An integrated formal demographic fertility framework

The traditional framework of fertility research conceptualizes childbirth from the mother's perspective. From her perspective, birth is an uncertain and potentially recurring event. In contrast, the Born once, die once (B1D1) framework conceptualizes birth as an event experienced by the child. From its perspective, birth is certain and, like death, occurs only once. As an advantage over the traditional approach, the child's perspective allows for the use of density, survival, and hazard functions to study fertility age patterns at the macro level using birth counts for all parities by maternal age. Here, we reformulate the B1D1 framework using fertility rate notation and extend the traditional fertility framework by analogous density, survival, and hazard functions. We compare this extended traditional framework with the B1D1 framework using data on Swedish cohorts born in the 19th and 20th centuries. Large historical differences between the density, survival, and hazard functions in the two frameworks have diminished for more recent cohorts, suggesting converging conclusions about fertility age patterns. The new density, survival, and hazard functions can shed new light on differences in fertility age patterns across populations and advance traditional fertility research, including by capturing fertility and mortality age patterns with common concepts and measures.