Modeling momentum in gradual demographic

The analysis of population momentum following a gradual decline in fertility to replacement level provides valuable insights into prospects for future population growth. Here, we extend recent work in the area by applying a new form of the quadratic hyperstable (QH) model, which relates exponentially changing fertility to the resultant exponentiated quadratic birth sequence. Modeling gradual transitions from an initial stable population to an ultimate stationary population indicates that such declines in fertility increase momentum by a product of two factors. The first factor is a previously noted continuation of stable growth for half the period of decline. The second is a not previously appreciated offsetting factor that reflects the interaction between the decline in fertility, the changing age pattern of fertility, and the changing age composition of the population. Numerical examples using both hypothetical and actual populations demonstrate that for declines of any length, the product of the two factors yields momentum values that closely agree with the results of population projections. The QH model can examine monotonic transitions between any two sets of constant vital rates. As a generalization of the fixed-rate stable model, it has great potential value in numerous areas of demographic analysis.     

What predicts breast cancer rates? Testing hypotheses of the demographic and nutrition transitions

Modern demographic and nutritional transitions have been implicated in global epidemiological transitions intensifying over the last 60 years. These transitions include steadily declining fertility rates, improving nutritional indicators, and increasing incidence rates of chronic diseases such as breast cancer. This research draws on the well established pathways linking individual reproductive and nutritional profiles to breast cancer risk, in order to test the links among demographic, nutritional, and epidemiological transitions on a global scale. We propose two hypotheses that test the reproductive and nutritional pathways that are suggested to increase breast cancer risk at the population level. We use total fertility rate (TFR) to test the reproductive behaviour hypothesis, and we use average height and the percentage of the population that is overweight for the nutritional hypothesis; these indicators are compared to breast cancer incidence rates for 2008. Accounting for national wealth and expenditures on healthcare, we found that both hypotheses were significantly associated with breast cancer incidence, although TFR appears to have a more consistent association with incidence. Drawing on our regression model, we explain trends in breast cancer incidence in selected countries, as well as making predictions about shifting breast cancer incidence rates over the next several decades. These data suggest that greater attention should be paid to the unintended health consequences of transitions that are largely considered to bring improvements in quality of life. Our findings suggest that greater investments in screening and treatment are particularly needed in regions undergoing transitions in fertility rates, particularly those areas experiencing super-low fertility.     

A new method for estimating the level of natural fertility in populations practicing birth control

The natural fertility schedule of a population is the schedule of age-specific marital fertility we would observe if no birth control were being practiced. In natural fertility (no birth control) populations we can observe the natural fertility schedule directly, but in populations practicing birth control the natural fertility schedule is disguised by the marital fertility rates in those age intervals in which control is exercised, the marital fertility rates being below the natural rates. This paper elaborates a method for estimating the natural fertility schedules of populations practicing birth control. Two alternative models are presented, one nonlinear and one linear. The use of these models is then illustrated with reference to the Old Order Amish population of Lancaster County, Pennsylvania. It is shown that for Amish women born between 1860 and 1900 both the nonlinear and linear models yield an estimate of .843 as the ratio between Amish and Hutterite natural fertility schedules.     

Some aspects of mating and fertility in the West Indies

This paper deals with certain problems in fertility analysis in the West Indies that have their origin in two characteristics of the populations involved: the diversity of family forms and the imbalance between the sexes. Considerations of the main features of these family types, in terms of a fourfold classification as well as in terms of the threefold classification adopted at recent censuses (single, common law and married), show that many techniques relied on in the study of fertility among European populations are inapplicable to West Indian populations.

The limited data available permit only rough estimates of the rates of formation of different types of unions: but these emphasise that formal marriage usually takes place late in the childbearing period, generally after the couple has had one-or more children, that the formation of keeper unions begins considerably earlier and that the common law type is a transitional state between the looser keeper union and the state of formal marriage.

There seems to be no chance of studying fertility differentials among the several family types in terms of reproduction rates. Census data however provide three measures for this purpose, all of which show that fertility is highest for the married type and lowest for the single or keeper union. These differentials seem to run counter to the more usual pattern of fertility differentials which show fertility lowest among groups of high socio-economic standing.

Imbalance between the sexes is of importance primarily in the problem of arriving at satisfactory indices of fertility, though it may also have contributed somewhat to the establishment of the pattern of low marriage rates. Wide discrepancies between rates based on males and rates based on females appear, both in respect of fertility levels at given points of time and in respect of fertility trends. These discrepancies seem closely related to the imbalance between the sexes in. the reproductive age span. Under these conditions the use of joint G.R.B's clearly offers a more realistic measure of fertility than rates based on either sex.     

Birth delays skew developing world's fertility figures

This article explains that birth delays skew developing world's fertility figures. When successive groups of women who have delayed childbearing start having children, the rapid fertility decline stalls. Such change in the timing of childbearing skews the total fertility rate (TFR). Analysis of the tempo component of TFR trends in Taiwan suggests that tempo effects reduced its TFR by about 10% in the late 1970s and early 1990s and by about 19% in the late 1980s. In Colombia, on the basis of increasing mean maternal age at childbirth between the 1970s and the late 1980s, tempo distortions of the TFR during the most of the 1980s seem likely. Moreover, many developing countries are now experiencing rapid fertility declines that are in part attributable to tempo changes. These changes have accelerated past fertility transitions, but they also make these countries vulnerable to future stalls in fertility when the delays in childbearing end. Since fertility reductions caused by tempo effects lead to real declines in birth rates and hence in population growth, countries that wish to reduce birth rates can take actions that encourage women to delay marriage and the onset of childbearing.     

Socio-economic status and fertility decline: Insights from historical transitions in Europe and North America

The timings of historical fertility transitions in different regions are well understood by demographers, but much less is known regarding their specific features and causes. In the study reported in this paper, we used longitudinal micro-level data for five local populations in Europe and North America to analyse the relationship between socio-economic status and fertility during the fertility transition. Using comparable analytical models and class schemes for each population, we examined the changing socio-economic differences in marital fertility and related these to common theories on fertility behaviour. Our results do not provide support for the hypothesis of universally high fertility among the upper classes in pre-transitional society, but do support the idea that the upper classes acted as forerunners by reducing their fertility before other groups. Farmers and unskilled workers were the latest to start limiting their fertility. Apart from these similarities, patterns of class differences in fertility varied significantly between populations.     

Developing strategies for deriving small population fertility rates

Many agencies require population estimates and projections by ethnic group. These projections need ethnic-specific, age-specific fertility rates (ASFRs) but their inclusion is challenging since ethnicity is not recorded at birth registration. In this paper maternity data are used in a case study of electoral wards in Bradford, West Yorkshire, to develop fertility rates for small populations for a 1991 based projection. The challenge is to capture local variations in fertility by ethnic group when data are sparse. Small areas were grouped together using cluster analysis to define combinations with similar sociodemographic and fertility experiences so that sparse data could be aggregated to estimate reliable ethnic-specific fertility rates. For comparison, the data were aggregated into the 1991 Office for National Statistics area type classification. Fertility rates by single year of age for all area types were smoothed using the Hadwiger function. For the White ethnic group there were sufficient births to create ethnic-specific, ward-level ASFRs. For other ethnicities grouping of areas was necessary. The accuracy of the ASFRs in predicting births was assessed using mean absolute percentage error. Results show that for some minority groups district-level ethnic-specific fertility rates produced the most accurate birth estimates even though they were based on a larger area. This implies that rates created may be informative about the local area for White ethnic type but not in the same way for smaller ethnic groups. In terms of grouping strategies we recommend that existing classifications are assessed to determine how well variations in rates are stratified before embarking on a custom scheme. Where population sub-groups are small in some areas, it may be more reliable to use rates derived for larger areas and apply these to local populations. Inevitably, the rates used in a projection are a compromise but hopefully will still capture important dimensions of population change.     

Calculation of age-specific fertility schedules from tabulations of parity in two censuses

The mathematics of stable populations recently has been generalized to cover populations with time-varying fertility and mortality by a modification incorporating the sum of age-varying growth rates in place of the fixed growth rate of a stable population. Equations that characterize nonstable populations apply to any cohort-like phenomenon with a measurable property that cumulates gains or losses through time. In particular, the equations fit the relation between a population's average parity at a given age and age-specific fertility rates previously experienced at lower ages. Techniques devised to derive an intercensal life table from single-year age distributions in two censuses are adapted to estimate accurate intercensal fertility schedules from distributions of parity by age of woman in two censuses. Birth-order specific fertility schedules are also estimated.     

Fraught with Ambivalence: Reproductive Intentions and Contraceptive Choices in a Sub-Saharan Fertility Transition

Demographic studies that search for signs of fertility transition in sub-Saharan Africa rarely examine the complex gamut of individual aspirations and misgivings, hopes and frustrations, failures and triumphs that accompany the emerging declines of fertility rates in the subcontinent. This study draws upon qualitative data collected in peri-urban areas of Maputo, Mozambique’s capital and largest metropolis, to explore contradictory meanings and feelings surrounding changes in fertility intentions and contraceptive choices. It argues that although changes in these two aspects of reproductive life are interrelated, they are predicated on distinct types and configurations of external pressures and psychological apparatus, which is often manifested as a puzzling disjunction between fertility preferences and contraceptive use. This disjunction can be further reinforced by persistent gender divisions in reproductive views and strategies. Informal social interaction plays an important role in building societal consensus over fertility matters, but because such interaction deals with reproductive intentions and contraceptive use through largely different mechanisms, it may also help accentuate the intentions-contraception disjunction. This study’s findings therefore call upon both researchers and policymakers to attend more closely to the multidimensionality of fertility transitions in sub-Saharan societies and specifically to the complexities underlying such popular notions as “unmet need for family planning,” “spacing” versus “limiting” births, or “spousal communication” on reproductive matters.     

Economic structure and fertility: A comparative analysis

This study empirically investigates the relationship between the economic structure of populations and their level of fertility, using data from censuses recently conducted in some 50 nations. Findings show that high rates of female labor force participation outside the home and low rates of economic activity of children depress a society’s fertility level, as measured by the crude birth rate or the child-woman ratio. It is also hypothesized, but not confirmed, that the per cent of unpaid family workers in a society is positively related to its fertility level. A model is presented that treats these three components of economic structure as intervening variables through which the exogenous variables, urbanization, industrialization, and education, operate in influencing the fertility level of a society.     

Rethinking the effectiveness of family planning in Africa

For the past 50 years there has been a near global consensus that the demands of development necessitate that couples reduce their fertility as a critical act which would jump start economic growth. This consensus heralded the era of the One Child policy and over 90% of least developed states continue to run programs which seek to induce lower fertility rates in their populations. However, a growing body of literature is questioning both the validity and utility of these interventions. This article seeks to contribute to the rethinking of family planning programs. Using new data on family planning scores from forty two African states this article shows that rates of fertility are unlikely to be affected by the strength of family planning programs at lower levels of development. However, at moderate levels of development, family planning programs may contribute to accelerating the decline in fertility initiated by exogenous factors. These findings offer a fresh perspective on the wide spread adoption of family planning policy that permeates the developing world.     

China's demographic dilemmas

The year 2000 marks the end of a tumultuous century in China's population history, which weathered the demographic effects of devastating famines, wars, and epidemics and population growth and change. This paper examines the effect of population policies on the demographic dilemmas of China. In the 1950s, China had seen the fastest demographic transition in history, with a dramatic decline in mortality rates, followed by a decrease in fertility rates. However, in the 1970s, revisions in population control measures, changes in age structure, and fluctuations in age at marriage resulted in lower fertility rates. The struggles encountered by China in regulating fertility are described; these include the different methods of birth control, gender preference, marriage, population aging, and minority populations. Population and development issues within the context of urbanization, employment, education, health care, economy, and environment are also discussed. Future implications of these findings indicate the need for a systematic, effective, and complete environmental clean-up, as well as fertility and population policies.     

Demographic responses and demographic transitions: A case study of sweden

An important study by Friedlander investigated some of the effects of different demographic responses on national demographic transitions. England and Sweden were advanced as cases that approximated the suggested hypothetical models of transitions. His argument implied that the rural population of a country (in this case Sweden) experiencing mortality decline but little industrialization would reduce its fertility rates if out-migration from agricultural areas were not possible. This present study, using more complete data and better measures, concludes that this did not occur in Sweden—it did not conform to Friedlander’s hypothesized model. Because the potential implications of these findings could be profound and wide-ranging, there is a need for more studies of individual countries using better data and giving more careful attention to Davis’s theory on which the Friedlander hypothesis is based.     

Immigration to the UK from High‐Fertility Countries: Intergenerational Adaptation and Fertility Convergence

The fertility of immigrants' children increasingly shapes the ethnic diversity of the population in Western Europe. However, few data are available on the fertility patterns of immigrants and their offspring. This article provides new fertility estimates of immigrants and immigrants' children by ethnic group in the United Kingdom that may provide better‐informed fertility assumptions for future population projection models. The impact of migration‐specific tempo effects on the period TFR of immigrants is analyzed. Among the results, intergenerational fertility transitions strongly contribute both to fertility convergence between ethnic groups and to fertility “assimilation” or “intergenerational adaptation” to the UK mainstream childbearing behavior. Ethnic fertility convergence, particularly marked for populations originating from high‐fertility countries, reflects in part decreasing fertility in sending countries and in part intergenerational adaptation to the UK mainstream. Higher educational enrollment of the daughters of immigrants may partly explain their relatively lower fertility.     

The contribution of HIV to fertility decline in rural Zimbabwe, 1985-2000

HIV-related sub-fertility has been reported for those populations in sub-Saharan Africa in which contraceptive use is low. We use data from a retrospective survey in rural Zimbabwe and multivariate logistic regression models to show that recent birth rates and current pregnancy rates are also lower among HIV-positive women than among HIV-negative women in those African populations where contraceptive use is high. The fertility reduction is smaller than where contraceptive use is low because age at first sexual intercourse is later and birth rates at older ages are already low. Nevertheless, total fertility is approximately 8.5 per cent lower and HIV-associated sub-fertility may account for as much as one-quarter of fertility decline in Zimbabwe since the late 1980s. Mechanisms for HIV-associated sub-fertility in rural Zimbabwe include more frequent widowhood and divorce, reduced coital frequency, increased amenorrhoea, and possibly, pelvic inflammatory disease. Miscarriage appears to be a less important factor than elsewhere possibly because syphilis is rare.     

Explaining fertility transitions

In this essay. I suggest that the crisis in our understanding of fertility transitions is more apparent than real. Although most existing theories of fertility transition have been partially or wholly discredited, this reflects a tendency to assume that all fertility transitions share one or two causes, to ignore mortality decline as a precondition for fertility decline, to assume that pretransitional fertility is wholly governed by social constraints rather than by individual decision-making. and to test ideas on a decadal time scale. I end the essay by suggesting a perceptual. interactive approach to explaining fertility transitions that is closely allied to existing theories but focuses on conditions that lead couples to switch from postnatal to prenatal controls on family size.     

Divergent Patterns in the Ethnic Transformation of Societies

The uneven timing of the demographic transition in different countries of the world will lead to divergence between countries in ethnic and religious homogeneity. Developed‐country populations that began their fertility transitions relatively early are becoming increasingly diverse with respect to the ethnic origin and religion of their inhabitants, primarily as a result of high recent levels of immigration. Many demographic patterns of the developed world, such as low death and birth rates, are becoming universal. It might be expected that less developed countries will also turn from emigration to experiencing immigration, as their populations age and their economies develop. This essay suggests, however, that future ethnic diversity arising from immigration may be less marked in many of those developing countries than in the West, especially among latecomers to the fertility transition. Five reasons are advanced as impediments to the globalization of ethnic heterogeneity arising from immigration: demographic, economic, political, and factors related to resource constraints, and climate change. The essay considers what social, economic, and political consequences might arise if high levels of ethnic diversity, and possibly ethnic replacement, remained an idiosyncratic peculiarity of today's developed countries, which would therefore diverge in important ways from the rest of the world as the twenty‐first century unfolds.     

Closing a Sociodemographic Chapter of Chinese History

At its recent Fifth Plenary Session held in Beijing, the Eighteenth Central Committee of the Communist Party of China decided to abolish the one‐child policy and allow all couples to have two children, thus closing an important chapter of China's social and demographic history. Recent fertility trends make it clear why it is urgent to abandon this policy. Census and survey data show that China's TFR had already fallen below replacement in 1991. Since the mid‐1990s, TFRs in most years have been lower than 1.5 children per woman. Since 2010, even lower fertility rates have been recorded by the annual population change surveys. Since the mid‐1990s, fertility decline has been increasingly driven by generalized ideational changes resulting from the social, economic, and cultural transformation of recent decades. In recent years many couples who were entitled to have a second child have chosen not to do so. For this reason, the termination of the one‐child policy is unlikely to lead to a major upturn in fertility, but rather to the continuation of a low‐fertility regime with more diverse fertility patterns across different sub‐populations, a pattern that has been observed in many countries.     

A method of estimating the time of marital fertility decline and associated parameters

Significant research attention has been given to historical patterns of marital fertility transitions in currently industrialized countries. Specifically, studies consider the time of the onset of fertility decline and its distribution among populations or population subgroups; the distribution of pre-decline parital fertility levels; and/or the rate of marital fertility decline. Analyses of pre-decline fertility level and its rate of decline, however, depend upon the procedure used to estimate the time of fertility decline. The Princeton European Fertility Project is the most prominent historical fertility study ever conducted. The procedure employed to estimate the timing parameter in these Princeton studies is described. An alternative statistical procedure is then proposed for detecting the onset of the transition from high to low marital fertility; the method may also be used to find the termination point of decline where the sequence of fertility variables is long enough. Both methods produce maximum likelihood least squares estimates, but the form proposed in the text has conceptual advantages.     

Patterns underlying fertility schedules: A decomposition by both age and marriage duration

Summary Model fertility schedules based on the proportions married and the age pattern of marital fertility are unsatisfactory to the extent that marital fertility does not depend on age alone but also on other factors. Most notably, models based just on age fail to allow for differences between populations in their composition by marriage duration. Examination of the major series of fertility rates specific by both age and duration of marriage (Sweden 1911-70, England and Wales, 1941-70) reveals striking underlying regularities. The marital fertility rates observed at any given point in time can be factored into three independent components - an overall level, a vector of age effects common to all marriage durations and a vector of duration effects common to all age groups. A simple product of these three components is shown to approximate the data very closely over the entire series, despite major changes in the aggregate levels of fertility and nuptiality during the periods concerned. Not only are the data tightly structured, conforming very closely to this simple multiplicative model, but the vectors of age and duration effects themselves are shown to exhibit clear and meaningful regularities.