On the dynamics of populations with two age groups

By restricting the number of age groups to two and by introducing continued fractions, the dynamics of populations with deterministically changing vital rates are completely specified at all times. Explicit expressions for the sequence of the product of population projection matrices are given. From these, relative age distribution and reproductive values to any desired accuracy are obtained as functions of the vital rates. Thus, the results given in this paper are stronger than any existing weak ergodic theorems.     

The role of medium conditioning in the population dynamics of the housefly

Summary The role of larval medium conditioning on the behavior of larvae and of ovipositing adults of the housefly,Musca domestica L., was investigated through behavioral preference tests. Larvae were strongly attracted to medium conditioned by themselves or other larvae, while adult females overwhelmingly oviposited in fresh medium. Medium conditioning occurs within a few hours after hatching of an egg cohort and is effective in preventing overcrowding of a single site by shutting off further oviposition within 24 hours after eggs are initially deposited. A model of medium conditioning optimizes density for developing larvae and could also provide for regulation of local larval populations. This study was carried out during the tenure of grants from the National Science Foundation (GB-35473) and The National Institutes of Health (1-R01-AI-10988-01) to the senior author.     

The narrowing sex differential in life expectancy in high-income populations: effects of differences in the age pattern of mortality

Using data from the Human Mortality Database for 29 high-income national populations (1751-2004), we review trends in the sex differential in e(0). The widening of this gap during most of the 1900s was due largely to a slower mortality decline for males than females, which previous studies attributed to behavioural factors (e.g., smoking). More recently, the gap began to narrow in most countries, and researchers tried to explain this reversal with the same factors. However, our decomposition analysis reveals that, for the majority of countries, the recent narrowing is due primarily to sex differences in the age pattern of mortality rather than declining sex ratios in mortality: the same rate of mortality decline produces smaller gains in e(0) for women than for men because women's deaths are less dispersed across age (i.e., survivorship is more rectangular).     

The narrowing sex differential in life expectancy in high-income populations: Effects of differences in the age pattern of mortality

Using data from the Human Mortality Database for 29 high-income national populations (1751–2004), we review trends in the sex differential in e(0). The widening of this gap during most of the 1900s was due largely to a slower mortality decline for males than females, which previous studies attributed to behavioural factors (e.g., smoking). More recently, the gap began to narrow in most countries, and researchers tried to explain this reversal with the same factors. However, our decomposition analysis reveals that, for the majority of countries, the recent narrowing is due primarily to sex differences in the age pattern of mortality rather than declining sex ratios in mortality: the same rate of mortality decline produces smaller gains in e(0) for women than for men because women's deaths are less dispersed across age (i.e., survivorship is more rectangular).     

重新认识恩格斯晚年的两种生产决定论——对两种生产理论的彻底反思

近几年理论界在尝试反思我国控制人口的基本理论———两种生产理论 ,但不彻底。笔者从“源头”上对恩格斯晚年的两种生产决定论作出重新认识 ,认为两种生产决定论明白无误 ,与“生产力是社会发展的最终决定力量”具有牵连性、依附性 ,前者是实践作用论 ,后者是实践的机制作用论 ,都是正确的。为此 ,应运用最新认识对过去的认识进行清理或梳理以建立新的人口理论     

Natural mortality at different population densities of a pine shoot moth,Evetria cristata

Summary A field population ofEvetria cristata was studied in 10 plots in 1962 and in 6 plots in 1963. These plots were divided into 2 or 3 groups of different population levels of the shoot moth in respective years. The survival of the insect was then analysed in these different groups of plots. The survival rate ofE. cristata from eggs to adults in the first generation was found always higher in the group with low population density, which indicates the existence of some factors that affect the population more severely when the insect is more abundant.Lissonota evetriae andPediobius sp. seemed to have killed more proportion of the hosts where the shoot moth density was high. However, the total effect of the all natural enemies was not always great in the plots with high density of the moth. The survival of the second generation of the moth in 1963 was observed to be much higher at any population level than in the other generations.     

Gender differences in life expectancy free of impairment at older ages

This article uses data from the United Kingdom Medical Research Council Cognitive Function and Ageing study (MRC CFAS) to analyze morbidity associated with three areas of impairment. We use cognitive status, functional status, and physical illness to examine differences in the proportion of time that older women and men will spend with co-morbidity. We also analyze differences among various impairments, and investigate the relationship between missing data and sex. Women have a larger burden of impairment than men, and, by including cognitive impairment together with functional impairment, a very large impairment burden is highlighted at all ages. Policy implications of the findings from the perspective of older women in the United Kingdom are discussed.     

Rectangularization revisited: Variability of age at death within human populations*

Rectangularization of human survival curves is associated with decreasing variability in the distribution of ages at death. This variability, as measured by the interquartile range of life table ages at death, has decreased from about 65 years to 15 years since 1751 in Sweden. Most of this decline occurred between the 1870s and the 1950s. Since then, variability in age at death has been nearly constant in Sweden, Japan, and the United States, defying predictions of a continuing rectangularization. The United States is characterized by a relatively high degree of variability, compared with both Sweden and Japan. We suggest that the historical compression of mortality may have had significant psychological and behavioral impacts.     

Moving from a decennial census to a continuous measurement survey: factors affecting nonresponse at the neighborhood level

The Census Bureau is testing a continuous measurement program, known as the American Community Survey (ACS), which will provide census “long form” data annually, though with slightly higher levels of sampling variability. This paper focuses on the 1999–2001 ACS in the Bronx, 1 of 31 ACS test sites. It examines whether the quality of ACS data in the Bronx varies across neighborhoods, focusing specifically on how neighborhood sociodemographic factors influence nonresponse, as measured by mail return and allocation rates. It also examines whether these neighborhood factors have a differential impact on nonresponse in the ACS and the 2000 decennial census, and discusses reasons why this may be so.The ACS mail return rates are not only lower than those of the census, but are highly sensitive to race and socioeconomic distress. Despite this initial disadvantage, the ACS has lower levels of allocation on key variables, relative to the 2000 Census. Moreover, the effect of neighborhood socioeconomic distress on allocation rates in the ACS was minimal, compared to its effect on census allocation. We find that the overall quality of ACS data in the Bronx is superior to that of the decennial census. Our analysis of Bronx data suggests that the proposed elimination of the decennial long form and its replacement with the ACS is a reasonable tradeoff for users of small area data.     

Conditions determining the local stability of populations

The conditions that determine the local stability classification of an equilibrium population configuration are analyzed. The population investigated is age-structured and density-dependent, where density is determined by an age-weighted population size. 2 demographic parameters are introduced: the marginal birth rate and the marginal death rate, which describe the marginal density-dependence of the birth and death rates of the equilibrium population. Certain necessary and/or sufficient conditions determining stability are developed, most of them involving the net reproduction rate of the population, and examples illustrating these conditions are presented.     

Conditions determining the local stability of populations

The conditions that determine the local stability classification of an equilibrium population configuration are analyzed. The population investigated is age‐structured and density‐dependent, where density is determined by an age‐weighted population size. Two demographic parameters are introduced: the marginal birth rate and marginal death rate, which describe the marginal density‐dependence of the birth and death rates of the equilibrium population. Certain necessary and/or sufficient conditions determining stability are developed, most of them involving the net reproduction rate of the population, and examples illustrating these conditions are presented.     

Searching the databases: a quick look at Amazon and two other online catalogues

The Amazon Online Catalogue was compared with the Library of Congress Catalogue and the British Library Catalogue, both also available online, by searching on both neutral (Gay, Lesbian, Homosexual) and pejorative (Perversion, Sex Crime) subject terms, and also by searches using Boolean logic in an attempt to identify Lesbian Fiction items and religion-based anti-gay material. Amazon was much more likely to be the first port of call for non-academic enquiries. Although excluding much material necessary for academic research, it carried more information about the individual books and less historical homophobic baggage in its terminology than the great national catalogues. Its back catalogue of second-hand books outnumbered those in print. Current attitudes may partially be gauged by the relative numbers of titles published under each heading--e.g., there may be an inverse relationship between concern about child sex abuse and homophobia, more noticeable in U.S. because of the activities of the religious right.     

Race differences in age at first birth and the pace of subsequent fertility: Implications for the minority group status hypothesis

We examine race differences in the effects of age at first birth on the pace of subsequent fertility. If race differences in the pace of fertility persist net of age at first birth and socioeconomic variables, they will be taken as new support for the minority group status hypothesis. Data from the 1973 National Survey of Family Growth are analyzed with the finding that race differences in the pace of fertility are real, giving support to the hypothesis. Implications are drawn suggesting that the proper points at which to examine group differences in fertility are the different stages in the process which culminates in completed fertility, rather than limiting investigation to the final product.     

The data and the dynamics of the Chinese populations

Historical demographic data on populations of the Chinese cultural area including counts, registrations, and continuous records are discussed in terms of problems of analysis. For many decades, censuses, investigations, and registration reports yielded generally faulty data on the numbers, and the age and sex structures of the populations. The problem here is not the adjustment of age and sex structures, but the use of faulty structures to estimate the dynamics of the population in the absence of either successive investigations or vital statistics. This paper analyzes these problems according to historical eras (Chinese Farm Population 1919-1932) or geographical areas (Taiwan, Manchuria, etc.). The writer concludes that further pursuit of estimates that agree with the Chinese demographic realities of the period requires a) a wider integration of comparable data and b) adjustment of age structures in relation to the habitual errors in response, the systematic biases in registration, and the deviations reflecting erratic factors or historic events.     

Comparison of male adult population densities of the oriental and artocarpus fruit flies,Dacus spp. (Diptera: Tephritidae), in two nearby villages in Penang, Malaysia

Summary The populations of native male adult oriental fruit flyDacus dorsalis (Hendel) and artocarpus fruit flyD. umbrosus (F.) in two selected site (BU and SD) were estimated weekly by the capture-recapture technique using live traps baited with methyl eugenol. In BU where many varieties of fruit trees were grown, the estimated population densities ofD. dorsalis were between 980 and 3100 male flies per ha between May and July, 1984. During the same period, in SD where there were fewer number and varieties of fruit trees, the estimated population densities were between 300 and 1000 flies per ha. The estimated population densities ofD. umbrosus over the same period were between 570 and 1290 flies per ha in BU; and between 5 and 95 flies per ha in SD. Of a total 6828 markedD. dorsalis flies released only one fly (released 6 weeks earlier in BU) was caught in a different site.