Cohort Replacement and Homeostasis in World Population, 1950–2100

Using a simple empirical approach, we analyze world and regional‐level cohort replacement as determined by the key components of population dynamics, i.e. fertility, survival, and migration, for 1950–2010, using UN data. We define two kinds of homeostatic relationships among these components: fertility responses to mortality change (type I) and migration responses to changes in net reproduction (type II), and show that both can be observed to some degree in this period. We examine the extent of cohort replacement embodied in the medium‐variant UN population projections over 2010–2100 and consider how the international migration assumptions made in such projections would be affected by a homeostatic perspective.     

The End of the Fertility Transition in the Developed World

By the late 1990s the average period total fertility rate in the developed world had declined to 1.6, a level substantially lower than projected in the 1970s and 1980s. This article examines recent trends and patterns in fertility in the developed world with particular emphasis on the effects and implications of changes in the timing of childbearing. The main objective is to demonstrate that while fertility in these countries is indeed low, women's childbearing levels are not as low as period measures such as the total fertility rate suggest. To obtain a full understanding of the various dimensions of fertility change. several indicators are examined, including period and cohort fertility by birth order and childbearing preferences. An analysis of these indicators demonstrates that period fertility measures in many developed countries are temporarily depressed by a rise in the mean age at childbearing. The distortion of the TFR is as great as 0.4 births per woman in Italy and Spain. These effects have been present in many developed countries since the 1970s and could continue for years into the future. But tempo effects are temporary, and once the postponement of childbearing ends—as it eventually must—the corresponding fertility‐depressing effect stops, thus putting upward pressure on period fertility. Countries with very low fertility and substantial tempo effects may well experience rises in fertility in the near future if the timing of childbearing stabilizes. Even if this happens, however, it seems unlikely that fertility will rebound to the replacement level.     

Understanding stalling demographic transition in high-fertility countries: a case study of Guatemala

The debate surrounding the use of period, cohort, and tempo-adjusted measures has framed most of the recent studies evaluating the utility of macro-level fertility indicators. Period measures are susceptible to distortions, due to birth timing changes, but there is currently no universally accepted adjustment technique. Recent comparative analyses have offered some insights but only as applied to the low-fertility developed world setting. The utility of different types of measures in the high fertility context is unclear. Furthermore, regional variation in the pace of fertility transition is characteristic of many less developed countries and is rarely incorporated into macro-level analyses. The purpose of this analysis is to evaluate macro-fertility indicators at the regional and national levels in a high-fertility country, Guatemala, using the four most recent survey data sets. The results support the use of macro-level period indicators and adjusted period indicators of fertility in developing country contexts.     

New Cohort Fertility Forecasts for the Developed World: Rises,Falls, and Reversals

With period fertility having risen in many low‐fertility countries, an important emerging question is whether cohort fertility trends are also reversing. We produce new estimates of cohort fertility for 37 developed countries using a new, simple method that avoids the underestimation typical of previous approaches. Consistent with the idea that timing changes were largely responsible for the last decades' low period fertility, we find that family size has remained considerably higher than the period rates of 1.5 in many “low‐fertility” countries, averaging about 1.8 children. Our forecasts suggest that the long‐term decline in cohort fertility is flattening or reversing in many world regions previously characterized by low fertility. We document the marked increase of cohort fertility in the English‐speaking world and in Scandinavia; signs of an upward reversal in many low‐fertility countries, including Japan and Germany; and continued declines in countries such as Taiwan and Portugal. We include in our forecasts estimates of statistical uncertainty and the possible effects of the recent economic recession.     

The Baby Boom and Its Causes: What We Know and What We Need to Know

This study analyzes the timing, magnitude, and volume of the mid‐twentieth century baby boom in European and non‐European Western countries. The baby boom is found to have been especially strong in the non‐European countries, fairly strong in some European countries, and quite weak in others. While the boom has often been linked with postwar economic growth and the recuperation of births postponed during the Depression era, we argue that this is only a limited part of the story. In most cases the recovery of the birth rate started well before the end of World War II, a fact not accounted for by existing theories. We investigate the roles played by the recovery of period as well as cohort fertility, the underlying marriage boom, and the recovery of marital fertility. We identify major puzzles for future research, including the reasons for strongly declining ages at marriage and the role played by contraceptive failure in the rise of high‐parity births.     

Stages of the Demographic Transition from a Child's Perspective: Family Size,Cohort Size,and Children's Resources

This article provides a new characterization of stages of the demographic transition from the perspective of children competing for resources within families and cohorts. In Stage 1 falling mortality increases the size of both families and birth cohorts. In Stage 2 falling fertility overtakes falling mortality to reduce family size, but population momentum causes continued growth in cohort size. In Stage 3 falling fertility overtakes population momentum to produce declining cohort size. We apply our framework to census microdata for eight countries and to United Nations population projections for a larger set of countries. The results suggest that most countries spend two to three decades in Stage 2, with declining family size offset by increasing cohort size. From the perspective of children aged 9–11, many countries enter Stage 3 between 2000 and 2010. Other countries, especially in Africa, will continue to experience increasing cohort size for several more decades.     

An Italian Statement on International Migration

Increasing realization of the implications of persisting below‐replacement fertility in Europe—shrinking absolute numbers combined with a rising proportion of the elderly—is giving new salience to policy considerations regarding immigration in the countries most affected by low fertility. The recent United Nations report on “replacement migration” (see the Documents section in the June 2000 PDR) highlighted the issue through illustrative calculations showing the size of immigrant streams that would be needed for achieving specified demographic targets in selected lowfertility countries, given continuation of present fertility and mortality trends. For example, the UN report suggested that in Italy—which has one of the lowest fertility rates in the world—maintaining a constant population over time would require a net influx of some 12.6 million immigrants during the next 50 years, and maintaining a constant labor forceage population (ages 15–64) would require a net inflow of 18.6 million. Yet immigration policy in Western Europe has become increasingly restrictive during the last quartercentury, and the official policy stance that regulating immigration is strictly within the domain of a country's sovereign right has been assiduously maintained. (International treaty obligations qualify that right in the case of bona fide asylum seekers; however, the definition of that category is also subject to the discretion of the receiving countries.) Thus, although within the European Union national borders are open to EU citizens, the power of regulating immigration from outside the EU is retained by the individual countries rather than subject to EU‐wide decisions. Suggestions coming from the developing countries to follow up the 1994 International Conference on Population and Development with an intergovernmental conference on international migration and development were set aside by the potential immigrant‐receiving countries as overly contentious. A statement by the Minister of Foreign Affairs of Italy, Lamberto Dini, delivered at the 55th General Assembly of the United Nations, 13 September 2000, may be a sign of a notable shift in official approaches to immigration policy by at least one EU member state. The statement, in a departure from the practice of touching lightly upon a wide range of issues in international affairs, typical in high‐level ministerial speeches given at that UN forum, is devoted essentially to a single topic: international migration. It characterizes migration “between or within continents” as an international problem and advocates “coordinated and integrated” instruments in seeking a solution. It suggests that “today, with a declining birth rate and an aging population, Europe needs a strategy that embraces the complex process of integrating people from different regions of the world.” The rules for international migration, the statement claims, should be set in a global framework, such as provided by the United Nations. In the “age of globalization,”“a solidarity pact is needed to find the best and most effective way of balancing the supply and demand of labor.” With the omission of opening and closing ceremonial passages and a brief comment on the problem of debt relief, the statement is reproduced below.     

A model of the age patterns of births by parity in natural fertility populations

This research develops a convolution model to express the age patterns of fertility at each birth order in natural fertility populations in terms of six parameters, directly representing the proximate determinants of fertility, and a series of parity level indicators. The parity level indicators at each birth order are simply the proportions of women in a cohort who will eventually have births at each birth order it the age‐related fecundity decline is controlled. The Coale‐McNeil nuptiality model is adopted to represent the age pattern of first marriage rates and the natural fertility schedule employed in the Coale‐Trussell fertility model is incorporated to adjust age effects. The fast Fourier transform is used in solving the model numerically. It proves that the model is able to provide excellent fits to fertility for rural Chinese women in the 1950s.     

Eastern Europe: pronatalist policies and private behavior

Fertility trends in the 9 Eastern European socialist countries (Albania, Bulgaria, Czechoslovakia, German Democratic Republic, Hungary, Poland, Romania, USSR, Yugoslavia) are reviewed. Official policy in all these countries but Yugoslavia is explicitly pronatalist to varying degrees. Attention is directed to the following areas: similarities and differences; fertility trends (historical trends, post World War 2 trends, and family size); abortion trends (abortion legislation history, current legislation, abortion data, impact on birth rates, abortion seekers, health risks, and psychological aftereffects); contraceptive availability and practice; pronatal economic incentives (impact on fertility); women's position; and marriage, divorce, and sexual attitudes. The fact that fertility was generally higher in the Eastern European socialist countries than in Western Europe in the mid-1970s is credited to pronatalist measures undertaken when fertility fell or threatened to fall below replacement level (2.1 births/woman) after abortion was liberalized in all countries but Albania, following the lead of the USSR in 1955. Fertility increased where access to abortion was again restricted (mildly in Bulgaria, Czechoslovakia, and Hungary at various times, and severely in Romania in 1966) and/or economic incentives such as birth grants, paid maternity leave, family and child care allowances, and low interest loans to newlyweds were substantially increased (Bulgaria, Czechoslovakia, Hungary, and Poland to some extent, in the late 1960s and early 1970s, and the German Democratic Republic in 1976). Subsequent declines in Bulgaria, Czechoslovakia, Hungary, and Romania suggest that policy induced increases in fertility are short-lived. Couples respond to abortion restrictions by practicing more efficient contraception or resorting to illegal abortion. It is evident that the region's low birth rate is realized mainly with abortion, for withdrawal remains the primary contraceptive method in all countries but Hungary and the German Democratic Republic. It seems that cash incentives have advanced the timing of 1st and 2nd births without substantially increasing the 3rd births required to keep national fertility above replacement level. Demographic factors alone will most likely keep birth rates low in several Eastern European countries during the 1980s and the 1990s. Due to the low birth rates in the 1960s, there will be fewer women in the prime childbearing ages of 20-29 in at least Poland, Czechoslovakia, Bulgaria, and Hungary. It becomes clear that policy efforts to influence private reproductive behavior can only be moderately successful if the living conditions are such that women are determined not to have more than 1 or 2 children.     

Sweden faces zero population growth

In this discussion of Sweden as it approaches zero population growth, focus is on the following: population growth in perspective, fertility trends (childbearing concentrated and cohort versus period fertility), marital status (non-marital cohabitation, out-of-wedlock births, and divorce), women's changing status (increasing education and increasing employment), constraints and supports for women's dual role (family allowances and housing), birth control (contraceptive methods and practice and abortion), mortality trends, changing age structure and the elderly (average population age and proportion of elderly and cost of elderly support), international migration (from emigration to immigration and demographic impact of immigration), immigration policy, recent population debate (immigration issues and facing zero population growth). Since 1900 the primary features of Sweden's demographic history are a continuing decline in the birth rate to very low levels -- relieved by some upward movement in the 1940s and 1960s -- and a marked shift in the migration balance from emigration to immigration. It is almost entirely because of immigration that Sweden's population growth rate has not yet turned negative. If Swedish women were to continue to bear children at the rate that all women in the reproductive ages actually did in 1978, each women would end up with an average well below the level necessary to exactly replace each adult in the population leaving migration out, an annual total fertility rate of 2.1 children per woman would have to be sustained for births and deaths to be in balance under the low mortality conditions prevaling in Sweden.     

Statistical modeling of selected aspects of the childbearing process with application to world fertility survey countries∗

The childbearing process should be monitored in developing countries experiencing high population growth rates and high levels of maternal and infant mortality. A mathematical model for estimation of certain aspects of the childbearing process, which requires only data on age‐specific fertility rates, is developed. Synthetic maternal childbearing indices, namely, mean ages at first and last birth, length of reproductive life span, inter‐birth spacing, and proportion of childless women, in addition to the well‐known mean age at childbearing, for the WFS countries are obtained using the proposed model. The indices are free from age truncation effects, and, under certain assumptions, provide information about a cohort's completed fertility before the women stop reproducing. The effects of women's residence and education on fertility are also examined.     

Another Child? Fertility Ideals,Resources and Opportunities

Low fertility in most developed countries has prompted policy concern in relation to labour market supply, pensions, and expenditure on health and welfare services as well as policy debate about both the cost of children and the opportunity costs of parenthood. The extent to which family policy interventions can be effective in slowing or reversing fertility decline is much debated. This paper, based on a fertility module of the Scottish Social Attitudes Survey 2005, examines the current fertility, and ideal and expected fertility of a nationally representative sample of 455 parents of reproductive age and focuses on whether they plan to have another child. It compares the characteristics of those who intend to have another child with those who do not, and how parents with one child differ from those with more children. It addresses three questions about family size: (1) fertility ideals, (2) resources and the economic implications of childbearing, and (3) opportunities for childbearing and the effects of a late start on fertility expectations. It concludes that, despite a sustained period of low fertility in Scotland, childbearing ideals are robust and explanations of low fertility must derive from difficulties in realising those ideals. Difficulties in realising fertility aspirations are associated less with resources than with opportunities for childbearing, especially the timing of first birth. Those who delay their first birth are less likely to realise their ideal family size, and their lower fertility is associated with the opportunity costs of childbearing in terms of foregone qualifications, careers and earnings.     

Explanations of the fertility crisis in modern societies: A search for commonalities

Near‐global fertility decline began in the 1960s, and from the 1980s an increasing number of European countries and some Asian ones achieved very low fertility (total fertility below 1.5) with little likelihood of completed cohort fertility reaching replacement level. Earlier theory aiming at explaining this phenomenon stressed the incompatibility between post‐industrial society and behaviour necessary for population replacement. Recent theory has been more specific, often concentrating on the current Italian or Spanish situations or on the contrast between them and the situation in either Scandinavia or the English‐speaking countries, or both. Such an approach ignores important evidence, especially that from German‐speaking populations. The models available concentrate on welfare systems and family expenses, omitting circumstances that may be unique to individual countries or longer‐term factors that may be common to all.     

China's Below‐Replacement Fertility: Recent Trends and Future Prospects

Between 1970 and 1990, China experiencoed a rapid and sharp fertility decline—from total fertility rates of approximately six births to two. The degree to which Chinese fertility has continued to fall after 1990 is controversial. We use survey data from the 1997 National Population and Reproductive Health Survey and from the 2001 Reproductive Health and Family Planning Survey to document recent trends in Chinese fertility. Our estimates provide further evidence that China's fertility is well below‐replacement level at the turn of the twenty‐first century—with TFR levels of approximately 1.5 children per woman. Trends in parity‐specific cohort fertility by age also suggest below replacement completed fertility for cohorts still in the childbearing years. In the article's second section, we identify key components of low period fertility in order to frame our discussion of two questions: 1) in what ways is Chinese low fertility different from/similar to that in other low‐fertility countries? And 2) what are the likely future trends in Chinese fertility?     

生育率演变的生态学逻辑及人口增长的长期趋势

人口增长的长期过程一直是充满困惑与引发争论的话题,将人类复归到生态系统的普通成员,按照生态学逻辑构建一个由替代生育率内生引导、人口容量外生制约的人口增长新模型,以代替用具体社会经济因子解释短周期人口变动的传统思路,探讨生育率转变的一般模式及人口发展的长期趋势。工业革命以来,全球人口已经或正在经历着第一次、第二次生育率转变,全球生育率演变可以聚类为欧美、亚非拉、撒哈拉以南非洲和东亚四种区域模式;在计划生育政策的推动下,我国在短短的三十年内完整经历了两次生育率转变。极限替代生育率是生育率演变的长期目标,但当前已有一些国家跌破更替水平,这也许会成为各个国家的普遍经历,预示着人口容量约束的日益显性化;世界及主要国家的人口规模正在日益逼近其容量极限,并会在惯性驱动下突破容量限制,达到峰值后再以负增长方式趋近人口容量,同期的生育率也将向极限替代生育率递增复归。按趋势模拟世界和中国的可持续人口容量分别约为65亿人和12亿人。研究设计出测量人口增长惯性的新指标——人口增长惯性系数,它是生育率与实时替代生育率之比或出生率与死亡率之比,相比常用的人口惯性因子更为简便易行。     

Timing effects and the interpretation of period fertility

Low fertility levels and later childbearing in many developed countries have reinvigorated the debate between period and cohort perspectives on fertility and on the meaningfulness of the period total fertility rate (TFR). Here, fertility-timing effects are defined as level changes in period fertility that do not reflect level changes in the completed fertility of cohorts. That definition leads to the average cohort fertility (ACF) as a measure of period fertility adjusted for timing effects. In an influential paper, Bongaarts and Feeney (1998) presented an alternative approach and a different measure, TFR*, to adjust for timing effects. Here, the two measures are compared. In the context of model populations, the ACF performs well, reflecting an average of the fertility of the active cohorts. The Bongaarts-Feeney TFR*, however, is frequently unreliable and can be erratic when there are cycles in period timing. When applied to twentieth-century U.S. experience, the TFR* behaves like a period measure and yields adjustments that are often wide of the mark. The ACF shows the stability associated with cohort measures and quantifies the substantial impact that timing effects had during the "birth dearth" of the 1970s. The period TFR reached a low of 1.74 in 1976, but the ACF never went below 2.06 during the 1970s.     

Stabilization,birth waves,and the surge in the elderly*

Substantial regularities characterize the transition to stability that follows a shift from one set of vital rates to another. The new vital, rates interact with the population's initial age composition and generate birth waves whose amplitude and attenuation depend on the ratio of ultimate to initial growth and on the new pattern of stable net maternity. A greater change in growth and a later stable net maternity pattern produce larger fluctuations in the number of births. Stabilization begins at the youngest ages and proceeds upward. Sixty years after the shift, the birth waves have largely disappeared and the proportion under age 15 approximates the stable level implied by the new rates. Those patterns are manifest in the stabilization of both observed and Coale‐Demeny model stable populations.

When fertility falls, the new stable population has a larger fraction at all ages above (approximately) 30, with greater changes characterizing the extremes of life. Fifteen years after the fall, there is a trough in the number at ages 0–14. Sixty years after the fall, when the largest pre‐decline cohort is age 60–74 and the smallest post‐decline cohort is age 45–59, there is a surge in the relative size of the elderly population. Thus after two generations, the birth waves produced by a rapid decline in fertility accentuate the effects of population aging.     

流迁人口对广东省人口发展的替代效应

所谓替代迁移是指迁移人口对长期处于更替生育水平以下的人口,因人口自然减少而产生的替代效用。广东省不但是全国人口流动和迁移最活跃的省份,而且人口总和生育率已连续10年低于更替水平,进入低生育水平时期。本文实证分析广东省在无流动人口、保持峰值人口、维持峰值劳动年龄人口和潜在供养比最大值等条件下,流迁人口对总人口规模和结构的替代效应,认为适度替代流迁人口是解决长期维持低生育水平地区所产生的人口问题的有效途径。     

A demographic explanation for the recent rise in European fertility

Between 1998 and 2008 European countries experienced the first continent-wide increase in the period total fertility rate (TFR) since the 1960s. After discussing period and cohort influences on fertility trends, we examine the role of tempo distortions of period fertility and different methods for removing them. We highlight the usefulness of a new indicator: the tempo- and parity-adjusted total fertility rate (TFRp*). This variant of the adjusted total fertility rate proposed by Bongaarts and Feeney also controls for the parity composition of the female population and provides more stable values than the indicators proposed in the past. Finally, we estimate levels and trends in tempo and parity distribution distortions in selected countries in Europe. Our analysis of period and cohort fertility indicators in the Czech Republic, Netherlands, Spain, and Sweden shows that the new adjusted measure gives a remarkable fit with the completed fertility of women in prime childbearing years in a given period, which suggests that it provides an accurate adjustment for tempo and parity composition distortions. Using an expanded dataset for ten countries, we demonstrate that adjusted fertility as measured by TFRp* remained nearly stable since the late 1990s. This finding implies that the recent upturns in the period TFR in Europe are largely explained by a decline in the pace of fertility postponement. Other tempo-adjusted fertility indicators have not indicated such a large role for the diminishing tempo effect in these TFR upturns. As countries proceed through their postponement transitions, tempo effects will decline further and eventually disappear, thus putting continued upward pressure on period fertility. However, such an upward trend may be obscured for a few years by the effects of economic recession.     

Men’s Migration and Women’s Fertility in Rural Mozambique

Labor migration profoundly affects households throughout rural Africa. This study looks at how men’s labor migration influences marital fertility in a context where such migration has been massive while its economic returns are increasingly uncertain. Using data from a survey of married women in southern Mozambique, we start with an event-history analysis of birth rates among women married to migrants and those married to nonmigrants. The model detects a lower birth rate among migrants’ wives, which tends to be partially compensated for by an increased birth rate upon cessation of migration. An analysis of women’s lifetime fertility shows that it decreases as the time spent in migration by their husbands accrues. When we compare reproductive intentions stated by respondents with migrant and nonmigrant husbands, we find that migrants’ wives are more likely to want another child regardless of the number of living children, but the difference is significant only for women who see migration as economically benefiting their households. Yet, such women are also significantly more likely to use modern contraception than other women. We interpret these results in light of the debate on enhancing versus disrupting effects of labor migration on families and households in contemporary developing settings.