Theories to Explain Fertility Changes

Demographers have struggled to explain differences among countries in the timing and speed of such fertility changes as well as how prior mortality declines, socioeconomic changes, organized family planning programs, and the diffusion of various norms and ideals related to childbearing contribute to these differences. The ''theory of demographic transition" has become the overriding paradigm to explain how fertility changes. Demographic transition describes the societal shift from high fertility and high mortality (pre-transition) to low fertility and low mortality (post-transition). According to the classic demographic literature, demographic transition is caused by socioeconomic development and modernization. In addition, a decline in mortality precedes the drop in fertility (Notestein, 1945, 1953). The empirical record, however, appears to refute the simplest statements of demographic transition theory. For example, changes in reproductive behavior often have only been loosely correlated with economic, social, or cultural change, which tend to occur at different paces (Cleland, 1985). In Thailand, for example, Knodel and colleagues (1987) document how change in reproductive behavior and attitudes permeated almost every segment of Thai society within a period of approximately 15 years. The Committee on Population documents how changes in fertility and contraceptive use in Kenya cut across social, economic, ethnic, and geographic boundaries (Brass and Jolly, 1993).

The inability of demographic transition theory to accurately predict the timing or pace of actual fertility transitions has generated debate about the relative importance of a set of factors that contribute to fertility decline within particular structural or cultural contexts. Fertility declines are undoubtedly linked to social, economic, political, and cultural changes, but the nature and specific combination of each of these factors varies from one society to another.

The growing frustration within the field at the lack of predictive power of demographic transition theory has been the catalyst for researchers to reexamine the contribution of diffusion theory to the determination of the timing and pace of fertility transition. The essential idea behind diffusion theory is that social interaction is a key mechanism through which the adoption of new technologies, ideas, and behaviors takes place. However, there are many different views on how diffusion should be defined, as explained in this report.

In the late 1970s and early 1980s, diffusion theory attracted the interest of several demographers as evidence mounted that theories relying on individual rational decision making in response to economic or structural change could not fully explain the observed fertility transitions in many areas of the world. While both mortality declines and structural and economic changes remain important elements of explanations for fertility declines, the results of two major research efforts completed in the mid-1980s—the Princeton European Fertility Project and the World Fertility Survey—caused certain researchers to conclude that structural and economic changes alone provide an incomplete explanation (see Bongaarts and Watkins, 1996; Cleland and Wilson, 1987; Coale and Watkins, 1986).

Some researchers viewed the findings of the Princeton European Fertility Project as providing major support for diffusion theory explanations of fertility change (Knodel and van de Walle, 1979). This project analyzed aggregate historical demographic data from the time of the fertility transition in Europe (approximately 1880 to 1930) for many of the provinces in that region (Coale and Watkins, 1986). Lesthaeghe's (1977) volume on Belgium is one of the studies that illustrated the limitations of strictly economic theories of the timing and pace of fertility change. Several interpretations of the European evidence concluded that diffusion processes were major determinants of the observed patterns of change. Knodel and van de Walle (1979) were among the first to endorse diffusion theories in their interpretive review of findings from fertility research in the 1960s and 1970s. Support for the diffusion theory was again articulated by Watkins (1986) and later augmented with theory about the micro-level social mechanisms that generate aggregate-level patterns of fertility change (Watkins, 1990).

The World Fertility Survey (WFS) was based on cross-sectional surveys of women in developing countries, and it found similar patterns for regions outside Europe. Diffusion theories gained new credibility and were perceived as challenging purely economic theories of fertility change (Cleland and Wilson, 1987). Cleland (1985:247), for example, noted: "The fact that parental education and cultural factors, denoted by language, ethnicity, or region, emerge as major independent determinants of the onset of decline is more consistent with ideational than structural theories."

Findings from these two major research projects prompted attempts to articulate how diffusion processes affect the timing and pace of fertility change. In an influential and controversial piece, Cleland and Wilson (1987) argued that diffusion processes are key to understanding both historical and contemporary fertility transitions. More recently, Kirk (1996) and Van de Kaa (1996) reviewed theory and research on fertility over the past five decades and attempted to place diffusion arguments in this larger context. Finally, Mason (1997) also specified "social interaction and influence" as a key mediating factor in a larger framework for fertility transition.

In addition, several researchers have recently published empirical evidence that diffusion dynamics have affected fertility change in developing countries. Bongaarts and Watkins (1996) combined analysis of national-level data with qualitative material from Kenya. Entwisle et al. (1996) blended survey and qualitative interview data in a study of contraceptive method choice that revealed powerful diffusion effects. In an aggregate-level analysis, Montgomery and Casterline (1993) examined the diffusionist patterns of fertility change in Taiwan in the 1960s and 1970s. Finally, Rogers and Kincaid (1981) and later, Montgomery and Chung (1998) used micro-level data from Korea to investigate how social networks affect contraceptive decisions. These studies vary in their theory, methods, and data, but each one focuses on social interaction processes and their impact on the timing and pace of fertility change.

Along with the recent empirical research on diffusion effects on fertility, there has been an effort to develop behavioral models that incorporate these effects. One important concept in this area is the idea of "social learning" or acquiring information through social networks, as presented in work by Montgomery and Casterline (1996) and Kohler (1997). In addition, Rosero-Bixby and Casterline (1993) proposed that social interaction processes can be specified as feedback effects within the conventional fertility determinant frameworks of the 1970s and 1980s. Pollack and Watkins (1993) also tackled the problem of fitting social interaction effects into conventional fertility theory. Some of this recent work appears to draw on social network and communication theory developed in the 1960s and 1970s, which has been reviewed by Rogers and Kincaid (1981) and Beckman (1983).

The Workshop

There is a growing body of researchers who are interested in the contribution that diffusion theory might make to the explanation of fertility transition in developing countries. Yet the magnitude and nature of diffusion effects are still unclear. Motivated by these unresolved issues, the National Research Council convened the Workshop on Social Processes Underlying Fertility Change in Developing Countries on January 29-30, 1998, at the National Academy of Sciences in Washington, D.C.

This workshop was intended to serve as an arena for leading researchers who are working on diffusion processes and fertility change to discuss their recent theories and findings and to consider the implications that these findings may have for future research and policy endeavors. This subject is often a contentious one, and there is no single common language or body of theory that guides the debate. Therefore, the idea behind the workshop was not to reach a consensus regarding how diffusion affects fertility change, but rather to ask the leading researchers who have been working in this area to come together and provide their assessment of what is now known about the possible role of diffusion in the fertility transition.

Workshop participants represented a number of different disciplines, including demography, sociology, economics, anthropology, decision sciences, communication, public health, and population policy. The goal was to bring together these representatives of various disciplines to review current knowledge and theory about certain aspects of diffusion. Participants were asked to examine what is now known about the relationship between the diffusion of ideas and the fertility transition, to identify some of the major obstacles to increasing understanding of diffusion processes and fertility change, and to suggest how the obstacles might be overcome. Fourteen papers were presented at the workshop. These papers and the discussion at the workshop are summarized in this report.²

The workshop organizers posed five specific questions to the participants:

1.

How can diffusion be defined in the population and family planning context?

2.

Can diffusion effects be measured, and if so, how?

3.

What are the channels through which diffusion operates and how important is each channel?

4.

What do diffusion effects contribute to the explanation of fertility transitions beyond the effects of structural change?

5.

What are the public policy implications of diffusion research?

The goal of the workshop was not to achieve consensus on these questions but to delineate the issues involved, summarize what is known, highlight areas of agreement, identify key areas of disagreement that require further study, and, insofar as possible, characterize the policy and program options.

The discussion is summarized in five sections below, corresponding to these five main questions; however, this division is to some extent artificial, because the topics are so closely related. For example, it is difficult to disentangle the question of the relative role of diffusion and structural change and the question of what exactly is being diffused (e.g., information about family planning or information about the economic benefits of smaller families). Much overlap therefore occurs throughout the text that follows, as it did at the workshop.

Footnotes

1

The total fertility rate (TFR) is a period measure that represents the number of births a woman would have if she experienced age-specific birth rates throughout her reproductive years. It is the sum of these age-specific birth rates as observed in a given year (Shryock and Siegel, 1971). In Latin America and the Caribbean, for example, the TFR was 5.2 children per woman in 1970, but had declined to 2.8 by 1991. Similarly, in Southeast Asia, the TFR declined from 6.0 children per woman in 1970 to 3.5 in the mid-1990s. Only parts of sub-Saharan Africa and South Asia have registered little or no decline in fertility rates.

2

The papers were bound in draft form and distributed to a limited audience in 1998. A selection of the papers will be edited and published as a separate volume.