Questions for Brady E. Hamilton, Ph.D., Demographer, Statistician, and Lead Author on “Trends and Variations in Reproduction and Intrinsic Rates: United States, 1990-2014”
Q: Why did you conduct this study?
BH: We produced this report because we wanted to provide an updated analysis of fertility patterns in the United States. This report provides current detailed information on the fertility patterns for the United States, as measured by reproduction and intrinsic rates, which have not been available since the release of an earlier report more than a decade ago (https://www.cdc.gov/nchs/data/nvsr/nvsr52/nvsr52_17.pdf). The new report focuses on the recent trends in these rates and also presents, for the first time, reproduction and intrinsic rates for the three largest population groups — non-Hispanic white, non-Hispanic black, and Hispanic.
Q: What is the difference between reproduction rates and intrinsic rates, and what can they tell us about population growth and change in the United States?
BH: The reproduction and intrinsic rates are important to understanding population growth and change in the United States and are useful additions to the annual birth and fertility rates (such as the crude birth rate and general fertility rate) published by NCHS. Unlike the annual birth and fertility rates which measure the fertility of women in a given year, the reproduction rates summarize the number of births expected for a (hypothetical) group of 1,000 women over their lifetime given their particular fertility and mortality rates. The reproduction rates can measure, for example, whether the number of births is at “replacement,” that is, the level at which a given group of women can exactly replace themselves. For example, the net reproduction rate in 2014 was 897 which means that given their fertility and mortality rates in 2014, we would expect to see 897 daughters born per 1,000 of these women, which is below replacement level (1,000 daughters). The reproduction rates can be used to compare populations over time or among different groups. The intrinsic rates summarize the birth, death, and rate of change of a population, which would be expected to prevail given particular fertility and mortality rates. These rates measure the change of a population, either growth or decline, and can be used to compare populations over time or among different groups. For example, the intrinsic rate of natural increase in 2014 was -3.7, which means that given the fertility and mortality rates in 2014, the population for the United States was declining. This measure excludes migration.
Q: Was there a result in your study’s analysis of reproduction and intrinsic rates in the United States that you hadn’t expected and that really surprised you?
BH: The pervasive and large declines in the rates among the race and Hispanic origin groups was quite striking. For the three largest groups — non-Hispanic white, non-Hispanic black, and Hispanic– the total fertility, gross reproduction, and net reproduction rates declined by at least 7% from 2006 through 2014. The Intrinsic rate of natural increase declined by at least 78% from 2006 through 2014 for the three groups.
Q: What differences, if any, did you see among race and ethnic groups?
BH: While the total fertility, gross reproduction, and net reproduction rates and intrinsic rate of natural increase declined for the three race and Hispanic origin groups, there were differences among the groups in the rate of decline and among the rates themselves. In general, the reproduction rates declined the least for non-Hispanic white women and the most for Hispanic women from 2006 through 2014. Similarly, in 2014, the reproduction rates were lowest for non-Hispanic white women and highest for Hispanic women. The intrinsic rates of natural increase differed, too, with the rate being negative for both the non-Hispanic white and non-Hispanic black population groups in 2014, but positive for the Hispanic population group.
Q: What is the take home message of this report?
BH: The take home message from the report is that reproduction rates and intrinsic rate of natural increase have declined overall from 1990 through 2014 and for the three largest race and Hispanic origin groups from 2006 through 2014. However, differences in the reproductive and intrinsic rates for the groups exist.