New York State projections 2022 - 2050

Fertility assumptions

The number of projected births is a product of age specific fertility rates and the number of women by age.

Births to women of age a = AgeSpecificFertilityRate_a * CountOfWomen_a
Total births = sum over age 15 through 44 (births to women of age a)

To create our age specific fertility rate assumptions, we used data from 2007 to 2022 on live births to women residing in New York State by age from the National Vital Statistics System (NVSS), available through CDC Wonder, and births in the past year by mother’s single year of age from the American Community Survey (ACS). Because 2020 was such an unprecedented year, it was excluded from our assumption calculations. Since the NVSS tables include births to mothers aged 45 and older and under 15, we first adjusted the total number of births for each year of the NVSS by subtracting births at ages not in our universe from the total. We applied the share of births by 5-year age group to the adjusted NVSS yearly totals, and multiplied the share of births to mothers by single years of age (SYA) from the ACS with the 5-year age group births to get SYA birth estimates that were consistent with the NVSS totals. Since births by mother’s SYA were also available in the NVSS we were able to directly apply the share of births from the NVSS to mothers aged 15-19 by single year of age (SYA) to the adjusted NVSS total. We took the average number of births by SYA over all 15 years and recorded the Total Fertility Rate (TFR) and summary statistics. We then computed a Romaniuk Three-Parameter Model of fertility based on these values. The TFR (scaling parameter T) was 1.7, and the desired duration of our curve was 29 (ages 15 to 44). The average age at birth (A) from our analysis was 30.6 while the modal age (M) was 31. The result is a bell curve age distribution of fertility, slightly skewed to the left, that peaks at age 31.

The age specific fertility rates was derived as an average over several years, but the TFR has gone down and was around 1.6 at the end of the previous decade. In our scenario's we assume returning to a TFR of 1.6 in the middle scenario, but an increase to 1.65 in the High and a decrease to 1.55 in the Low scenarios.

To determine the number of boys and girls among the newborn, we assumed a sex-ratio at birth of 1.05.