Cycles in the two-sex problem: an investigation of a nonlinear demographic model

"A fundamental shortcoming of classic stable population theory is its failure to handle populations differentiated by sex. The classic theory is linear while the two-sex problem is inherently nonlinear. Previous two-sex investigations have focused on equilibrium conditions rather than dynamics, and ignored competition between age groups for marriage partners. This study makes a start at analyzing dynamics and models that incorporate competition, which can play an important role in any realistic marriage model and can turn a model with a stable equilibrium sex ratio into one with a cycling equilibrium." This is a revised version of a paper originally presented at the 1990 Annual Meeting of the Population Association of America. (SUMMARY IN FRE)     

Heterogeneous sexual mixing in populations with arbitrarily connected multiple groups

"A simple procedure for constructing [social/sexual] mixing models for arbitrarily classified (e.g. by sex, age, geographical location, sexual preference) populations is outlined, including a scheme for finding the number of independent mixing parameters required, and a simple (linear algebra) means for finding the values of the dependent mixing parameters. Various worked examples are presented, including the two-sex problem and structured and selective mixing." The use of the models for analyzing mixing structures for AIDS transmission is assessed. (SUMMARY IN FRE)     

[An analysis of the sex ratios at birth of China].]

The sex ratio at birth in China is analyzed using data from the 1982 census. The focus is on geographic differentials in sex distribution and the impact of population density on those differentials. Findings indicate that the sex ratio at birth was lower in urban populations than in rural populations.     

Inheritance of sex ratio in the Kanzawa spider mite,Tetranychus kanzawai Kishida

Summary The frequency distributions in sex ratios of offspring from 4 fieldTetranychus kanzawai populations were examined. No significant difference was observed between average sex ratios of the 4 populations, although there was a great variability within each population, especially in the population fromPueraia lobata. Using the population fromP. lobata, inbred lines with high (H) and low (L) sex ratios were selected. Crossing experiments between H and L showed that sex ratio is determined by the genotype of mothers. It seemed that sex ratio is cointrolled by several genes, with no cytoplasmic factor involved.     

HIV Risk Among Men Who Have Sex with Men Only (MSMO) and Men Who Have Sex with Men and Women (MSMW) in Baltimore

Men who have sex with men and women (MSMW) are at high risk for HIV. However, the majority of research on populations of men who have sex with men (MSM) combines MSMW and men who have sex with men only (MSMO) samples, which limits our understanding of HIV risk behaviors and factors associated with HIV risk among MSMW populations. We used the BESURE-MSM2, a venue-based cross-sectional study of HIV risk behaviors among MSM in Baltimore, MD, to examine HIV risk among MSMW. MSMW were less likely to report unprotected receptive anal intercourse than MSMO (6.8% vs. 19.6%, p = .0024). Among MSMW, 43.0% reported unprotected sex with a woman in the past year, but only 19.4% reported unprotected sex with both men and women, representing only 5.0% of the total MSM sample. In multivariate analyses, we found that among MSMW having unprotected sex with women in the past year, disclosing same sex behavior and having a main female partner were associated with unprotected anal intercourse with male partners. HIV prevention programs for MSMW are needed that address the complex partnerships of MSMW and the social contextual factors within which relationships and behaviors are embedded.     

计划生育政策与出生性别比关系的重新解读——社会性别的视角

关于计划生育政策对出生性别比偏高的影响一直是理论界争论的一个热点。本文力图从社会性别的视角出发,在对计划生育政策的梳理、分析了计划生育政策的地区差异与出生性别比之间的关系的基础上,对二者之间的关系进行了重新的解读。     

The Implementation of Preferences for Male Offspring

Over the past quarter century the sex ratio at birth (SRB) has risen above natural levels in a number of countries, mostly in Asia. This rise has been made possible in populations with strong son preference by the increasing availability of safe, effective, and inexpensive technologies to determine the sex of a fetus and to end unwanted pregnancies. This article documents levels and trends in the sex ratio at birth, in preferences for male offspring (using information on desired number of girls and boys), and in the implementation of these preferences. DHS surveys from 61 countries in Africa, Asia, and Latin America and for Indian states are the main source of data. A comparison of desired with actual SRBs finds large gaps in most populations, implying a substantial pent‐up demand for male offspring and the technology to implement this preference. Two types of actions to implement preferences are considered: the practice of contraception to stop childbearing after the desired number of sons has been born and the use of sex‐selective abortion to avoid female births. The second part of the article discusses factors that could influence the SRB, including the promotion of gender equality, and the implications of these factors for future trends.     

Sex selection with biased technologies and its effect on the population sex ratio

Current biomedical research on sex selection techniques may soon offer couples the opportunity to choose the sex of their children with greater certainty. A technique planned for marketing by mid-1978 can increase the probability of bearing a son to as much as 0.90. However, couples who wish to improve their chances of bearing a daughter have no such opportunity. The purpose of this paper is two-fold. First, a decision-making model is provided which describes how couples should choose among alternative sex-selection methods so as to maximize the probability of bearing their desired number of sons and daughters. Second, the effect of the widespread use of sex-selection techniques on the population sex ratio is explored. It is shown that even if populations have unbiased sex preferences, or sex preferences biased towards daughters, the use of biased sex-selection technologies may result in very high population sex ratios.     

The Sources and Diversity of Immigrant Population Change in Australia, 1981–2011

Australia has one of the largest percentages of immigrant populations in the developed world with a highly regulated system of immigration control and regular censuses to track their changes over time. However, the ability to explain the population change through the demographic components of immigration, emigration, and death by age and sex is complicated because of differences in measurement and sources of information. In this article, we explore three methods for reconciling the demographic accounts from 1981 to 2011 for the Australia-born and 18 foreign-born population groups. We then describe how the immigrant populations have changed and what has contributed most to that change. We find that the sources of immigrant population change have varied considerably by age, sex, country of birth, and period of immigration. Immigrants from Europe are currently the oldest and slowest-growing populations, whereas those from elsewhere are growing rapidly and exhibit relatively young population age structures. Studying these patterns over time helps us to understand the nature of international migration and its long-term contributions to population change and composition.     

Environment and sex ratios among Alaska Natives: An historical perspective

Human-environment interactions can affect the sex ratios of resource-dependent societies in a variety of ways. Historical and contemporary data on Alaska Native populations illustrate such effects. Some eighteenth and early nineteenth century observers noted an excess of females, which they attributed to high mortality among hunters. Population counts in the later nineteenth century and well into the twentieth found instead an excess of men in many communities. Female infanticide was credited as the explanation: since family survival depended upon hunting success, males were more valued. Although infanticide explanations for the excess of males have been widely believed, available demographic data point to something else: higher adult female mortality. Finally, in the postwar years, the importance of mortality differentials seems to have faded- and also changed direction. Female outmigration from villages accounts for much of the gender imbalance among Native populations today. Natural-resource development, particularly North Slope oil, indirectly drives this migration. In Alaska's transcultural communities, the present gender imbalances raise issues of individual and cultural survival.     

On the Far Eastern pattern of mortality

Since the early 1980s, it has been accepted widely that there is a Far Eastern pattern of mortality, a pattern characterized by excessively high death rates among older men relative to death rates among younger men and among women. It has been regarded as a unique regional mortality pattern, applying primarily to Far Eastern populations. A re-examination of the mortality data of some Far Eastern populations reveals that changes in both age patterns of and sex differentials in mortality have been widely observed. Further, mortality patterns similar to the so-called Far Eastern mortality model have been found in many other populations.     

Estimating Mortality Level for Small Populations: An Evaluation of a Pair of Two-Census Methods

A pair of two-census methods of estimating mortality levels are tested with simulated census data. The populations considered range in size from 250 to 1500 individuals of each sex; censuses were taken at intervals of five and ten years. In general, the methods are resistant to bias, and yield variances similar in magnitude to those obtained using vital registration data and life table techniques for censored data. The two-census methods represent a substantial improvement over the techniques of mortality estimation previously available for small populations, since two reliable censuses are more likely to be available for these populations than complete vital registration.     

On the Far Eastern pattern of mortality

Since the early 1980s, it has been accepted widely that there is a Far Eastern pattern of mortality, a pattern characterized by excessively high death rates among older men relative to death rates among younger men and among women. It has been regarded as a unique regional mortality pattern, applying primarily to Far Eastern populations. A re-examination of the mortality data of some Far Eastern populations reveals that changes in both age patterns of and sex differentials in mortality have been widely observed. Further, mortality patterns similar to the so-called Far Eastern mortality model have been found in many other populations.     

Immigrant mothers’ preferences for children’s sexes: A register-based study of fertility behaviour in Norway

Parental sex preferences have been documented in many native populations, but much less evidence is available on immigrants’ preferences for the sexes of their children. Using high-quality longitudinal register data from Norway, a country with a recent immigration history, we estimate hazards regression models of third birth risks by the sex composition of the first two children. A central question in the extant literature is whether the sex preferences of immigrant mothers match those observed in their country of origin, or if cultural adaption to local conditions is more important. Our analyses indicate that the sex preferences of immigrants generally match those previously documented for their native population, especially in the case of son preferences. The pattern of sex preferences is unmodified by the mother’s exposure to the host society. In sum, our evidence generally supports theories emphasizing cultural persistence in preferences, rather than theories of adaption or immigrant selectivity.     

Preliminary evidence regarding the hypothesis that the sex ratio at sexual maturity may affect longevity in men

In human populations, variation in mate availability has been linked to various biological and social outcomes, but the possible effect of mate availability on health or survival has not been studied. Unbalanced sex ratios are a concern in many parts of the world, and their implications for the health and survival of the constituent individuals warrant careful investigation. We indexed mate availability with contextual sex ratios and investigated the hypothesis that the sex ratio at sexual maturity might be associated with long-term survival for men. Using two unique data sets of 7,683,462 and 4,183 men who were followed for more than 50 years, we found that men who reached their sexual maturity in an environment with higher sex ratios (i. e., higher proportions ofreproductively ready men) appeared to suffer higher long-term mortality risks than those in an environment with lower sex ratios. Mate availability at sexual maturity may be linked via several biological and social mechanisms to long-term survival in men.     

Sex preference for children in German villages during the fertility transition

In the past, parents' sex preferences for their children have proved difficult to verify. This study used John Knodel's German village genealogies of couples married between 1815 and 1899 to investigate sex preferences for children during the fertility transition. Event history analyses of couples' propensity to progress to a fifth parity was used to test whether the probability of having additional children was influenced by the sex composition of surviving children. It appears that son preference influenced reproductive behaviour: couples having only girls experienced significantly higher transition rates than those having only boys or a mixed sibset. However, couples who married after about 1870 began to exhibit fertility behaviour consistent with the choice to have at least one surviving boy and girl. This result represents a surprisingly early move towards the symmetrical sex preference typical of modern European populations.     

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.     

New insights into the Far Eastern pattern of mortality

Some of the highest levels of excess mortality of males found anywhere in the world were present in several Far Eastern populations during the 1960s and 1970s but have progressively disappeared since that time. This study uses cause-of-death data to determine the diseases responsible for the existence and attenuation of these sex differences in Hong Kong, Singapore, and Taiwan. The results indicate that respiratory tuberculosis is the single most important underlying cause of the existence and attenuation of the pattern, that the role of liver diseases is not clear cut, and that other causes (such as cardiovascular diseases) are also important. A review of numerous risk factors yields no compelling reason why these populations experienced such large sex differences in mortality. However, it seems likely that public health and biomedical improvements (particularly those related to the reduction in mortality from tuberculosis) played a critical role in the attenuation of the Far Eastern mortality pattern.     

Simple mathematical models to describe the rate of mating in insect populations

Summary Simple models are constructed to describe the rate of mating in insect populations. The models are based on the assumption of random mate-searching in a closed habitat, including four parameters, i.e., population size, sex ratio, searching efficiency and male's capacity on mating frequency. The modes of effects of these parameters on the rate of mating are analyzed and some principles deduced are discussed in relation to the mating process in natural populations. This study was supported by science research fund from the Ministry of Education.     

Consistent correction of data for aboriginal populations

A consistent correction procedure is used to determine improved, consistent estimates by sex of census age distributions, intercensal births, intercensal deaths and net migration by age for the Aboriginal populations of the Northern Territory, South Australia and Western Australia during the period 1986–91. Undercount estimates and life tables show the Aboriginal populations to have lower coverage in statistical collections and much higher death risks than the total Australian population. Inter-regional net migration estimates show that component of change can no longer be ignored.