A model of fertility by planning status.

Data from the 1965 and 1970 National Fertility Studies are used to produce classifications of births and exposure to births by planning status for real and synthetic marriage cohorts, covering the experience of the 1940s, 1950s, and 1960s. Indices of reproductive input (three ends, three means, and three conditions) and of conventional reproductive output (such as the mean number of unintended births) are derived from these observations. The outputs are expressed as deterministic equations in terms of the inputs; this permits the study of the structure of fertility determination. The model provides a parsimonious description of the sources of change in fertility and an instrument of possible use in policy.