November 28th, 2012 | Posted in Reproductive Health
by Carl Haub, senior demographer
Several newspapers, blogs, and websites have proclaimed that the U.S. “birth rate” in 2011 was the lowest since records have been kept. But it wasn’t. The number that various sources have been calling the “birth rate” is actually the general fertility rate—that one was the lowest ever. Not the total fertility rate, which is the correct measure to use. Let me explain!
The term “birth rate” is loosely used to mean one of three commonly used measures, which demography refers to as fertility. The crude birth rate is annual births per 1,000 total population; the general fertility rate is annual births per 1,000 women of childbearing age; and the total fertility rate is the average number of children women would bear in their lifetimes if the pace of childbearing remained constant for the long term.
What is right: The preliminary report by the U.S. National Center for Health Statistics noted that the general fertility rate (GFR) of 63.2 for 2011 was the lowest ever reported. In fact, the crude birth rate (CBR) of 12.7 was also the lowest ever. But neither is the best way to capture the birth rate. Why? Because both of these measures are affected by age structure. The general fertility rate can also be affected by a population’s age structure within the female population of childbearing age, usually 15-49. The U.S. population is “older” now than it was in the past—we have more older people than younger people—and that includes a smaller proportion of younger women in the childbearing population than before.
|Crude Birth Rate||General Fertility Rate||Total Fertility Rate|
So, when we think about birth rate trends, we should really be using the total fertility rate (TFR). The TFR is “blind”—unaffected by age structure—and in showing the implied number of children women would have at today’s rate, is directly comparable over the years: apples to apples. This may be a tad confusing, but consider this: If the pace of childbearing were the same today as it was in 1976, the U.S. would have had 3.7 million births instead of the 3.9 million it did have. Why choose 1976? Because that was the year the TFR was the lowest in U.S. history and it still is. Not 2011.