by Carl Haub, senior demographer, Population Reference Bureau
No demographic subject captures writers’ imaginations like a country’s birth rate, be it baby “booms” or “busts,” or record highs or lows. But what measure should you use when you’re writing about the birth rate? Yes, there’s more than one—there are three: the crude birth rate, the general fertility rate, and the total fertility rate. In this blog post, I want to clear up the confusion.
First, we’ll take the crude birth rate (CBR), which is simply the number of births in a year per 1,000 population. Rates have a numerator (in this case, births) and a denominator (the country’s total population). The fact that the denominator is the total population of all ages is the reason why the CBR is labeled “crude.” In 2011, the CBR in the United States was 12.7 births per 1,000 population. But the CBR can be significantly affected by age structure, so that a population with a high proportion of elderly will tend to have a lower rate than one with a younger population. Why bother to report it? Because the CBR is one of three essential parts of the national population growth rate, since populations grow or decline based on the number of births, deaths, and net immigration—the balance of people moving in and out.
Second, we have the general fertility rate (GFR), which is similar to the CBR, but the denominator includes only females of childbearing age, usually ages 15 to 44 or 49. It is certainly true that the GFR is more “refined” than the CBR and its denominator more appropriate. For year-to-year changes in the birth rate, it is a better indicator since the childbearing-age group changes little but, over the long term, it can be affected by such changes.
But, don’t we really want to know how many children women will end up with when they finish their childbearing years? Annual birth rates can be distorted because women delay having children—so it looks as if they will have fewer children than they ultimately do. No rate for a single year can measure exactly that.
The total fertility rate (TFR) tells us what we are looking for, the one that measures annual trends with no effects of age structure as mentioned above. The TFR shows how many children a woman would have in her lifetime if the pace of childbearing of a given year remained unchanged. It is derived by simply adding up age-specific birth rates, the total being that average number of children. To explain, we take the sum of the rates for women ages 15, 16, 17…up to 44 or 49 to get a precise snapshot of the TFR.
Several recent articles have reported that, in 2011, the U.S. birth rate reached its lowest point in history. But that was in terms of the CBR and GFR. For example, in 2011, the U.S. TFR was reported by the National Center for Health Statistics to be 1.89 children per woman and the GFR, 63.2. But 1976 had, and still has, the lowest TFR ever reported, 1.74. However, the 1976 GFR was 65.0, higher than in 2011. Why? Because the female childbearing population was “younger,” with a higher proportion in their 20s. But they were having children at a slower rate than those in 2011. Not convinced? Consider this: If women in 1976 had the same TFR as women did in 2011, they would have borne 3,265,869 children. But they didn’t. They had 3,167,788. So, when you are trying to find the apples-to apples way to look at a country’s trend in the birth rate, there really is only one choice, the TFR.