Assessing Validity and Application Scope of the Intrinsic Estimator Approach to the Age-Period-Cohort Problem

In many different fields, social scientists desire to understand temporal variation associated with age, time period, and cohort membership. Among methods proposed to address the identification problem in age-period-cohort analysis, the intrinsic estimator (IE) is reputed to impose few assumptions and to yield good estimates of the independent effects of age, period, and cohort groups. This article assesses the validity and application scope of IE theoretically and illustrates its properties with simulations. It shows that IE implicitly assumes a constraint on the linear age, period, and cohort effects. This constraint not only depends on the number of age, period, and cohort categories but also has nontrivial implications for estimation. Because this assumption is extremely difficult, if not impossible, to verify in empirical research, IE cannot and should not be used to estimate age, period, and cohort effects.     

An Assessment and Extension of the Mechanism-Based Approach to the Identification of Age-Period-Cohort Models

Many methods have been proposed to solve the age-period-cohort (APC) linear identification problem, but most are not theoretically informed and may lead to biased estimators of APC effects. One exception is the mechanism-based approach recently proposed and based on Pearl’s front-door criterion; this approach ensures consistent APC effect estimators in the presence of a complete set of intermediate variables between one of age, period, cohort, and the outcome of interest, as long as the assumed parametric models for all the relevant causal pathways are correct. Through a simulation study mimicking APC data on cardiovascular mortality, we demonstrate possible pitfalls that users of the mechanism-based approach may encounter under realistic conditions: namely, when (1) the set of available intermediate variables is incomplete, (2) intermediate variables are affected by two or more of the APC variables (while this feature is not acknowledged in the analysis), and (3) unaccounted confounding is present between intermediate variables and the outcome. Furthermore, we show how the mechanism-based approach can be extended beyond the originally proposed linear and probit regression models to incorporate all generalized linear models, as well as nonlinearities in the predictors, using Monte Carlo simulation. Based on the observed biases resulting from departures from underlying assumptions, we formulate guidelines for the application of the mechanism-based approach (extended or not).     

The Elderly and the Extended Household in Portugal: An Age-Period-Cohort Analysis

Portugal, a southern European country, is expected to exhibit a relatively large proportion of extended households. However, following some general trends associated with large social transformations, Portugal is also expected to have an increasingly larger proportion of nuclear families. We use data from the eight waves of ECHP (European Community Household Panel), covering the years from 1994 to 2001, to establish whether these expectations are justified. Among the nuclear households that include elderly members, we isolate those corresponding to single-person households, since they are particularly relevant for policy purposes. Separate analyses are carried out for the elderly with health problems and for those with no health problems, in order to detect different patterns of living arrangements. We also project the living arrangements until 2005, based on an age-period-cohort analysis. We find that the extended households are a very significant form of living arrangement with reference to the Portuguese elderly, and a living arrangement whose importance is not declining over time. In particular, the oldest old constitutes the group that tends to be found living most frequently in extended households, while those with health problems start much earlier than those with no health problems to live in extended households as they grow older. The proportion of individuals aged 65+ living alone has somewhat decreased, but the proportion of this type of household largely increases with age.

Migration and Pacific Mortality: Estimating Migration Effects on Pacific Mortality Rates Using Bayesian Models

Pacific people living in New Zealand have higher mortality rates than New Zealand residents of European/Other ethnicity. The aim of this paper is to see whether Pacific mortality rates vary by natality and duration of residence. We used linked census-mortality information for 25- to 74-year-olds in the 2001 census followed for up to three years. Hierarchical Bayesian modeling provided a means of handling sparse data. Posterior mortality rates were directly age-standardized. We found little evidence of mortality differences between the overseas-born and the New Zealand–born for all-cause, cancer, and cardiovascular disease (CVD) mortality. However, we found evidence for lower all-cause (and possibly cancer and CVD) mortality rates for Pacific migrants resident in New Zealand for less than 25 years relative to those resident for more than 25 years. This result may arise from a combination of processes operating over time, including health selection effects from variations in New Zealand’s immigration policy, the location of Pacific migrants within the social, political, and cultural environment of the host community, and health impacts of the host culture. We could not determine the relative importance of these processes, but identifying the (modifiable) drivers of the inferred long-term decline in health of the overseas-born Pacific population relative to more-recent Pacific migrants is important to Pacific communities and from a national health and policy perspective.     

结构方程模型在妇女生育行为研究中的应用:以深圳市为例

本文利用“深圳市龙岗区流动人口计划生育管理与服务状况”调查数据 ,运用结构方程模型 (SEM)对深圳流动育龄妇女的生育行为进行了尝试性的分析 ,克服了传统统计方法无法处理自变量测量误差的局限性。研究结果表明 ,对生育行为最大的影响因素是生育意愿。经济因素对生育行为的影响是双向的 ,一方面经济水平的提高可以产生孩子质量 -数量替代效应 ;另一方面在生育意愿没有改变前 ,经济水平提高对生育行为也会有促进作用。最后 ,提出了结构方程模型在生育行为研究和计划生育实践的应用前景     

Strategic HR Management with an Aging Workforce: Using Demographic Models to Determine Optimal Employment Policies

A key component of the strategic plan for any company is the determination of the optimal number of workers needed to produce the desired level of output. Unless workers of different ages have the same skills and productivity, managers must also decide on the best age structure of their workforce and adopt compensation and employment policies to achieve these objectives. Employer responses to the shifts in the demand for their output impact the age distribution of the workforce while employment and compensation policies influence age specific hiring, retention, and retirement rates. This paper examines how demographic models can be used to project the future age structure of a labor force. In addition, we describe how compensation policies can be used to alter trends in the age distribution of employees. Thus, employers can develop strategic plans for achieving the desired labor force.     

Using Discrete-Time Event History Fertility Models to Simulate Total Fertility Rates and Other Fertility Measures

Event history models, also known as hazard models, are commonly used in analyses of fertility. One drawback of event history models is that the conditional probabilities (hazards) estimated by event history models do not readily translate into summary measures, particularly for models of repeatable events, like childbirth. In this paper, we describe how to translate the results of discrete-time event history models of all births into well-known summary fertility measures: simulated age- and parity-specific fertility rates, parity progression ratios, and the total fertility rate. The method incorporates all birth intervals, but permits the hazard functions to vary across parities. It can also simulate values for groups defined by both fixed and time-varying covariates, such as marital or employment life histories. We demonstrate the method using an example from the National Survey of Family Growth and provide an accompanying data file and Stata program.     

Probabilistic Forecasting Using Stochastic Diffusion Models, With Applications to Cohort Processes of Marriage and Fertility

In this article, we show how stochastic diffusion models can be used to forecast demographic cohort processes using the Hernes, Gompertz, and logistic models. Such models have been used deterministically in the past, but both behavioral theory and forecast utility are improved by introducing randomness and uncertainty into the standard differential equations governing population processes. Our approach is to add time-series stochasticity to linearized versions of each process. We derive both Monte Carlo and analytic methods for estimating forecast uncertainty. We apply our methods to several examples of marriage and fertility, extending them to simultaneous forecasting of multiple cohorts and to processes restricted by factors such as declining fecundity.     

Models and Proposals for Malaria: A Review

Mathematical models to study the dynamics of malaria continue to be developed and upgraded on the parasite component, which is the causative agent for malaria; on the human component that serves as a reservoir of infection for the blood feeding female mosquitoes; on the disease transmitting vector, the component mostly responsible for the movement of the parasite agent from one human to another; or on the life cycle of the malaria parasite as a pathogen both within the human and vector populations. The consideration of so-far neglected features can be beneficial for the control of malaria.     

Intrinsic Growth Rates and Net Reproduction Rates in the Presence of Migration

Conventional measures of long‐term population growth such as the intrinsic growth rate and the net reproduction rate assume migration rates to be zero. We develop expressions for analogous measures that register the impact of net migration rates, and we develop a simple method of estimating their values. Applying these new measures to data for developed countries shows that allowance for migration raises net reproduction rates by 0.2‐0.3 in areas of overseas European settlement and by approximately half as much in Northern and Western Europe. The newly defined intrinsic growth rates in Eastern Europe are exceptionally low at ‐1.7 percent to ‐2.4 percent per annum. In contrast, the migration‐adjusted intrinsic growth rate of the United States exceeds those of Asia and Latin America. The formulas and estimation procedures described should allow a more precise understanding of the implications of current migration patterns for long‐term growth prospects.     

Marginal Utility and Economic Development: Intrinsic Versus Extrinsic Aspirations and Subjective Well-Being Among Chinese Employees

The post-1979 economic reforms have led to impressive economic growth in China both in terms of gross domestic product and individual income. Individual well-being, however, has not increased on par with the economy (Brockmann et al. in J Happiness Stud 10(4):387–405, 2009; Easterlin et al. in Proc Natl Acad Sci 109(25):9775–9780, 2012). In the current series of studies, traditional and multilevel regression models are applied to examine the relationship between income and employee well-being. Results suggest a curvilinear relationship between income and satisfaction (both with one’s job and one’s income), supporting a diminishing marginal utility effect. Additionally, confirming a central postulate of Goal Contents Theory (GCT), individuals who espoused the importance of income (an extrinsic motive) were less satisfied with income itself. Further examining the application of GCT in a Chinese context, results suggest individuals who value extrinsic motives (i.e., money, possessions, fame) exhibit lower levels of job satisfaction, life satisfaction, and feelings of accomplishment. Finally, there is a significant multilevel effect such that between-city levels of health have a significant positive relationship with life satisfaction. These results offer organizational and policy implications related to the interaction between economic prosperity and human development.     

Fecundability and the Frequency of Marital Intercourse: A Critique of Nine Models

The biological and demographic literature on the effects or frequency of intercourse on fecundability is reviewed in this paper. While empirical work and model-building results agree well on the effect of change from low to moderate coital frequencies, inconsistencies emerge when increase from moderate to high coital frequencies is considered. Of the models considered, it may be argued that the explicit provision for unfavourable cycles makes Schwartz's model an improvement over Barrett and Marshall's, Lachenbruch's and Trussell's. Moreover, even though he used a very different approach, Bongaarts obtained results that are much closer to those of Schwartz et al. than the others. Bongaarts's model is used as a starting point for new modelling, to be reported in the next issue, which deals with these inconsistencies by taking into account the ageing of gametes.     

Fecundability and the Frequency of Marital Intercourse: New Models Incorporating the Ageing of Gametes

A companion paper in the last issue reviewed the literature on effects of frequency of intercourse on fecundability. At moderately high coital frequencies, predicted effects of further increases on fecundability based on previous work vary widely. New modelling reported here, designed to take into account the ageing of gametes, attempts to identify a set of limits within which the true relationship of coital frequency and fecundability at moderate to high frequencies may confidently be expected to lie.     

Long-range trends in adult mortality: Models and projection methods

In the study reported here, I had two objectives: (1) to test a new version of the logistic model for the pattern of change over time in age-specific adult mortality rates and (2) to develop a new method for projecting future trends in adult mortality. A test of the goodness of fit of the logistic model for the force of mortality indicated that its slope parameter is nearly constant over time. This finding suggests a variant of the model that is called the shifting logistic model. A new projection method, based on the shifting mortality model, is proposed and compared with the widely used Lee-Carter procedure.     

Health-Related Quality of Life Models: Systematic Review of the Literature

Purpose: This review evaluates howtheory-driven models of health-related qualityof life (QoL) take into account themethodological and conceptual problemsbesetting the field. Methodology: 68 modelsformulated from 1965 to 2001 (60% of thosefound for each decade) were randomly selected.Two judges evaluated the models using ananalysis grid covering a) the models' level ofconceptualization (from less to moresophisticated); b) the definition of QoL; c)the distinction between factors that mayinfluence QoL and QoL per se; and d) thepresence of instruments as tools to measureQoL. A global score reflecting the overallquality of the models was also provided.Results: Of the 68 theory-driven modelssampled, approximately 35% were in the lesscomplex category, 15% were in the mostsophisticated group and nearly 50% were inbetween. QoL was not defined by at least 25%of authors. The distinction between factorsthat may influence QoL and QoL per se wasmade in less than 50% of models. Instrumentsused were identified by 78% of authors. Lessthan 3% of the models examined received themaximum global score. Conclusions: From 1965 to2001, a general improvement in the quality ofQoL models is identified. However, for manymodels, the questions used to analyze modelswere not always clearly addressed (many did noteven define QoL), rendering analysis quitedifficult. Overall, the field needs moresophisticated models and a better definition ofthe content and boundaries of the QoL concept.     

Quantifying Intrinsic and Extrinsic Contributions to Human Longevity: Application of a Two-Process Vitality Model to the Human Mortality Database

The rise in human life expectancy has involved declines in intrinsic and extrinsic mortality processes associated, respectively, with senescence and environmental challenges. To better understand the factors driving this rise, we apply a two-process vitality model to data from the Human Mortality Database. Model parameters yield intrinsic and extrinsic cumulative survival curves from which we derive intrinsic and extrinsic expected life spans (ELS). Intrinsic ELS, a measure of longevity acted on by intrinsic, physiological factors, changed slowly over two centuries and then entered a second phase of increasing longevity ostensibly brought on by improvements in old-age death reduction technologies and cumulative health behaviors throughout life. The model partitions the majority of the increase in life expectancy before 1950 to increasing extrinsic ELS driven by reductions in environmental, event-based health challenges in both childhood and adulthood. In the post-1950 era, the extrinsic ELS of females appears to be converging to the intrinsic ELS, whereas the extrinsic ELS of males is approximately 20 years lower than the intrinsic ELS.     

Intrinsic and Extrinsic Goals: Their Structure and Relationship to Well-Being in German and U.S. College Students

Aspirations for intrinsic (e.g.,self-acceptance, affiliation, community feeling)versus extrinsic (e.g., financial success, appearance,social recognition) goals were examined in German andU.S. college students. The structure of studentsgoal-systems in terms of goal content was remarkablysimilar in the two cultures, as evidenced byexamination of the ordering of goals. Also, as inpast work in the U.S., German college students whowere especially focused on intrinsic goals had highwell-being, whereas the reverse was true for a focuson extrinsic goals. Some differences between thecultures in terms of specific goals are alsodiscussed.     

Models of midwifery care for Indigenous women and babies: A meta-synthesis

Issue

Indigenous women in many countries experience a lack of access to culturally appropriate midwifery services. A number of models of care have been established to provide services to women. Research has examined some services, but there has not been a synthesis of qualitative studies of the models of care to help guide practice development and innovations.