle in Social Science. To summarize, the lives of humans from birth to death are organized as socially defined, age-related sequence of stages individuals pass through over their lifetime. These stages are inherently age related, with individuals maturing from one life-cycle stage to the next. Reproduction is a key feature of human maturation, distinguishing the roles of men and

women and linked to the age-related biological capacity to bear children. An ongoing flow of new births ensures the persistence of human populations. Accommodating these new members of society also drives the dynamic of life-cycle change by necessitating the movement of earlier cohorts to more mature positions in the age-stratification system. This process of cohort succession is, in turn, a major source of societal innovation and change, as new cohorts take a fresh look at the content and form of the age strata they have just reached. In this way, the life-cycle concept links individual aging, the organization of roles in society, reproduction, and societal innovation and change.

CONTRIBUTIONS OF THE LIFE CYCLE

The life cycle has proved to be a powerful and flexible tool for the analysis and explanation of human lives, used by researchers from a number of different disciplines. Anthropologists have focused on the process of socialization by which one age stratum is taught to succeed the next over the life cycle, linking social roles to the cultural system of beliefs and values. Age-set societies have been intensively described because of the very visible structure of age stratification and the explicit grouplevel patterns of life-cycle stages. Rites of passage are the symbolic counterparts of age-set transitions from one age stratum to the next, marking the personal change and announcing it to the entire community.

Developmental psychologists have used the life cycle as an organizing principle for specifying the steps in human development. The process of aging drives this principle, which is defined and structured by social organizations and individual roles. A prominent example is Erikson’s eight stages of life (1968). In this model, psychosocial stages are identified, consisting of times in which opportunities for success and the risk of failure are present. For example, the young adult stage is marked by the capacity for intimacy versus isolation, and integration, while a choice between wisdom and despair marks old age. The passage from one of the eight life stages to the next is regarded as a turning point that is fraught with vulnerability and heightened potential.

The life cycle forced gerontologists to recognize that the study of old age in isolation from the

prior life cycle is not viable. The economic resources, health, knowledge, and family situations of the elderly result from the cumulating of life-cycle experiences. These same factors influence the chronological age at which people take on characteristics of the aged. Gerontology as a field has expanded to encompass the dynamics of life-cycle transitions. Immediately noteworthy when one adopts this aging approach is the fact that persons currently reaching old age have prior life-cycle experiences that may better prepare them for becoming old than did prior cohorts. The sociological interest in aging motivates gerontologists to attend to both the lifelong process of aging and potentially dramatic intercohort changes in successive cohorts of the aged.

Life Cycle Squeeze. Economists have relied on the life cycle and the gendered division of labor to study household and family economics. Wages follow a curvilinear pattern over the life cycle: Young workers receive the lowest wages; wages increase over the life cycle, peaking at midlife; while workers older than 55 tend to experience stability or even a decline in earnings. Women’s earnings show much less of an age profile, both because young women frequently interrupt or reduce labor-force involvement when children are born, and because women’s jobs are less likely to take the form of careers in which progression upward from one job to the next occurs.

This life-cycle pattern of earnings does not always match family income needs. Early in the life cycle, children are net consumers of income. As societies require a more educated population, youth and adolescents also become net income consumers. While this has long-term payoff for the society and for new cohorts of workers, it increases the costs and reduces the economic value of children to families. These costs most often occur when workers are at the low point in their earnings. Later in the life cycle, earnings are higher but the cost of a college education and assisting children in getting started also may be high. At the same time, elderly parents may become a social and financial obligation for children, leading to the powerful concept of the ‘‘life-cycle squeeze.’’

Cohorts facing this new mix of obligations with the traditional earnings profile have acted to reduce desynchronies in the stages of the life cycle.

Credit mechanisms (for example, long-term mortgages, home equity loans to pay for college education) smooth income and costs over the lifetime. The intercohort upgrading of the situations of the elderly in the United States means that parents become dependent on their adult children at an older age. The government has intervened to bear much of the cost of the elderly. Life-cycle pressures have also resulted in intercohort changes in the content of the life cycle of men and women— delays in marriage and first birth, a reduction in family size, the shift to two-earner families, and increases in divorce.

Sociologists have devoted considerable attention to the cohort-level study of life-cycle transitions. Turning points imply inevitability and potential crisis. Sociologists study the form of the transition (for example, cohabitation or marriage), whether or not a transition occurs (for example, parenthood), and the average age and variability in age of a transition across individuals of the same cohort. This approach recognizes (building on the idea of an age-stratification system) that a variety of transitions are crosscutting (for example, work and marriage, birth of a first child and marriage).

The Life Cycle in Demographic Models. It is the educational, labor-force, and family outcomes that interest demographers. The study of family life has proceeded with the measurement of marriage and then the progression to first birth, second birth, and so forth (taking into account both the number and the timing of births). A special tool called parity progression analysis has enabled demographers to identify turning points in fertility decisions, and how these have changed across cohorts. This approach to the study of demographic life-cycle stages, along with the recognition that fertility is inherently a biological process, has led demographers to develop population models of fertility that take into account marriage patterns, the level of marital fertility, and birth limitation. The life-cycle model also has informed research on age patterns of migration, and its regularities across time and place.

The life-cycle perspective has produced a variety of unexpected results. The American baby boom of the late 1940s and the 1950s was largely due to the temporal coincidence of childbearing by successive cohorts, rather than to a dramatic increase in family size. During the baby boom,

women 35 and older made up childbearing that had been delayed by the Great Depression and World War II. Women reaching adulthood during the baby boom years responded to favorable economic conditions for young families by having their first child at a younger age and having subsequent children more quickly.

Family Life Cycle. Family sociologists made a great leap in developing the family life cycle as a variant form of the life cycle (Glick 1965). The family life cycle is unusual in that it focuses on family formation and childbearing, ignoring such linked transitions as completion of schooling and work. The family life cycle stretched the life-cycle model to incorporate role changes associated with the transitions of other individuals. (For example, a husband makes the transition to marriage at the same time as the wife. Only when all children grow up and leave the home does the family experience an ‘‘empty nest.’’) The family life cycle became a predominant research paradigm in family studies.

The family life cycle can be a useful analytic tool for understanding the succession of family roles in populations in which families predominate over individual interests. The family life-cycle model works only for those populations in which marriage precedes childbearing, the ages of each are specified within a narrow time band, and marriages do not end (by widowhood or divorce) before the last child leaves home.

None of these assumptions are even approximately satisfied for the United States. First births often precede marriage (among blacks this is the typical pattern). Many couples postpone childbearing within marriage, and as many as one-fifth remain voluntarily childless. Over half of all first marriages end within twenty years. Remarriage often follows. This degree of inconstancy in household membership begs the question of how to define the family whose life cycle is being described, and followed over time. The family life cycle is now widely regarded as a useless conceptual tool because it utterly fails to capture the realities of contemporary family life.

LIFE CYCLE AND LIFE COURSE

The life cycle defines pathways for individuals as they age from birth to death, specifying usual expectations about the sequence and timing of

roles (for example, a first birth when married and at age 18 or older). Empirical research that uses the life cycle to analyze the lives of population cohorts typically find that these life-cycle stages, as socially defined and demarcated, follow expected patterns.

Research on the transitions of individuals over their lifetime has demonstrated the essential incorrectness of this supposition. For many individuals, childbearing precedes marriage, parenthood occurs when the parents are not yet economically self-sufficient, and adult children return to their parental household after they have assumed (and sometimes failed at) adult family and economic roles. This has caused researchers to consider whether new life-cycle patterns are emerging, or whether a group of individuals is somehow ‘‘deviant’’ from the established life cycle.

Clearly there have been marked intercohort changes in the life cycle, reflecting the varying opportunity structures of time periods and cultural change. For example, the availability of the GI Bill for college education and interruptions in education associated with wartime military service allowed many men to marry and have children before they finished school and became economically established. In recent cohorts of young women there is a decreasing emphasis on the necessity of marrying before having a child, and, on the part of all adults, a greater readiness to assist rather than condemn single mothers.

An even greater source of departure from the population life-cycle model is the large number of persons in each cohort who never make a transition to a given life-cycle stage (e.g., those not marrying or not becoming parents), who retreat from a given life-cycle stage to an earlier stage (e.g., fathers who divorce and abandon their families, and retired persons who return to work), and who are not part of the typical life cycle (e.g., the severely disabled, persons who die before reaching old age). These features of the life cycle vary by such primary sociological variables as social class origin, education, race and ethnic group, and place of residence.

Among Americans the seeming conformity of cohorts to the life-cycle patterns masks the overwhelming number and frequency of individual departures. In this situation the life cycle seems to be a far less useful analytic device. Social scientists

have adopted in its place the more sophisticated and flexible ‘‘life-course’’ perspective. The life course sees individual lives as a series of trajectories (such as family or career) that are socially recognized and defined. Age is significant in the life-course approach because it is an indicator of biological aging and locates individuals in historical context through birth cohorts. The social meaning of age helps define life-course pathways (recognized routes of trajectories) through age norms and sanctions, and social timetables for the occurrence and order of events. Transitions (leaving home, getting a job, marrying) define trajectories. Interlocking transitions and their trajectories lead to multiple roles that define the individual life course from birth to death.

Because of the emphasis on variations in trajectories across individuals, every individual life course has the potential to be unique. Much of the population-level research with the life-course model has focused on transitions—the proportion of cohorts making a transition, average age at transitions, and the range of ages at which cohorts typically make these transitions. The life cycle gives analytic meaning to these life-course transitions by providing a standard against which to measure how transitions vary across cohorts and differ among key population groups within cohorts.

Causal analyses of the life course are usually done at the individual level, typically with a class of statistical methods called ‘‘event history’’ or ‘‘hazards’’ models. These statistical methods enable investigators to examine empirical data on individual transitions, modeling the age-graded pattern of transitions from one social role to another and identifying ‘‘heterogeneity’’ (sources of variation in transitions at the individual level).

The Necessity for Life Cycle in Studies of the Life Course. This points to a dilemma for social scien- tists—the very life-cycle model that the life-course approach undermines provides the essential theoretical framework that gives meaning to individual behaviors. Because social scientists are part of the societies they study, they also carry in their own heads models of the life cycle—what should be done when it should be done, and what denotes success or failure. The life-course perspective on pathways that define typical trajectories and the social meanings of age capture the essence of a lifecycle model. The apparent tension between the