Population dynamics in Germany: the role of immigration and population momentum

The effects of changes in rates of mortality, fertility, and migration depend not only on the age-specific patterns and levels of these rates, but on the age structure of the population. In order to remove the influences of the age structure and concentrate on the effects of the demographic rates themselves, a common practice is to analyze the influences of the rates for a standard age structure. This paper analyzes current and future population changes in Germany, using a stationary population equivalent model (SPE) that shows long-term effects of current fertility, mortality, and international migration patterns. Results indicate that the German population will eventually decline because of below replacement fertility, if net immigration does not counteract this decrease. This means, for instance, that the long-term stationary population levels for Germany will decrease by approximately 6.5 million during a decade in which current fertility, mortality, and international migration levels prevail. The paper also reports how various other assumptions for mortality, fertility, and international migration affect the SPE model for Germany.     

Population momentum across the demographic transition

Population momentum is the main driver of global population growth today, and this makes an appreciation of momentum critical to understanding contemporary worldwide growth dynamics. This article traces population momentum along with two recently defined measures of momentum decomposed—stable and nonstable momentum—across the demographic transition. We use historical data and population projections from 16 countries to illustrate some previously ignored empirical regularities of the demographic transition in both the developed and the developing world. We also demonstrate the dynamic nature of stable and nonstable momentum, as changes in stable momentum lead to predictable changes in current and future nonstable momentum. These results suggest that momentum, which by definition is measured at a point in time, can also be considered as a process that unfolds over time.     

Population momentum: A wider definition

Summary

Keyfitz has derived an elegant formula for estimating the ultimate size of an initially stable, growing population that abruptly reduces its fertility to replacement level. Reduction of fertility is achieved by the rather unrealistic device of dividing the original age schedule nffertility rates by the net reproduction rate. Only the inertia of the age distribution is thus accounted for, but not that of the fertility schedule. The key idea of an abrupt imposition of a fixed regimen capable in the long run of generating zero population growth may be retained, but the regimen made more realistic. By elaborating the population setting, such disparate ZPG regimens as reduction of marital fertility by contraception, delayed and/or less universal marriage, raised mortality risks, or permanent net out-migration may be formulated. Convergence of the populaton to stationarity becomes a two-phase process: a primary adjustment period of changing fertility rates followed by a period of age adjustment.

The present paper treats what happens when a fixed ZPG sterilization regimen, defined by a minimum age of sterilization γ and constant continuous risk φ of sterilization among unsterilized wives aged γ to β, is imposed abruptly (or else progressively over an interval T) upon an initially stable, growing population. Additional sources of residual growth are: (1) the nine-month lag in sterilization effect owing to pregnancy: (2) the more youthful pattern of child-bearing under sterilization: (3) the extra adjustment period (of length β-γ-0.75) of changing fertility rates; and (4) any delays in exposing elements of the population to the sterilization regimen.

Two questions are pursued. First, how important are the additional sources of residual growth? Secondly, how do their relative sizes vary as a function of the characteristics of the initial population?     

Population momentum for gradual demographic transitions

Population momentum is the ratio of a population's ultimate size after a demographic transition to its initial size before the transition. For an instantaneous drop to replacement fertility, Nathan Keyfitz found a simple expression M K for the momentum. However, as Keyfitz pointed out, `no one thinks that any country will drop immediately to stationary reproduction patterns'. We present results concerning the momentum of a population whose demographic transition is completed within a finite time. First, we provide an exact analytical formula for such a population's momentum. Second, for rapid fertility transitions, we obtain a simple exact expression for momentum that reduces to Keyfitz's M K if the transition is instantaneous. We show, by example, that our simpler formulae are accurate approximations to population momentum for transitions that take as long as 100 years. Finally, we show that the speed of fertility decline makes a substantial difference to population momentum.     

Population momentum: A wider definition

Summary Keyfitz has derived an elegant formula for estimating the ultimate size of an initially stable, growing population that abruptly reduces its fertility to replacement level. Reduction of fertility is achieved by the rather unrealistic device of dividing the original age schedule nffertility rates by the net reproduction rate. Only the inertia of the age distribution is thus accounted for, but not that of the fertility schedule. The key idea of an abrupt imposition of a fixed regimen capable in the long run of generating zero population growth may be retained, but the regimen made more realistic. By elaborating the population setting, such disparate ZPG regimens as reduction of marital fertility by contraception, delayed and/or less universal marriage, raised mortality risks, or permanent net out-migration may be formulated. Convergence of the populaton to stationarity becomes a two-phase process: a primary adjustment period of changing fertility rates followed by a period of age adjustment. The present paper treats what happens when a fixed ZPG sterilization regimen, defined by a minimum age of sterilization γ and constant continuous risk φ of sterilization among unsterilized wives aged γ to β, is imposed abruptly (or else progressively over an interval T) upon an initially stable, growing population. Additional sources of residual growth are: (1) the nine-month lag in sterilization effect owing to pregnancy: (2) the more youthful pattern of child-bearing under sterilization: (3) the extra adjustment period (of length β-γ-0.75) of changing fertility rates; and (4) any delays in exposing elements of the population to the sterilization regimen. Two questions are pursued. First, how important are the additional sources of residual growth? Secondly, how do their relative sizes vary as a function of the characteristics of the initial population?     

On the momentum of population growth

If age-specific birth rates drop immediately to the level of bare replacement the ultimate stationary number of a population will be given by (9): $$\left( {{\textstyle{{b\mathop e\limits^ \bullet {}_0} \over {r\mu }}}} \right)\left( {\frac{{R_0 - 1}}{{R_0 }}} \right)$$ multiplied by the present number, where b is the birth rate, r the rate of increase, \(\mathop e\limits^ \bullet _0 \) the expectation of life, and R ₀ the Net Reproduction Rate, all before the drop in fertility, and μ the mean age of childbearing afterwards. This expression is derived in the first place for females on the stable assumption; extension to both sexes is provided, and comparison with real populations shows the numerical error to be small where fertility has not yet started to drop. The result (9) tells how the lower limit of the ultimate population depends on parameters of the existing population, and for values typical of underdeveloped countries works out to about 1. 6. If a delay of 15 years occurs before the drop of the birth rate to replacement the population will multiply by over 2. 5 before attaining stationarity. The ultimate population actually reached will be higher insofar as death rates continue to improve. If stability cannot be assumed the ultimate stationary population is provided by the more general expression (7), which is still easier to calculate than a detailed projection.     

Population aging and endogenous economic growth

We investigate the consequences of population aging for long-run economic growth perspectives. Our framework incorporates endogenous growth models and semi-endogenous growth models as special cases. We show that (1) increases in longevity have a positive impact on per capita output growth, (2) decreases in fertility have a negative impact on per capita output growth, (3) the positive longevity effect dominates the negative fertility effect in case of the endogenous growth framework, and (4) population aging fosters long-run growth in the endogenous growth framework, while its effect depends on the relative change between fertility and mortality in the semi-endogenous growth framework.     

Population aging raises questions for policymakers

This issue of Asia-Pacific Population and Policy examines the size of the elderly population in Asia and projections for the next 50 years. It discusses some of the characteristics of Asia's elderly population. Information is based on a study of population momentum and population aging at the East-West Center prepared by the UN for the 32 countries in East, Southeast, and South Asia with populations of 150,000 or more. Demographic analysis revealed that the population aged 65 and above are projected to increase during 2000-50 by about 3% per year; of all Asians aged 55 and older, roughly one-half are now between the ages of 55 and 64, about one-third are between 65 and 74, and almost one-sixth are 75 and above. In most countries of Asia, older women are outnumbered by older men. Among the population aged 55 and above, there are about 90 men for every 100 women and among those aged 75 and above, there are only about 70 men for every 100 women. This analysis of demographic data suggests that the elderly population will expand dramatically in Asia over the next 50 years. This changing situation poses a challenge for policy makers in the provision of personal care and financial support for Asia's growing elderly population.     

Population aging and legal retirement age

This paper analyzes the effects of population aging on the preferred legal retirement age. What is revealed is the crucial role that the indirect ‘macro’ effects resulting from a change in the legal retirement age play in the optimal decision. Two social security systems are studied. Under a defined contribution scheme, aging lowers the preferred legal retirement age. However, under a defined pension scheme, the retirement age is delayed. This result shows the relevance of correctly choosing the parameter affected by the dependency ratio in the design of the social security programme.

On population aging in China

By 2040, the proportion of the elderly in China's population will be 20.9%. 3 problems that must be discussed are 1) the cost of supporting this large number of elderly people, 2) the relative decrease in the working population, and 3) the increased problems of older people. In 2040, the proportion of the working population will be 63.5% of the population, the aged will form 20.8% of the population, and children will form 15.7%. In 1982, the proportions were 61.6% working ages, 4.9% elderly, and 33.6% children. Expenditures on dependent aged people in the future will balance that on children now because elderly people do not remain consumers as long as children do and children's educations, cost more than health care for the elderly does. The standstill or decrease in the absolute number of people will lead to a stop in the growth of the absolute number of the working population. Production will then depend on the quality rather than the quantity of population. A low standard of living and backward social welfare facilities are problems in caring for the aged in China today. What is now being practiced in China in caring for the aged is a combined system of care by the individual, the collective, and the state. The overwhelming majority of the rural elderly are supported by their families, while the majority of the urban elderly are supported by the collective.     

Population momentum for gradual demographic transitions: an alternative approach

In this article, I derive a simple formula for approximating the ultimate size of a population that undergoes a gradual transition to replacement fertility. I model the fertility transition by specifying a linear frontier on the Lexis surface across which a change in fertility is instantaneous. Gradual transitions result from variations in the slope of this frontier. This framework can be used to reproduce and understand previous studies of population momentum and gradual transitions.     

Population registers and population statistics

The authors examine the use of population registers in the production of demographic statistics. "To do this, we first describe these registers; we then examine their further development as an independent source of population statistics--including current population estimates, vital and migration statistics--and as an alternative to population censuses. In conclusion, we consider a number of essential features of registers, including the original collection of data, the system's lifetime, privacy protection, and the government's ability to bring about a balance among conflicting interests regarding the collection and use of the data." The discussion is illustrated using examples from the Netherlands and Denmark.     

人口流动对农村人口老龄化的影响研究——基于“五普”和“六普”数据分析

我国农村人口老龄化程度和提高的速度全面超越了城市,这与当前的人口城市化进程密切相关。人口流动的年龄选择性,使得农村流出人口平均年龄和老年人口比例都远低于农村人口整体水平。流动人口内部在不断地"更新",年轻的流动人口不断替代年老的流动人口,从而保持较年轻的年龄结构,这种人口流动的年龄选择性加速了农村人口老龄化。通过人口老龄化模型的进一步分析发现,在2000～2010年间,农村人口自然老化速度基本保持稳定。而随着农村流动人口的增加,其对农村人口老龄化速度的影响从2000～2005年间的0.031岁/年增加到2006～2010年间的0.07岁/年;农村流出人口对农村人口平均年龄增加的贡献也从8.04%上升到16.91%,人口流动已成为农村人口老龄化的重要推动力。从人口流动的角度,需要关注农村留守老人的照料问题,进一步完善农村社会保障体系以及解决如何让流动人口在城市沉淀下来等问题。     

Population aging, health care, and growth

This paper constructs a small open two-sector (health care and non-health care) overlapping generations model and investigates how changes in the demand for health care induced by population aging influence the economy’s employment structure and per capita income growth rate. We show that population aging induces a shift in labor from the non-health care sector to the health care sector and lowers the per capita income growth rate. This paper also investigates public policy for child care and demonstrates the existence of an intergenerational conflict between current and future generations concerning public policy on child care.     

Some macroeconomic aspects of global population aging

Across the demographic transition, declining mortality followed by declining fertility produces decades of rising support ratios as child dependency falls. These improving support ratios raise per capita consumption, other things equal, but eventually deteriorate as the population ages. Population aging and the forces leading to it can produce not only frightening declines in support ratios but also very substantial increases in productivity and per capita income by raising investment in physical and human capital. Longer life, lower fertility, and population aging all raise the demand for wealth needed to provide for old-age consumption. This leads to increased capital per worker even as aggregate saving rates fall. However, capital per worker may not rise if the increased demand for wealth is satisfied by increased familial or public pension transfers to the elderly. Thus, institutions and policies matter for the consequences of population aging. The accumulation of human capital also varies across the transition. Lower fertility and mortality are associated with higher human capital investment per child, also raising labor productivity. Together, the positive changes due to human and physical capital accumulation will likely outweigh the problems of declining support ratios. We draw on estimates and analyses from the National Transfer Accounts project to illustrate and quantify these points.     

Demographic transition and population aging in Korea

"This paper describes the process of population aging in conjunction with the demographic transition in [South Korea]. Korea has recently experienced rapid decreases of both mortality and fertility, which have brought about the rapid process of population aging. The speed of...population aging in Korea is projected as one of the fastest in the world. Population aging brings about changing patterns of family composition, especially new trends of living arrangements of the elderly. Since the process of population aging [began] in Korea, the proportion of [those] living alone and [of those] living with spouse only have significantly increased."     

The momentum of population growth with time dependent net maternity function

The momentum of population growth problem of Keyfitz is generalized to contain a gradual change of the age-specific birth rate ro the level of bare replacement. Assuming a time dependence for the net maternity function of the form (formula: see text) R being the net reproductive rate, we show that for the Malthusian model the asymptotic birth rate is increased by exp (r/lambda), where r is the rate of increase of the population before t = 0. A numerical method for obtaining the asymptotic birth rate for a general net maternity function with the same time dependence is outlined.     

Population aging and PAYG pensions in the OLG model

This paper shows the effects on a pay-as-you-go pension system of the demographic change in the standard overlapping generations model. Firstly, we consider a setting with exogenous fertility and then a model with endogenous fertility. In both cases, population aging due to increased longevity implies a reduction in pensions payouts.     

Population trends and population policy in Ceylon

The population of Ceylon has many. features in common with other Asian countries. Ceylon has, however, the distinction of an unusual wealth of demographic data. The study of many problems of general interest to Asia may thus be made for Ceylon, and the conclusions in part extended to other Asian countries.     

Population, population density and technological change

In a model on population and endogenous technological change, Kremer (1993) combines a short-run Malthusian scenario where income determines the population that can be sustained, with the Boserupian insight that greater population spurs technological change and can therefore lift a country out of its Malthusian trap. We show that a more realistic version of the model, which combines population and population density, allows deeper insights into these processes. The incorporation of population density also allows a superior interpretation of the empirical regularities between the level of population, population density, population growth, and economic development at aggregated and disaggregated levels.