(September 2002) When it comes to predicting baby booms, historical analogies are not very useful. That is why, in the wake of the terrorist attacks last Sept. 11 in the United States, neither demographers nor anyone else can say what might happen to birth rates, because there has never been an event just like 9/11.

Fertility rates have been rising at a modest rate for nearly two decades. Since the mid-nineteen eighties, fertility rates have crept up slowly to the replacement level, rising from 1.8 to just over 2.1 children per woman. Demographers have gotten used to predicting that next year's fertility rates will be just a shade more than this year's, with no sudden jumps or crashes. Most see no reason to change that rule of thumb now. A sudden event, even one as traumatic as the 9/11 attacks, seems unlikely to disrupt such a well-established national trend.

Many commentators have likened the terrorist attacks to the attack on Pearl Harbor in 1941, which also elicited a national reaction of surprise and anger. But after Pearl Harbor, millions of young men left home for three or more years; that by itself had both a demographic and an economic impact. Thousands of lives have been disrupted by the loss of a husband or wife in the 2001 attacks, and thousands of men and women have been deployed in the armed services for the war on terror — but not millions. For most Americans, the impact of 9/11 is indirect. We are still at home, still living with the same people, and still doing the same jobs as before 9/11.

There is a folk memory or urban legend of a baby boomlet after the great blackout that affected the whole northeastern United States in 1965. There was no effect on fertility rates after that event, despite widespread stories of conceptions in stuck elevators and TV-less apartments.

These stories get reinforced because on any given date, nine months after any event one cares to name (gestation times vary, and the average is more like 40 weeks than nine months), at least one hospital in any county or metropolitan area will report an unusually high number of births, and at least one obstetrician will be feeling overworked. A diligent journalist can make some phone calls, find that hospital or that obstetrician, and write an article about the apparent baby boom. But if other hospitals and other obstetric practices had low counts that day, and the counts even out on average, then no effect will be seen on fertility rates.

There have been some studies showing regional effects on U.S. fertility rates of sudden disruptions of economic life (like Hurricane Andrew) or of social life. Ronald Rindfuss, of the University of North Carolina, and his colleagues found lower fertility rates than expected from long-term trends among southern whites following the court decisions mandating racial integration of schools in 1954 and after. The explanation seems to be that many white couples, perhaps not consciously, felt uncertain enough about their future to postpone having children. Following this precedent, demographers might within a few years be able to detect an effect of 9/11 on fertility rates in a few regions most directly affected, likely spread out over a few years.

It will take time to find such an effect, if it exists, in part because it takes time for changes in behavior to be picked up in birth rates, especially for small areas. There are always fluctuations in the number of births, marriages, divorces, and deaths in a small area or over a short period. Several years of data for an area less than the whole country, say a state or region, are needed to distinguish short-term fluctuations from a long-term trend.

The terrorist attacks may well have affected decisions about the most basic aspects of life for most Americans. But people could still respond in different ways. For some people, the sudden reminder that death could come at any time may lead them to think, "We always meant to have children; let's stop putting it off." For others, as Duke University professor S. Philip Morgan points out, uncertainty about the future may lead them to think, or just to feel, that the time isn't right to be starting a family.

In a big, diverse country, the same event can evoke very different responses by individuals, leading to fascinating stories, but little for demographers to analyze.

When Will We Know?

The National Center for Health Statistics (NCHS), part of the Centers for Disease Control and Prevention (CDC), calculates and publishes fertility rates as part of the national vital statistics program. The NCHS relies on state agencies to report data from birth and death certificates. It takes time for states to collect all the certificates, send in their reports, and for NCHS to study the state reports, resolve discrepancies, edit errors, and calculate the rates. Each year, around June, the NCHS publishes preliminary annual data, often with estimates for one or more states that have not reported final data yet. Later, the final report for the year is issued.

Monthly reports that could reflect changes in birth rates during the summer of 2002 (and thus the immediate impacts of changes in the rate of conceptions beginning in September 2001) will not appear until some time in the summer of 2003.


John Haaga is director of domestic programs at PRB.


For More Information

As of September 2002, the most recent publications are preliminary data for births during 2001 and a final report for births during 2000 (available on the NCHS website): www.cdc.gov/nchs/births.htm


Box 1
Boom and Bust

During the baby boom of 1946-1964, U.S. fertility rates were unexpectedly high, at one point almost reaching the levels that would have resulted in the average American woman having four children over her lifetime. During the baby bust of the 1970s, rates fell well below the level at which a population can replace itself in the long term without immigration (roughly two children per woman). Since the mid-1980s, fertility rates have crept back up slowly to the replacement level, rising from 1.8 to just over 2.1 children per woman.