Measuring Marital Fertility Control with CPA

Abstract

Cohort Parity Analysis (CPA) is an indirect method for measuring the extent and timing of the adoption of fertility control within marriage. Cohort Parity Analysis uses 2 sets of parity distributions, 1 from the population under study (the "target" population) and 1 from a similar population in which fertility control is absent (the "model" population). Fertility control is defined as any set of behaviors in the target population that cause its parity progression rates to differ from those of a similar but noncontrolling population. The target population contains an unidentified mixture of controlling and noncontrolling couples for a given age range and marriage duration. The model population is similar in all respects except that it contains no controllers. Examples are taken from urban and rural Irish populations in the 1911 census data. Cohort parity analysis rests on 2 basic assumptions: 1) For every specified marriage duration and marriage age, there exists some parity above which controllers are never found; and 2) Parity progression rates of those in the mixed population who have never initiated fertility control are identical to those in the model population. Further, one must identify a cutoff parity beyond which controllers are presumed not to be found. In these urban Irish examples cutoff parity for each marriage age and duration is set at 20% of that of the noncontrolling rural Irish population. The upper and lower bounds on the percentage of controllers are derived by obtaining the lower and upper bounds on the size of the group at that parity who never controlled and subtracting these estimates from the observed percentage of the target population observed at that parity. Flow charts are used to present the methodology of cohort parity analysis in a simple format. the method is illustrated in the case of Ireland in 1911. Aggregate parity distributions for the county boroughs of Dublin, Belfast, Cork, LOndonderry, Limerick, and Waterford are taken as the target distribution; and parity distributions for those living outside the county boroughs are taken as the model distributions. The analysis shows that 28% of urban-dwelling Irish women who married before age 30 and were married between 4 and 29 years in 1911 used some effective means of fertility control. The parity distributions also show that women who married later controlled their fertility to a greater extent and that between 20.9 and 25.5% of women married 4 years in 1911 had already practiced fertility control by 1911, but only 15.5% of those married 15-19 years had used fertility control by 1911. Cohort Parity Analysis is thus a useful method of examining historical populations in the process of fertility transition.