BABY BOOM, POST–WORLD WAR II

No twentieth-century demographic phenomenon in the developed countries has attracted greater attention than the "baby boom"–the sustained post–World War II fertility increases in many developed countries that produced large birth cohorts from the mid-1940s to the mid-1960s. The magnitude of the baby boom, especially in the United States, has made it a demographic event with widespread, long-lasting, and well-chronicled consequences. But demographers have focused their most serious attention on explaining why the baby boom occurred and on forecasting fertility in its aftermath. The baby boom (and the subsequent bust) is widely seen as epitomizing demographic forecasting failure. It remains demography's primary example of the unpredictability of population trends and is frequently cited as evidence that the knowledge base on human fertility is grossly deficient. However, the demo-graphic phenomena that produced the baby boom are well known, and there is a plausible social history of the circumstances that spawned that upsurge of births.

Defining Baby Booms and Echoes

A baby boom, as a generic concept, is a large increase in the number of births relative to some previous year or average (i.e., an increase in birth cohort size). This can result from two factors: a rise in the number of potential childbearers (i.e., women aged 15 to 44, partly a function of past cohort size) and the increased average risk of having a child. When fertility increases result from large cohorts entering the childbearing years (i.e., only the first factor), demographers call this fertility increase an "echo" of a previous baby boom.

The post–World War II baby boom, however, was not driven by trends in cohort size: Indeed, the boom of the 1950s and early 1960s was produced by the small cohorts born during the 1930s. (Likewise, the American baby bust of the late 1960s and 1970s occurred in the face of the maturing baby boom.) Thus, it is clear that birth rates, not generation size, have been the key factor in the postwar upsurge of births. For this reason, researchers focus attention on changes in fertility rates as the phenomena to be explained. More specifically, there is a focus on the total fertility rate (TFR)–the number of births women would have if they experienced the age-specific fertility rates of a given period.

Fertility Increases During the Baby Boom

Figure 1 shows the U.S. TFR from 1917 to 2001. The baby boom TFR maximum is 3.68, which was reached in 1957. TFR lows preceding and following the baby boom were 2.15 and 1.74 respectively. Also note that the post–World War II baby boom lasted roughly two decades in the United States. The basic features of this TFR increase can be observed in most Western developed countries. In a 1974 study demographer Arthur Campbell analyzed data for 18 Western countries with TFRs that approximated 2 in the 1930s. TFRs for these same countries were 2.7 by the early 1950s and 3.1 by the early 1960s. All of these countries experienced subsequent sharp fertility declines. By the early 1980s all of the countries studied by Campbell had TFR values below 2.1. Table 1 presents some of Campbell's data for individual countries, updated through the 1990s; all show key features visible in the U.S. data.

FIGURE 1

An additional feature of the postwar baby boom was the pervasiveness of the fertility increases and declines among subgroups within countries. For instance, in the United States all major racial and educational groups participated in both the baby boom and the subsequent bust.

In contrast to its pervasiveness across geographic areas and social groups, the baby boom can be traced to a few dynamic, demographic components. TFR changes can reflect changes in the ages that women have births (i.e., the timing or tempo of childbearing) and/or changes in the number (or quantum) of children that women eventually bear. To capture the relative importance of these changes the TFR can be usefully disaggregated into age and parity components. This disaggregation allows measurement of timing (or tempo) and number (or quantum) changes.

Table 2 shows demographer Norman Ryder's classic decomposition of the U.S. baby boom and subsequent baby bust. From a low point in the mid-1930s to its peak in 1957, the TFR increased from2.15 to 3.68. Column one shows that somewhat less than half (42%) of this birth increase can be attributed to changes in the quantum component; the remainder can be accounted for by timing shifts toward younger ages at childbearing. Further, the quantum increases are almost entirely due to increased first and second births (88%) and the timing shifts are primarily attributed to age at first birth (78%). Such decomposition shows that earlier and pervasive parenthood accounts for the majority of the baby boom increase in the TFR. Likewise, post-1957 TFR declines were driven by timing changes, in this case toward later ages of childbearing, with rising age at first birth the most important component. Post-1957 quantum changes did include important declines in third or higher order births.

Other decompositional demographic analysis provides important clues regarding whether explanations should center on cohort or period factors. The evidence is unequivocal: Postwar fertility trends in developed countries are largely accounted for by period shifts; in given calendar years, fertility rates show pervasive changes across ages. Stated differently, there is little evidence that birth year strongly conditions responses to current events.

Causes of the Baby Boom and Bust

Economist Richard Easterlin's explanation of the baby boom has spawned a large body of research. While Easterlin's theory yields valuable insights, empirical evidence requires substantial adjustments. In brief, in 1973 Easterlin identified shifts in relative income across generations as the primary cause of the baby boom. Specifically, those who were children during the 1930s were raised in uncertain times and in very modest economic circumstances. They reached adulthood in the economically prosperous postwar years and compared their economic circumstances favorably to those of their families of origin (i.e., they had high relative income). As a result, at young ages, baby boomers felt prepared to marry early and to have children early. Later, in a 1978 study, Easterlin stressed the role of relative cohort size in producing shifts in the economic well-being of successive generations. Those born and raised during the depression were members of small cohorts compared to those born during the baby boom. Small cohorts, in contrast to large ones, experienced relatively favorable conditions in educational and employment settings (had high relative income) and thus married and had children earlier. Easterlin's thesis had substantial intuitive appeal and could account for the earlier and more universal parenthood that characterized the baby boom. In addition, cohort size data accurately predicted the American fertility boom and bust. However, there is little evidence at the micro level that relative income is strongly associated with the timing of family formation or the number of children born. Since relative income is the key causal/behavioral mechanism in Easterlin's theory, this negative evidence is highly problematic. In addition, Easterlin's argument is clearly cohort-based while the empirical demographic

TABLE 1

evidence indicates the dominance of period change. Thus, substantial empirical evidence challenges Easterlin's theory and the scientific soundness of generalizing his arguments.

An adequate understanding of the baby boom requires a period orientation–period explanations "emphasize society-wide shifts that appear to affect all groups at the same time, as if there were something in the air that influenced everyone's lives" (Cherlin, p. 31). This something is much harder to identify precisely because multiple factors are changing across periods. Sociologist Andrew Cherlin approaches the task of explaining period trends in the United States through contrasting the social history of the 1950s and 1960s to the 1970s and 1980s. For instance, the breadwinner family, traditional gender-role ideology, and a robust economy characterized the 1950s. In this environment, marriage and childbearing occurred sooner and were within the reach of many. In contrast, the 1970s brought greater participation of women in the labor force, ideologies stressing individualism and self-actualization, and economic stagnation. Individuals responded to these period conditions in ways that suggested a common understanding of their meaning and that were not influenced by cohort-specific socialization experiences. These social histories provide plausible explanations for changes in the dynamic demo-graphic components described above and broadly characterize many Western industrialized countries in these decades. Comparative work across countries might identify the most important period factor or set of factors. However, isolating cause in a continually evolving social system poses difficult challenges; a compelling retrospective social history might be all that can be reasonably attained.

TABLE 2

Underemphasized in Cherlin's U.S. baby boom social history is the importance of new methods of contraception and more widely available abortion. In 1977 demographers Charles Westoff and Norman Ryder characterized the 1965 to 1975 period as a "contraceptive revolution." The import of effective fertility control interacts with changes in the timing of fertility described above. Compared to the baby boom, baby bust women had more effective fertility control, had children later, reached their desired family sizes at later ages, and thus were at lower risk of having unintended births for a fewer number of years. A substantial proportion of births during the baby boom can be classified as unwanted (i.e., women claimed that prior to the relevant pregnancy they preferred to have no more children), a proportion that declined during the baby bust. Thus, the effectiveness and availability of birth control contributed to the pace and magnitude of the baby bust.

Could There Be Another Baby Boom?

In the twenty-first century, economically advanced countries are very unlikely to experience sustained fertility at baby boom levels (i.e., TFR greater than2.5); in fact, it is generally expected that below-replacement fertility will prevail with occasional periods of very low (TFR less than 1.5) fertility. This forecast rests on the observed secular decline in high parity births. As noted above, high parity births played a very limited role in the baby boom fertility increases of the 1950s and 1960s, and the baby bust included an acceleration of the trend away from large–three or more children–families. The prohibitive costs of large families in developed countries, and the absence of powerful and persuasive ideologies that encourage having many children, combined with effective means of fertility control make a return to large families extremely unlikely. Instead, any future baby booms will result from the same demographic mechanisms responsible for the post–World War II baby boom: earlier family formation and nearly universal parenthood. Earlier childbearing ages and pervasive two-child families could conceivably produce a future baby boom of substantial size. But nearly universal parenthood does not seem likely in contexts in which women have substantial nonfamilial opportunities. Thus for most developed countries, the more likely future includes few large families and fairly high rates of voluntary childlessness. Baby booms are likely to be modest in size and will result primarily from changes in the timing of fertility.

See also: Cycles, Population; Fertility, Below-Replacement; Population Decline.

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