Old Age And Centenarians Research Paper

1. Is Old Age One Or More Life Phases?

Several authors propose that it might be appropriate to consider old age as involving not one but several life phases. Some researchers distinguish the Young Old from the Old and the Oldest Old (e.g., Neugarten 1974, Suzman et al. 1992) whereas others refer to a Third Age and Fourth Age (e.g., Laslett 1991, Baltes 1997, Baltes and Mayer 1999).

What is the basis of these proposed classifications? Neugarten (1974) coined the term young old to identify a group of retirees that was not so much identifiable in terms of chronological age but rather by their relatively good health status and social engagement. Based on demographic features, Suzman et al. (1992) identified 85 years of age as the criterion of membership in the oldest old category. The population over age 85, unlike any other age strata, is typically characterized by a unique excess of women over men, higher levels of comorbidity and institutionalization, and greater consumption of medical and care services. Individuals born between 1890–1915 who comprise the oldest old observed in 2000 also exemplify a set of characteristics that are cohort-specific: for example, they have a lower level of education compared with subsequent cohorts, and a higher likelihood of long-term widowhood.

The term Third Age was used in the title of Les Universites du Troisieme Age in France in the 1970s, and later in 1981 at Cambridge University to characterize a program designed for an older (senior) group of students with the end-purpose not being professional entry but rather lifelong personal education (Laslett 1991). Laslett described the Third Age as an era of personal achievement and fulfillment and the Fourth Age as an era of final dependence, decrepitude, and death. In Baltes’ (1997) use of the distinction, the criterion is a dynamic and changing one. He proposes that the onset of the Fourth Age be considered as the chronological age where 50 percent of the birth cohort has died. At that age, processes of biological aging can be expected to be predominant in the aging process.

At the end of the 1990s, a number of cross-sectional and longitudinal studies began to focus not only on the demographic, health, and social distinctions between the proposed phases of old age, but also on possible differences in psychological profiles. Examples include representative surveys such as Asset and Health Dynamics of the Oldest Old (AHEAD: Soldo et al. (1997), the Berlin Aging Study (BASE: Baltes and Mayer 1999), Danish Twin Study (Andersen-Ranberg et al. 1999), and the Swedish Adoption Twin Study of Aging (SATSA: McClearn et al. 1997). Although centenarians have become a target group for biodemographers (e.g., Vaupel et al. 1998), well-designed psychological studies of representative samples of centenarians were rare in the year 2000.

2. Central Theoretical Questions About Old Age

Psychological theory and research on old age has been shaped by three general goals:

(a) to map trajectories of change in specific domains of psychological functioning during old age (e.g., cognition, personality, and social behavior) and determine processes underlying change;

(b) to determine the sources of observed heterogeneity in psychological functioning and longevity in individuals over the age of 70 years; and

(c) to understand systemic interdependencies across domains of functioning and subgroup differences.

Historically, the prime focus has been to determine average patterns or trajectories of within person (intraindividual) change over time (aging) in terms of level, direction, and rate. Research questions have centered on factors linked to the onset and rate of decline as well as asking whether decline goes hand in hand with structural dedifferentiation (e.g., reduced complexity) or structural disorganization (break-down).

2.1 Proposals About Trajectories Of Change

Although decline is the expected trajectory of change in old age, there are several proposals about differences in the nature, rate, and onset of decline. To begin, it is considered important to separate decline trajectories that are pathologically determined from those that are normative (i.e., usual and age-related) and to determine to what extent interventions (e.g., memory training, social contact) can modify the onset and rate of decline (e.g., Rowe and Kahn 1987). Analogous to the study of early versus late (delayed) development or maturation in early life, there is an interest in the identification of factors linked to the delayed onset of multiple negative changes in old age (e.g., compression of morbidity; see Fries 1980). Death-related trajectories (terminal decline) have been distinguished in intellectual functioning and some indicators of perceived well-being (e.g., subjective health, depressivity; see Berg 1996). These decline trajectories are larger and qualitatively different from normal age changes and occur during a window of 5–7 years before death. Birren and Cunningham (1985, p. 23) suggested that terminal decline represented the emergence of a cascade of structural change.

Trajectories reflecting a relative maintenance of functioning and delayed decline have been labeled ‘successful aging.’ These provide insight into what might, in principle, be possible for increasing numbers of older persons, given the evolution of social and cultural environments supportive of old age (Baltes 1997). Baltes characterized successful aging as the potential to maximize the gains of a long life and minimize the losses inherent in old age. Successful aging is indicated by high life quality, subjective well-being, relative good health, and longevity. Rowe and Kahn (1997) suggested that these outcomes reflect the interrelationships of three components: low risk of disease and disease-related disability; high cognitive and physical functional capacity; and an active engagement with life (especially positive interpersonal relations and productive activity).

Do trajectories of change differ among domains of psychological functioning in old age? Research published until 2000 suggests that, at least up to the early eighties, cognitive functioning is more vulnerable to decline than is the case for other areas of psychological functioning such as personality, well-being, or social relationships (Baltes and Mayer 1999). A multitude of training and intervention studies have shown that although some aspects of cognitive decline can be alleviated or compensated, it is not possible to restore performance on cognitive tasks involving memory or perceptual speed to levels that might have been achieved by individuals when they were younger. Personality dispositions are thought to show structural and interindividual stability at least into the late seventies. Analyses of large cross-sectional and longitudinal samples of individuals aged 35–84 years suggest age-related changes in the expression of the five major personality dispositions: age gradients for Extraversion, Neuroticism, and Openness are generally negative, and those for Agreeableness and Conscientiousness are positive (e.g., McCrae et al. 1999). Proposals about changes in subjective and emotional well-being in the period of very old age are inconsistent (e.g., Diener et al. 1999). Whereas well-being may be sustained in the Third Age, the Fourth Age appears to be a phase of life that places great demands on the self-regulatory capacities of individuals.

2.2 Heterogeneity In Old Age

Gerontologists and lifespan theorists generally assume that interindividual differences are due to the cumulative effects of biogenetic, health, and personal life history factors. This assumption opens a realm of questions about the distribution of interindividual differences and whether this distribution expands or contracts in range in old age. Three positions on these questions reflect different lenses on the forces of heterogeneity across the life course.

The first position argues that early adult life is a phase when within-cohort heterogeneity expands greatly, and that the consequences of this expansion are maintained for the rest of life. Young adulthood, for example is a life phase that stimulates the initiation of a wide range of life courses in terms of education, work, family, and health behaviors (e.g., Elder 1998, Vaupel et al. 1998). The second position suggests that interindividual heterogeneity may increase with age (e.g., Dannefer 1988). The combined effects of unique experiences over many years should magnify differences between individuals. Genetically-based differences would also have had more time to be expressed and to contribute to divergence. Moreover, older adults, somewhat freer from social constraints, might be more likely to select their own courses of action. Counter to these two positions is a third proposal that, at least among the oldest old, we may observe reduced heterogeneity for those aspects of functioning that predict longevity because of selective survival (see Sect. 3, however).

2.3 Subgroup Systemic Differences In Functional Profiles

Gerontological researchers have long searched for subgroups exemplifying patterns of aging associated with differential survival, pathology, and lifestyle (e.g., Williams and Wirths 1965). Underlying this search is the concept that, over time, subgroups reflect the systemic operation of different combinations of psychological profiles. Early ideas about successful and less-successful lifestyles, and subgroups of normal versus pathological agers have been advanced in subsequent research with representative samples (e.g., Rowe and Kahn 1997). Smith and Baltes (1997), for example, reported nine subgroups extracted from the Berlin Aging Study, four reflecting different patterns of desirable functioning and five less desirable functioning. The relative risk of membership in the less desirable profile groups was 2.5 times higher for the oldest old than for those aged 70–84, suggesting a systemic transition in psychological functioning in the Fourth Age. It is an open question whether centenarians share a common profile of psychological characteristics (e.g., intellectual abilities, personality characteristics, lifestyle behaviors, belief systems) that contribute to and afford adaptation to a long life.

3. Research Issues

Researchers interested in understanding the processes underlying trajectories of change and subgroup differences in old age are faced with the difficult task of separating the effects of several explanatory sources: factors that are age-related, pathological, death-related, cohort-related, and factors associated with sample selectivity and selective mortality.

In research design, chronological age is often used as a proxy for the time interval required for change to occur, and researchers translate their findings about change (or age differences in cross-sectional studies) into age functions or age trajectories. Some processes of change in old age, however, may instead be time-dependent (e.g., require a certain length of time to occur) or death-related (e.g., co-vary with factors associated with distance from death). Self-regulation is an example of a time-dependent process: Time is required to adjust to a life event or new health-related constraint. Some time-dependent processes may also interact with age (e.g., the young old and oldest old may differ in adaptation or recovery time).

The extent to which selective survival represents alternative explanations for observed group differences in cross-sectional and longitudinal designs is a general problem of research on advanced old age. Selective survival effects can be manifested in means, variances, and the patterns of intercorrelations between variables, and will appear for all variables that co-vary with the variables on which the selection is defined (Nesselroade 1988). For each year above average life expectancy, individuals who survive represent a proportionately more select subgroup of their birth cohort. Because data on the nonsurviving members of the cohorts are usually not accessible, we do not know whether the selection effects nullify, create, or diminish observed differences. With regard to gender, the suspicion is that the ‘structural’ compositions of samples of older men and older women differ because of gender differentials in longevity (Smith and Baltes 1998). Compared with older women, samples of older men are probably more positively selected on factors that contribute to longevity (especially sex-specific factors). Precisely what these factors might be is an open question (see Wachter and Finch 1997).

The selective survival component clearly sets a constraint on the interpretation of findings about age and gender differences in the period of very old age. A further constraint is introduced by sample selectivity (i.e., the question whether the younger and older men and women who agreed to participate in the study represent the heterogeneity of their respective surviving population subgroups). Sample selectivity is a particular issue in many studies of centenarians. If researchers screen for dementia, the psychological profiles that are reported from many studies only reflect cognitively well-functioning centenarians (estimated dementia prevalence at age 100 is 40–60 percent). Furthermore, time of data collection together and cohort-specific experiences make it difficult to generalize findings about predictors of longevity.

4. Future Directions

Ideally, we need a combination of experimental work and multi-wave longitudinal data collected over many years, indeed until the deaths of all participants, in order to understand fully the mechanisms and processes of psychological change in old age. Longitudinal studies should be designed so that time intervals between measurement are age-appropriate: A 7-year interval might be sufficient to observe significant change in the seventies, but will contribute to sample attrition due to mortality among 90-year-olds. A new set of studies that follow individuals 90 years of age until their death and collect extensive information about psychological functioning would provide valuable information about possible trajectories of change that distinguish centenarians from their long-lived peers who die prior to age 100. As we begin to understand more about the sources and consequences of different psychological change trajectories, we will be in a better position to intervene in the cultural and social context of old age. Revised social judgments about autonomy and dependency in old age (M. M. Baltes 1996) and the creation of supportive life environments to compensate for personal frailty may well contribute to higher life quality and a longer life in the Fourth Age of the future (e.g., Baltes 1997, Olshansky et al. 1998).

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