[A cross-section of a stable population as a point of departure for the study of models of demographic behavior: the case of Antwerp at the end of the eighteenth century].
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Belgium↗
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Results for “Demographic modelling”
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Towards a computerized demographic microsimulation model for Egypt: experimentation of POPSIM: 1.
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Africa↗
National development, transmigration models and demographic trends in Indonesia.
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Asia↗
Disease transmission models with density-dependent demographics.
The models considered for the spread of an infectious disease in a population are of SIRS or SIS type with a standard incidence expression. The varying population size is described by a modification of the logistic differential equation which includes a term for disease-related deaths. The models have density-dependent restricted growth due to a decreasing birth rate and an increasing death rate as the population size increases towards its carrying capacity. Thresholds, equilibria and stability are determined for the systems of ordinary differential equations for each model. The persistence of the infectious disease and disease-related deaths can lead to a new equilibrium population size below the carrying capacity and can even cause the population to become extinct.
Animals↗
Impact of demographic distribution and population growth rate on haplotypic diversity linked to a disease gene and their consequences for the estimation of recombination rate: example of a French Canadian population.
A disease gene introduced into a rapidly growing population by a single individual remains in strong linkage disequilibrium with the surrounding molecular markers. Mapping strategies taking advantage of this phenomenon allow increased mapping resolution as compared to pedigree analysis. Demographic models underlying these strategies usually assume the population exponential growth approximated by Poisson distribution of the number of children per individual. Knowing the real demographic distribution in the studied French-Canadian population, we analyzed the validity of the Poisson approximation. We adapted the existing model of the Poisson branching process to the case of a rapidly growing population and to non-Poisson distributions. In consequence, we were able to apply maximum-likelihood methods to estimate the recombination rate under various demographic scenarios. Our analysis shows that the growth rate has a higher impact on the estimation of recombination rate than the shape of the demographic distribution. The choice of the demographic model (Poisson vs. non-Poisson) has little effect on the estimation of the recombination rate but affects the expected distribution of haplotype frequencies. This distribution, however, depends much more on the population growth rate. Finally, we also demonstrate the usefulness of the Luria-Delbrück method, which gives a correct estimation of the recombination rate in a growing population, provided the sampling error is taken into account in the confidence intervals.
Confidence Intervals↗
A new class of dynamic macrosystem models with self-reproduction.
"The author considers a class of macrosystems where the relaxation time of the distribution process of elements is significantly less than the relaxation time of the self-reproduction process. The proposed model of such macrosystems defines the system of differential equations with nonlinearity generated by the solution of a mathematical programming problem with an entropy objective function. Methods for the structural analysis of this model are considered, and applications to demographic modelling, biological dynamics and chemical kinetics are given."
Demography↗
Alcoholism treatment demand estimation.
There is a critical need to accurately determine the alcoholism treatment needs in a particular area so that treatment resources can be effectively allocated. Currently, many state planning agencies determine resource allocation based solely upon the population's utilization of existing treatment facilities. This demand approach for determining treatment needs omits the population subgroups who have need for treatment but may not be utilizing existing facilities. The preferred method of alcohol treatment assessment is to focus on need determination vs. demand measurement. For purposes of this paper, need is defined as those in need of treatment form problems reacted to alcoholism, while demand for treatment includes those currently participating in a treatment program. In an effort to simplify the understanding of need assessment, a framework has been proposed for grouping and classifying the various alcoholism treatment assessment models. The initial phase of the model differentiates between demand vs. need assessment models. Next, need assessment models are grouped into four broad subgroups: (1) survey based models, (2) mortality based models, (3) treatment and mortality based models, and (4) multi-factor statistical based models. The final phase of the model presents a classification of demand based models. The demand based models include two types: (1) simple utilization models and (2) utilization combined with demographic models.
Alcoholism↗
Chaotic population dynamics can result from natural selection.
The question of whether animal populations display chaotic dynamics has motivated a thriving body of research for two decades. Yet unambiguous evidence for chaos in the wild remains scarce. Accordingly, it has been proposed that evolutionary forces act to preserve populations from chaos as well as oscillations. We have tested for this hypothesis by considering the dynamics associated with evolutionarily stable life histories (including age of maturity, adult survivorship and recruitment to adulthood) in a simple, but general, demographic model. Contrary to expectation, individual selection operating on demographic traits should often lead to oscillatory or chaotic dynamics for species with late feasible ages of maturity and many age classes. Also, the optimality of chaos is more likely whenever trade-offs constrain recruitment to rapidly decrease with increasing adult survival or decreasing age of maturity. Our results bring evolutionary support to the possibility that chaotic population dynamics might be much more widespread than inferred until now from data analyses. Furthermore, these findings provide novel support for the view that chaos could be an optimal regime for several biological systems.
Aging↗
Methods to estimate the number of orphans as a result of AIDS and other causes in Sub-Saharan Africa.
OBJECTIVE: To derive methods to estimate and project the fraction of children orphaned by AIDS and other causes. METHODS: HIV/AIDS affects orphan numbers through increased adult and child mortality and reduced fertility of HIV-positive women. We extend an epidemiologic and demographic model used previously to estimate maternal orphans to paternal orphans. We account for the impact of HIV/AIDS on child survival by modeling the HIV status of the partners of men who die of AIDS or other causes based on data on the concordance of heterosexual partners. Subsequently, the proportion of orphans whose parents have both died is predicted by a regression model fitted to orphanhood data from 34 national demographic and health surveys (DHSs). The approach is illustrated with an application to Tanzania and compared with DHS estimates for the years 1992 and 1999. RESULTS: Projections of the number and age distribution of orphans using these methods agree with survey data for Tanzania. They show the rise in orphanhood over the last decade that has resulted from the HIV epidemic. CONCLUSIONS: The methods allow estimation of the numbers of children whose mother, father, or both parents have died for countries with generalized heterosexual HIV epidemics. These methods have been used to produce orphan estimates for high-prevalence countries published by Joint United Nations Program on HIV/AIDS, World Health Organization, United Nations Children's Fund, and US Agency for International Development in 2002 and 2004.
Acquired Immunodeficiency Syndrome↗
A genealogical interpretation of linkage disequilibrium.
The degree of association between alleles at different loci, or linkage disequilibrium, is widely used to infer details of evolutionary processes. Here I explore how associations between alleles relate to properties of the underlying genealogy of sequences. Under the neutral, infinite-sites assumption I show that there is a direct correspondence between the covariance in coalescence times at different parts of the genome and the degree of linkage disequilibrium. These covariances can be calculated exactly under the standard neutral model and by Monte Carlo simulation under different demographic models. I show that the effects of population growth, population bottlenecks, and population structure on linkage disequilibrium can be described through their effects on the covariance in coalescence times.
Data Interpretation, Statistical↗
[Towards the inclusion of health state in the Israeli risk-adjustment scheme using medical diagnoses--some intermediate results].
BACKGROUND: A proper risk-adjustment mechanism in the allocation of funds to the health funds is a key element in the efficiency and equity of the health system. Since 1995, the Israeli risk-adjustment is based only on age, while, in many similar systems, considerable effort has been made to include health state as a risk-adjuster. OBJECTIVES: This study aims to suggest a risk-adjusted capitation scheme based on inpatient diagnoses. METHODS: Using the DxCG software and the MOH's hospitalization database for the period 1994-1997, the authors built a preliminary model to predict inpatient costs at a given year, based on diagnoses, age and sex in previous-year hospitalizations. The second stage, in which total health care costs are predicted based on the same previous-year information, has not been realized because of lack of cooperation from the health funds. RESULTS: The use of the DxCG diagnoses model with the Israeli data is feasible. However, further research is needed to construct the best Israeli model. The prediction of inpatient cost according to the diagnoses model is superior to that obtained by the demographic model.
Costs and Cost Analysis↗
The new Kuznets cycle: a test of the Easterlin-Wachter-Wachter hypothesis.
The aim of this paper is to evaluate the Easterlin-Wachter-Wachter model of the effect of the size of one generation on the size of the succeeding generation. An attempt is made "to identify and test empirically each component of the Easterlin-Wachter-Wachter model..., to show how the components collapse to give a closed demographic model of generation size, and to investigate the impacts of relative cohort size on the economic performance of a cohort." The models derived are then used to generate forecasts of the U.S. birth rate to the year 2050. The results provide support for the major components of the original model.
Americas↗
Genetic analysis of complex demographic scenarios: spatially expanding populations of the cane toad, Bufo marinus.
Inferring the spatial expansion dynamics of invading species from molecular data is notoriously difficult due to the complexity of the processes involved. For these demographic scenarios, genetic data obtained from highly variable markers may be profitably combined with specific sampling schemes and information from other sources using a Bayesian approach. The geographic range of the introduced toad Bufo marinus is still expanding in eastern and northern Australia, in each case from isolates established around 1960. A large amount of demographic and historical information is available on both expansion areas. In each area, samples were collected along a transect representing populations of different ages and genotyped at 10 microsatellite loci. Five demographic models of expansion, differing in the dispersal pattern for migrants and founders and in the number of founders, were considered. Because the demographic history is complex, we used an approximate Bayesian method, based on a rejection-regression algorithm, to formally test the relative likelihoods of the five models of expansion and to infer demographic parameters. A stepwise migration-foundation model with founder events was statistically better supported than other four models in both expansion areas. Posterior distributions supported different dynamics of expansion in the studied areas. Populations in the eastern expansion area have a lower stable effective population size and have been founded by a smaller number of individuals than those in the northern expansion area. Once demographically stabilized, populations exchange a substantial number of effective migrants per generation in both expansion areas, and such exchanges are larger in northern than in eastern Australia. The effective number of migrants appears to be considerably lower than that of founders in both expansion areas. We found our inferences to be relatively robust to various assumptions on marker, demographic, and historical features. The method presented here is the only robust, model-based method available so far, which allows inferring complex population dynamics over a short time scale. It also provides the basis for investigating the interplay between population dynamics, drift, and selection in invasive species.
Animals↗
Forecasting Australian marriage rates.
"The paper discusses the problem of modelling demographic variables for the purpose of forecasting. Two empirical model selection procedures are applied to suggest final form forecasting equations for Australian marriage rates. The suggested models are then assessed by comparing their post-sample forecast performance with that of univariate ARMA-type models of marriage rates which are regarded as approximations to marriage rate final equation models. In this instance the ARMA models are preferred for forecasting purposes. The properties of the ARMA model forecasts are then examined and the modelling strategy is contrasted with the regression method used by Withers."
Australia↗
[Calculating the intrinsic growth rate: comparison of definition and model].
It was shown that well known equation r = ln[N(t2)/N(t1)]/(t2 - t1) is the definition of the average value of intrinsic growth rate of population r within any given interval of time t2-t1 and changing arbitrarity its numbers N(t). The common opinion considering the equation as suitable only for exponentially growing population was found to be incorrect. The fundamentally different approach is based on the calculation of r within the framework of demographic model, realized as Euler - Lotka equation or population projection matrices. However this model requires simultaneous realization of several assumptions improbable for natural populations: exponential change in population size, stable age structure and maintaining constant age-dependent birth and death rates. The calculation of r by definition requires the data on the dynamics of population numbers, whereas calculation on the basis of the model requires the demographic tables of birth and death rate, but not the population numbers. With the example of American ginseng it was shown that evalution of r by definition and model approaches could produce opposite results.
Models, Theoretical↗
Theoretical population dynamics model of a genetically transmitted disease: sickle-cell anaemia.
We formulate a realistic demographic model that captures the pattern of inheritance of the S gene, which is responsible for the most common genetic defect, namely, sickle-cell anaemia (SCA), using general pair formations. The model equation is implicitly solved via the Laplace transform technique, while the existence of a unique solution is proved by applying the contraction mapping principle. One of the main results is the boundedness of the solution. A fundamental reason for the persistence of SCA is probably due to the role played by the selective advantage of the abnormal S gene over the normal haemoglobin A in tropical regions, and the fact that carriers are more fertile and survive longer (a property known as hybrid vigor), because they are essentially asymptomatic. We also discuss possible public health policies.
Anemia, Sickle Cell↗
Health-based risk adjustment Improving the pharmacy-based cost group model to reduce gaming possibilities.
The pharmacy-based cost group (PCG) model uses medication prescribed to individuals in a base-year as marker for chronic conditions which are employed to adjust capitation payments to their health plans in the subsequent year. Although the PCG model enhances predictive performance, possibilities for gaming may arise as it is based on prior utilization. This study investigates several strategies to mitigate this problem. The best strategies appear to be: use a (high) number of prescribed daily doses to assign persons to PCGs, do not allow for comorbidity, and remove PCGs with low future costs. This PCG model accounts for almost twice as much variance as do demographic models. In 2002 the Dutch government implemented this model in the sickness fund sector (two-thirds of the population).
Journal Article↗
Genome-wide insights into the evolutionary and demographic history of the red alga Mazzaella laminarioides: Evidence for speciation with ancient migration along the southeast Pacific coast.
The mechanisms driving lineage divergence in red algae remain unexplored, despite the group's remarkable diversity and ancient evolutionary history. The red alga Mazzaella laminarioides, a Chilean intertidal species complex composed of three parapatric cryptic lineages (North, Center, South), offers a valuable system to evaluate these processes, as its life history combines severe dispersal limitation with a haploid-diploid cycle that may influence the emergence of reproductive barriers. We reconstructed its evolutionary history using whole-genome sequencing and nuclear genome assembly of representative individuals from each lineage. Phylogenomic analyses based on 1,507 single-copy orthologs recovered three deeply divergent lineages with limited nuclear discordance consistent with incomplete lineage sorting. For both splits, demographic modelling was most consistent with an Ancient Migration scenario, although support over strict isolation was moderate, suggesting that divergence may have begun with low asymmetric ancestral gene flow followed by subsequent loss of connectivity, demographic bottlenecks, and later population expansion. Coding sequence analyses revealed lineage-specific dN/dS heterogeneity; only one South-lineage locus passed FDR correction (metaxin-1, mitochondrial protein import), with two further South-lineage candidates in chlorophyll and heme biosynthesis falling below the FDR threshold. Together, these signals suggest that divergent selective pressures on energy acquisition may have contributed to divergence at the southern end of the distribution. These results add to the small but growing body of whole-genome data for red algae and, alongside recent macroalgal studies, suggest that ancestral connectivity could be a recurrent feature of lineage divergence even in marine organisms with extremely restricted dispersal.
Rhodophyta↗