AGING AND THE LIFE COURSEoutcome, with relatively short-term trajectories of
death, chronicity, recovery, and relapse).
Trajectory-based research relevant to our un-
derstanding of middle and late life is gradually
accumulating. This is especially true for long-term
patterns of health and functioning, providing evi-
dence about both the dynamics of disability during
late life (e.g., Maddox and Clark 1992; Verbrugge,
Reoma, and Gruber-Baldini 1994) and long-term
patterns of stability, improvement, and decline in
health over the course of adulthood (e.g., Clipp,
Pavalko, and Elder 1992). Important trajectory-
based research on pathways to retirement (Elder
and Pavalko 1993) and place of death (Merrill and
Mor 1993) is also available.
The concept of trajectories has been valuable
in theoretical development, as well as empirical
inquiry. The theory of cumulative advantage/disad-
vantage has intersected well with studies of life-
course trajectories. This theory posits that hetero-
geneity is greater in late life than earlier in the life
course as a result of the accumulation of assets
(advantage) or liabilities (disadvantage) over time.
The theory of cumulative advantage/disadvantage
has been especially useful in understanding so-
cioeconomic heterogeneity in late life, especially
differences in total net worth (e.g., Crystal and
Shea 1990; O’Rand 1996). However, it can be
applied to other sources of heterogeneity in late
life as well (e.g., health). Investigators who prefer
examination of the multiple distinctive trajecto-
ries within a sample would offer a caution to
cumulative advantage/disadvantage theory, how-
ever. They would note that although trajectories of
increasing and decreasing advantage are undoubt-
edly common, there are likely to be other impor-
tant trajectories as well—e.g., a trajectory of cumu-
lating advantage that is reversed as a result of a
personal (e.g., serious illness) or societal (e.g.,
severe economic downturn) catastrophic event.
Person-centered research. A more recent con-
tribution to the sociological armamentarium for
understanding aging and the life course is person-
centered research. As the label implies, the focus of
this emerging research strategy is to analyze ‘‘peo-
ple’’ rather than ‘‘variables.’’ In practice, this means
that members of a sample are first grouped in-
to subsets on the dependent variable of inter-
est. Subsequently, those categories are further
disaggregated into groups based on distinctive
pathways or life histories associated with the out-
come of interest.
Work by Singer, Ryff, and Magee (1998) pro-
vides the richest example of person-centered ag-
ing research to date. The dependent variable of
interest was mental health. In the first stage of
their research, groups of middle-aged women were
divided into groups that differed on levels of
mental health. Subsequently, the large archive on
longitudinal data obtained from these women over
the previous three decades was examined to iden-
tify distinctive pathways associated with mid-life
mental health. For example, the group of women
who exhibited high levels of mental health and
well-being were further subdivided into two groups
that Singer et al. (1999) labeled the healthy and the
resilient. Healthy women were those who had life
histories that were relatively free of major stressors
or traumas, enjoyed adequate or higher levels of
social and economic resources, and exhibited sta-
ble patterns of robust mental health. Resilient
women were those who had achieved robust men-
tal health at mid-life despite earlier evidence of
poor mental health and/or histories of stress
and/or inadequate social and economic resourc-
es. Clearly the life histories of women who were
mentally healthy at mid-life varied in important
ways. Moreover, the healthy women illustrate the
benefits of leading relatively ‘‘charmed’’ lives, while
the resilient women help us to understand the
circumstances under which ‘‘risky’’ life histories
can be turned around to produce health and
personal growth.There are clear similarities between person-
centered research and trajectory-based research.
Both are based on long-term patterns of change
and stability and both are designed to understand
both life-course dynamics and heterogeneity in
those dynamics. But there also are important dif-
ferences between the two approaches. In trajecto-
ry-based research, the trajectory or pathway itself
is the ‘‘dependent variable’’ of interest and the
‘‘independent variables’’ are factors that have the
potential to alter the shape(s) of those pathways. In
person-centered research, the ‘‘dependent vari-
able’’ is an outcome of interest (e.g., mental health),
and trajectories of the ‘‘independent variables’’
are constructed to explain that outcome. Both are
currently at the cutting edge of research that at-
tempts to simultaneously examine life-course dy-
namics and life-course heterogeneity.