Population,projections, and policy: A cautionary perspective

Population projections depend on censuses, vital statistics and sample surveys, all of which have deficiencies that are most marked in the less developed countries (LDCs). Long-range projections by international agencies have recently undergone major revisions, while forecasts of the U.S. population have changed drastically over the past four years. The United Nations typically prepares “high,” “medium” and “low” projections. Even the high projection contains optimistic assumptions about fertility decline, while assumptions of constant or increasing fertility receive no serious attention. The paper suggests that high and constant fertility projections should receive more attention from policy makers, with medium estimates treated more as targets achievable only through considerable programmatic effort. At the same time, economic and social plans should be laid for dealing with the population sizes implied by the “high” variants.     

The Effect of Urbanization on China’s Fertility

The relationship between urbanization and fertility decline is known to be inverse in developed countries. However, the nature of this relationship in developing countries that already have relatively low fertilities is not well-understood. This study aims to illustrate how much urbanization contributed to China’s fertility decline between 1982 and 2008 and forecasts how much it can contribute to future reductions in fertility. The study examines changes in the total fertility rate (TFR) at both the national and provincial levels, given regional differences in the urbanization rate. The results show that changes in rural fertility behavior accounted for most of the decline in the national TFR between 1982 and 2008. This finding suggests that official birth control policies were instrumental in curbing China’s population growth. However, urbanization was responsible for about 22% of the decrease in TFR during this period, and its effect was especially important during the latter years (2001–2008). In most provinces, urbanization associated with a decline in provincial-level fertility. The forecasts indicate that urbanization will become the primary factor behind future declines in national fertility. Given the negative effect of urbanization on the TFR, it is possible to relax the one-child policy without having adverse implications for population growth.     

Probabilistic population projections for countries with generalized HIV/AIDS epidemics

In 2015, the United Nations (UN) issued probabilistic population projections for all countries up to 2100, by simulating future levels of total fertility and life expectancy and combining the results using a standard cohort component projection method. For the 40 countries with generalized HIV/AIDS epidemics, the mortality projections used the Spectrum/Estimation and Projection Package (EPP) model, a complex, multistate model designed for short-term projections of policy-relevant quantities for the epidemic. We propose a simpler approach that is more compatible with existing UN projection methods for other countries. Changes in life expectancy are projected probabilistically using a simple time series regression and then converted to age- and sex-specific mortality rates using model life tables designed for countries with HIV/AIDS epidemics. These are then input to the cohort component method, as for other countries. The method performed well in an out-of-sample cross-validation experiment. It gives similar short-run projections to Spectrum/EPP, while being simpler and avoiding multistate modelling.     

Declining world fertility: trends,causes, implications

This Bulletin examines the evidence that the world's fertility has declined in recent years, the factors that appear to have accounted for the decline, and the implications for fertility and population growth rates to the end of the century. On the basis of a compilation of estimates available for all nations of the world, the authors derive estimates which indicate that the world's total fertility rate dropped from 4.6 to 4.1 births per woman between 1968 and 1975, thanks largely to an earlier and more rapid and universal decline in the fertility of less developed countries (LDCs) than had been anticipated. Statistical analysis of available data suggests that the socioeconomic progress made by LDCs in this period was not great enough to account for more than a proportion of the fertility decline and that organized family planning programs were a major contributing factor. The authors' projections, which are compared to similar projections from the World Bank, the United Nations, and the U.S. Bureau of the Census, indicate that, by the year 2000, less than 1/5 of the world's population will be in the "red danger" circle of explosive population growth (2.1% or more annually); most LDCs will be in a phase of fertility decline; and many of them -- along with most now developed countries -- will be at or near replacement level of fertility. The authors warn that "our optimistic prediction is premised upon a big IF -- if (organized) family planning (in LDCs) continues. It remains imperative that all of the developed nations of the world continue their contribution to this program undiminished."     

Revolution,war and modernization: Population policy and fertility change in Iran

Fertility trends in Iran over recent decades can be plausibly related to a number of causal factors. Population policy shifts were quite marked, and were related to political upheaval and war, which influenced both official policy and popular perceptions of the nation’s need for children. A range of developmental factors were also important. The key fertility trends to be explained include the rise to an exceptionally high level in the early 1980s (a TFR of just below 7), and the speed of the subsequent decline to a TFR of about 2.7 in 1996. As well as estimating the proximate determinants of these trends, the paper sets them in their political and developmental context. Iran’s fertility trends are then compared with those of Islamic countries of North Africa and West Asia to gain additional insights into possible causal factors. An adequate explanation of fertility change in Iran needs to draw on elements of a number of theories of fertility transition.     

Case study: fertility decline in Iran

Iran has experienced one of the most successful family planning programs in the developing world, with 64 percent decline in total fertility rate (TFR) between 1986 and 2000. This paper focuses on Iranians’ unique experience with implementation of a national family planning program. Recognition of sensitive moral and ethical aspects of population issues resulted in successful collaboration of technical experts and religious leaders. Involvement of local health workers, women health volunteers and rural midwives led to great community participation. Demographic and Health Survey (DHS) data in 2000 indicated a TFR of 2.0 births per women and 74 percent contraceptive use among married women. This case study will help policy makers and researchers in Moslem countries and other developing countries with high fertility rate to consider a successful family program as a realistic concept with positive impacts on nation’s health and human development.     

Below-replacement fertility: Determinants and prospects in South Asia

Although 10 countries and two of China’s special administrative areas, totalling 1,528 million people or 44 per cent of Asia’s total population, are now characterized by fertility rates below long-term replacement levels, no such countries are yet found in South Asia. This paper first examines the characteristics of 12 Asian administrations with very low fertility at various stages of their fertility declines and then compares the findings with the present situation in three South Asian countries, Sri Lanka, India and Bangladesh. This allows a prediction of when the South Asian countries will reach replacement fertility in accord with the trends in two key criteria, the percentage of girls in secondary school and the infant mortality rate. These conclusions are then buttressed for each country by the findings of anthropological demographic research programs in which the authors were involved. The predictions are that all three countries will attain a total fertility rate of 2.1 within the next 30 years and that the UN2000 Revision of the medium population projection is plausible in that regard. However, the authors part company with the UN projection in their assessment that the nature of these societies means that they will all subsequently fall to still lower fertility levels.     

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。     

Data quality and accuracy of United Nations population projections, 1950-95

Between 1951 and 1998, the United Nations (UN) published 16 sets of population projections for the world, its major regions, and countries. This paper reports the accuracy of the projection results. I analyse the quality of the historical data used for the base populations of the projections, and for extrapolating fertility and mortality. I study also the impact this quality has had on the accuracy of the projection results. Results and assumptions for the sets of projections are compared with corresponding estimates from the UN 1998 Revision for total fertility and life expectancy at birth, total population, and the projected age structures. The report covers seven major regions (Africa, Asia, the former USSR, Europe, Northern America, Latin America, and Oceania) and the largest ten countries of the world as of 1998 (China, India, the USA, Indonesia, Brazil, Pakistan, Russia, Japan, Bangladesh, and Nigeria).     

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?     

Low fertility due to delay in -- not dearth of -- births

Population Council demographer John Bongaarts and his colleague Griffith Feeney argue that recent concern about a lack of births overlooks the fact that many women in developed countries are simply choosing to bear children later than women used to. So-called birth dearths are often caused by temporary delays in childbearing. The two demographers have designed a new way for demographers to account for the timing, or tempo, of childbearing in estimates of fertility. Their tempo-adjusted total fertility rate (TFR) allows demographers to correct skewed fertility trends, such as those leading to projections of birth dearths. The new measure provides a better indication of women's true propensity to bear children. Standard measures of fertility are distorted by changes in tempo. Such changes occur when large numbers of couples delay or accelerate their initiation of family building. The authors used historical data and theoretical arguments to validate the tempo-adjusted TFR, which improves upon the two common measures of fertility. Flaws in the TFR and the completed fertility rate (CFR) are corrected by Bongaarts and Feeney's new measure. To demonstrate their new tool, they examined the below-replacement fertility seen in recent decades in the US. By the mid-1990s, the TFR in almost every developed country had fallen below the replacement level of 2.1 births/woman, and in Italy, Spain, and Germany it fell below 1.5. If such fertility persists, declining population size, extreme population aging, and financial pressure upon social security systems may result. However, if fertility preferences hold at current levels, the very low fertility rates observed in the developed world will approach 2 children/couple.     

Ethnic population projections for the UK, 2001–2051

This paper reports on projections of the United Kingdom’s ethnic group populations for 2001–2051. For the years 2001–2007 we estimate fertility rates, survival probabilities, internal migration probabilities and international migration flows for 16 ethnic groups and 355 UK areas. We make assumptions about future component rates, probabilities and flows and feed these into our projection model. This model is a cohort-component model specified for single years of age to 100+. To handle this large state space, we employed a bi-regional model. We implement four projections: (1) a benchmark projection that uses the component inputs for 2001; (2) a trend projection where assumptions beyond 2007 are adjusted to those in the UK 2008-based National Population Projections (NPP); (3) a projection that modifies the NPP assumptions and (4) a projection that uses a different emigration assumption. The projected UK population ranges between a low of 63 millions in 2051 under the first projection to a high of 79 million in the third projection. Under all projections ethnic composition continues to change: the White British, White Irish and Black Caribbean groups experience the slowest growth and lose population share; the Other White and Mixed groups to experience relative increases in share; South Asian groups grow strongly as do the Chinese and Other Ethnic groups. The ethnic minority share of the population increases from 13% (2001) to 25% in the trend projection but to only 20% under our modified emigration projection. However, what is certain is that the UK can look forward to be becoming a more diverse nation by mid-century.     

Cohort Effects or Period Effects? Fertility Decline in South Korea in the Twentieth Century

This study examines if the Korean fertility decline is driven by long-term cohort changes or by fluctuating period changes. By using a classic age–period–cohort model, a moment decomposition method, and a new summary fertility measure—‘cross-sectional average fertility’—I show that the Korean fertility decline is primarily driven by period changes and that delayed childbearing has important consequences for the onset of fertility decline. These findings are in line with the existing literature in fertility changes such as theories of fertility transitions and sociological accounts of fertility changes in Western countries in the twentieth century. The policy implications of these findings are also discussed.     

The United Nations on World Population in 2300

The Population Division of the United Nations biennially issues detailed population estimates and projections covering the period 1950–2050. The most recent revision of these estimates and projections, the 2002 assessment, was released in February 2003. At irregular intervals, the Population Division also publishes long‐range projections. The most recent of these, covering the period up to 2150, was issued in 2000, based on the 1998 assessment. On 9 December 2003, the Population Division released the preliminary report on a new set of long‐range projections, dovetailing with the 2002 assessment, that extend over a much longer time span: up to 2300 ( http://www.un.org/esa/population/publications/longrange2/longrange2.htm ). Unlike previous long‐range projections, which, apart from China and In‐dia, were prepared for large regional groupings only, the new projections are elaborated separately for 192 countries. Given the enormous uncertainties of the character of demographic trends over such an extended period, the information content of these projections is somewhat elusive. However, they are expected to be used to provide the demographic input for long‐range models of global climate change. Long‐range population projections also serve to demonstrate the unsustainability of certain seemingly plausible assumptions as to the future course of particular demographic parameters. In the present case, for example, the high‐fertility projection, reflecting a sustained total fertility rate at the relatively modest level of 2.35, by 2300 would yield a population of some 32 billion in the countries now classified as less developed. Or, in a yet more extreme exercise 0/reductio ad absurdum, maintaining constant fertility at present rates would result in a population size of some 120 trillion in the countries now classified as least developed. Apart from the “high fertility” and “constant fertility” models just cited, the projections are calculated for three additional instructive variants: “low fertility,”“medium fertility,” and “zero growth.” Underlying each of the five variants is a single assumption on mortality change: expectation of life at birth creeping up, country‐by‐country, to a 2300 level ranging between 88 and 106 years. International migration is set at zero throughout the period 2050‐2300 in each variant. Thus the projections are unabashedly stylized and surprise‐free, providing a simple demonstration of the consequences, in terms of population size and age structure, of clearly stated assumptions on the future course of demographic variables. Reproduced below is the Executive Summary of the preliminary report on the UN long‐range projections presented to a UN technical working group on long‐range projections at its December 2003 meeting in New York and slightly revised afterward. A full final report on this topic by the Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat will be published later in 2004.     

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.     

Population Projections and Demographic Knowledge in France and Great Britain in the Postwar Period

This study examines how official national population projections—a key mechanism for the production and dissemination of demographic knowledge—contributed to differing interpretations of population and fertility trends in France and Great Britain in the decades following World War II, despite these countries' similar fertility rates during most of this period. Projections presented different visions of the demographic future in the two countries. In France, publication of multiple variants emphasized future contingency, with low variants illustrating future population decline due to prolonged below‐replacement fertility. In Britain, publication of a single variant, assuming near‐replacement‐level fertility rates, projected moderate growth. National population projections thus created divergent representations of the two countries' demographic futures: an ever‐present threat of population decline in France, and a reassuring image of stability in Britain. Two principal mechanisms that contributed to cross‐national differences in population projections—national demographic history and institutional configurations—are discussed.     

The Role of Relative Cohort Size and Relative Income in the Demographic Transition

This paper summarizes the results of other analyses by the author with regard to the importance of relative cohort size (RCS) in determining male relative income (the income of young adults relative to prime-age workers) and general patterns of economic growth, and in turn influencing fertility in the currently more-developed nations. It then goes on to demonstrate that these same effects appear to have been operating in all of the one hundred-odd nations which have experienced the fertility transition since 1950. Parameter estimates based on the experience of all 189 countries identified by the United Nations between 1950 and 1995 are used to simulate the effects on fertility of migration from Third to First World countries. This exercise suggests that we get the best of all possible outcomes with migration: population is reduced in “overcrowded” Third World nations, total world population growth is substantially reduced, and scores of children are given the opportunity of growing up with all the educational and health advantages of U.S. residents.     

基于调研数据的总和生育率发展趋势及影响因素分析——来自湖北鄂州、黄石、仙桃的调查数据

文章基于5490份有效问卷的调查数据对湖北省总和生育率（TFR）进行分析。结论表明,自1985年以来年龄别生育率下降主要原因是计生政策严格控制生育数量,而非生育行为的推迟。TFR呈现先快速下降后缓慢上升的趋势,其变化与高生育水平育龄妇女占比无关。与政策生育率变化有关。通过对湖北省总出生人数进行估算和分析,结论表明1985—2008年总和生育率对总出生人数的影响程度要大于高生育水平育龄妇女占比的影响;外推预测表明2009～2014年出生人数趋势稳定,2015年以后呈下降趋势。利用Logit模型对实际生育水平的影响因素进行分析,发现有显著影响的因素为：受访者文化程度、户口性质、出生年代、工作状态、丈夫工作状态、放宽的计生政策和奖励少生的计生政策。     

Wages and Fertility in Australia

This paper applies a simple economic model to explain short run movements in Australian fertility, abstracting from social and cultural conditions. It shows that Australian fertility can be modelled with some success using only wages and employment data, once we allow for the different effects of changes in men’s and women’s wages for the period 1966–90. The elasticity of the total fertility rate over this period is found to be negative with respect to women’s wages and positive with respect to men’s wages. As well as having the expected sign, the estimated elasticities are similar in magnitude to those for the United States over the period 1948–75.     

Is Lowest‐Low Fertility in Europe Explained by the Postponement of Childbearing?

In 2001, more than half of Europe's population lived in countries with a total fertility rate (TFR) at or below 1.3. Use of the adjusted TFR proposed by Bongaarts and Feeney, which takes into account the effects of the ongoing fertility postponement, changes the European fertility map considerably. All 27 countries analyzed had adjusted TFRs in 1995–2000 above 1.4. Thus, the “lowest‐low” fertility in Europe may be interpreted as a temporary consequence of the increasing age at motherhood. However, substantial regional differences in fertility level across Europe persist even when the differential pace of fertility postponement is taken into account. The estimated adjusted TFRs in Europe (1.63) and in the 25‐member European Union (1.71) contrast with the TFR levels of 1.40 and 1.46, respectively. These seemingly small differences have vastly different implications in terms of the potential long‐term pace of population decline.