The three commonly used research designs-tables of rates or proportions, repeated cross-sectional sample surveys, and accelerated longitudinal cohort designs-described in the previous chapter can be used for age-periodcohort (APC) analysis. The use of suitable data alone, however, does not guarantee proper inferences regarding A, P, and C effects. Analytic approaches are often critical in determining the attribution of variations in the outcome of interest to distinct inuences of age, period, and birth cohort. As noted previously and discussed in detail in this chapter, the APC underidentication problem, or the “APC conundrum,” has been a point of methodological controversy for decades, with little agreement on a systematic set of interrelated models and methods for analysis. Perhaps fueled by this lack of agreed-on methodological procedures for analysis, APC problems and controversies also have ared up from time to time in empirical analyses of substantive questions in the social sciences, some of which have been introduced in Chapter 3.