COHORT PERSPECTIVESHis classic work on ‘‘demographic translation’’
sets out the mathematical procedure for moving
between the cohort and the period ‘‘modes of
temporal aggregation’’ (Ryder 1963, 1983).
Central to this method is the identification
problem confounding many attempts at cohort analy-
sis. This problem occurs from efforts to interpret
the separate effects of three concepts—cohort,
period, and age (C, P, and A)—when only two
variables, such as date and years of age, are in-
dexed. Apart from various procedures that as-
sume one of the parameters is zero, the most
appropriate solution to this problem is to specify
and measure directly the three concepts used in
the particular analysis (Cohn 1972; Rodgers 1982;
Riley, Foner, and Waring 1988, pp. 260–261).
After all, as Ryder puts it (1992, p. 228), the cohort
(C) is a set of actors, the age (A) is their age, and the
period (P) stands for the social context at the time
of observation..
Wide Range of Methods. Ryder’s exegesis of
this particular method illustrates, through its
strengths and limitations, the utility of the tripar-
tite conceptualization of cohort perspectives as a
heuristic guide. The strengths in Ryder’s formula-
tion focus exclusively on the significance of co-
horts as a macro-analytic vehicle for social change.
In the broader cohort perspectives outlined here,
many other methods are useful for specific objec-
tives where cohort analysis is inappropriate. Some
employ a cross-sectional approach. Others utilize
intercohort comparisons to focus on aging proc-
esses at the individual as well as the collective
levels. Still others complement demographic analyses
of populations with examination of the related
structures of social roles and institutions.
Thus, despite its signal contributions, neither
cohort analysis nor any other single method can
comprehend the full power of cohorts as ingredi-
ents of aging processes, age composition, and the
complex interplay with social structure.
(SEE ALSO: Structural Lag)
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