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PubMed1984

The analysis of linkages in demographic theory.

Many seemingly different questions that arise in the analysis of population change can be phrased as the same technical question: How, within a given demographic model, would variable y change if the age- or time-specific function f were to change arbitrarily in shape and intensity? At present demography lacks the machinery to answer this question in analytical and general form. This paper suggests a method based on modern functional calculus for deriving closed-form expressions for the sensitivity of demographic variables to changes in input functions or schedules. It uses this "linkage method" to obtain closed-form expressions for the response of the intrinsic growth rate, birth rate, and age composition of a stable population to arbitrary marginal changes in its age patterns of fertility and mortality. It uses it also to obtain expressions for the transient response of the age composition of a nonstable population to time-varying changes in the birth sequence, and to age-specific fertility and mortality patterns that change over time. The problem of "bias" in period vital rates is also looked at.

Adult↗
PubMed2000

Anthropological cybernetic model of demography of the island of Hvar.

Intentions of the present investigation were to apply a cybernetic model in description of demography on the island of Hvar for a time period from year 1800 till now. The basic idea of the model applied in this anthropological study (LOPI) is that the rate of reproduction is given by the non-linear controller: Y2/Te(1-(Y3/G)). Constant G represents an environmental carrying capacity of a community with respect to the cohort of older people (no longer a part of the pool of reproductive inhabitants; Y3) sharing limited survival resources. The proportional constant 1/Te connected with the pool of reproductive inhabitants (Y2) correspond to the reproduction maximum. The consistency of the model is evaluated through comparison between model data and census. The LOPI model describes incredibly well the demography of the island of Hvar from the year 1800 till 1940. After year 1950 there were more inhabitants on the island then the model would predict. This fact is connected with changes in the migration or also in the increased carrying capacity (G). On the basis LOPI model, population dynamic oscillates in its development. The example of the island of Hvar has proved that population reaches a maximal number of inhabitants every 200 years. The oscillation of population dynamics is influenced by the migration processes. The mere fact that oscillating population size is connected to population genetics and probably also to sociocultural factors suggests that a cybernetics demographic model can be a guide in the holistic anthropological approach.

Adult↗
PubMed2003

Molecular population genetics of inducible antibacterial peptide genes in Drosophila melanogaster.

Insects respond to septic infection in part by producing a suite of antimicrobial peptides that may be subject to host-pathogen coevolutionary dynamics. In order to infer population genetic forces acting on Drosophila antibacterial peptide genes, we examine global properties of polymorphism and divergence in the Drosophila melanogaster defensin, drosocin, metchnikowin, attacin C, diptericin A, and cecropin A, B, and C genes. As a functional class, antibacterial peptides exhibit low levels of interspecific amino acid divergence. There are multiple amino acid polymorphisms segregating within D. melanogaster, however, a high proportion of which change the charge or polarity of the variable residue. These polymorphisms are particularly prevalent in processed signal and propeptide domains. We find that models of coevolutionary "arms races" and selectively maintained hypervariability do not adequately describe the population dynamics of mature antibacterial peptides in D. melanogaster, but that a highly significant excess of high-frequency derived polymorphisms coupled with substantial intralocus linkage disequilibrium suggests that positive selection may act on antibacterial peptide genes. Some attributes of the data may be consistent with a simple demographic model of population founding followed by expansion, but departures from the equilibrium null tend to be more pronounced in the peptide genes than at other loci around the genome.

Amino Acid Sequence↗
PubMed2003

A model of aging and a shape of the observed force of mortality.

A probabilistic model of aging is considered. It is based on the assumption that a random resource, a stochastic process of aging (wear) and the corresponding anti-aging process are embedded at birth. A death occurs when the accumulated wear exceeds the initial random resource. It is assumed that the anti-aging process decreases wear in each increment. The impact of environment (lifestyle) is also taken into account. The corresponding relations for the observed and the conditional hazard rate (force of mortality) are obtained. Similar to some demographic models, the deceleration of mortality phenomenon is explained via the concept of frailty. Simple examples are considered.

Aged↗
PubMed1995

Probing the evolution of senescence in Drosophila melanogaster with P-element tagging.

Natural populations host a wealth of genetic variation in longevity and age-specific schedules of reproduction. This variation provides critical information for inferring the evolutionary origin of senescence. Patterns of mutational effects on age-specific fecundity and survival provide additional insight to distinguish alternative models of senescence. In this study, P-elements bearing the white minigene were inserted at random into a common genetic background, generating lines of D. melanogaster with single, stable transposon inserts. A series of 48 single-P-element lines revealed statistically significant heterogeneity in both longevity and fecundity. Longevity and early fecundity were only weakly positively correlated (r = 0.286, P = 0.0398). Both the pooled sample and 30 of the individual lines exhibited a leveling of age-specific mortality at advanced ages, in opposition to the classical demographic models. To the extent that these mutational effects are representative of naturally-occurring mutations in heterogeneous populations, this result presents a problem for the evolutionary theory of senescence. Natural selection is inefficient at removing deleterious mutations that are expressed only at late ages, and selection may not differentiate between mutations whose effects on longevity are post-reproductive. A leveling of the mortality rate would also be seen if mutations whose expression is delayed until very late simply do not occur. A simulation of mutation-selection balance among the 48 P-element tagged lines shows that the mean longevity declines monotonically with increasing mutation rate, consistent with the mutation-accumulation model.

Aging↗
PubMed2001

Estimating recombination rates from population genetic data.

We introduce a new method for estimating recombination rates from population genetic data. The method uses a computationally intensive statistical procedure (importance sampling) to calculate the likelihood under a coalescent-based model. Detailed comparisons of the new algorithm with two existing methods (the importance sampling method of Griffiths and Marjoram and the MCMC method of Kuhner and colleagues) show it to be substantially more efficient. (The improvement over the existing importance sampling scheme is typically by four orders of magnitude.) The existing approaches not infrequently led to misleading results on the problems we investigated. We also performed a simulation study to look at the properties of the maximum-likelihood estimator of the recombination rate and its robustness to misspecification of the demographic model.

Genetics, Population↗
PubMed2006

A discriminative prediction model of neurological outcome for patients undergoing surgery of brain arteriovenous malformations.

BACKGROUND AND PURPOSE: To develop and validate a discriminative model for predicting neurological morbidity after brain arteriovenous malformation (bAVM) surgery. METHODS: Of 233 consecutive, prospectively enrolled patients undergoing bAVM surgery, the first 175 were used to derive, and the last 58 to validate, the prediction model. Demographic and angiographic factors were related to modified Rankin Scale scores assigned before, within 72 hours, at 7 days and at > or =1 year after surgery to seek predictors of postoperative neurological deficits (modified Rankin Scale score > or =3). These factors included nidus size, eloquence, venous drainage, diffuseness, white matter configuration, arterial perforator supply and associated aneurysms. RESULTS: Brain eloquence, diffuse nidus and deep venous drainage were significant predictors of early disabling neurological deficits (odds ratios of 4.33, 3.49 and 2.38, respectively). The rounded odds ratios form a weighted 9-point prediction model (maximum scores for eloquence+diffuseness+deep drainage=4+3+2). The score discriminated the probability of experiencing both early (first week) and permanently (at > or =1 year) disabling neurological deficits as follows: 0 to 2: 1.8%, 3 to 5: 17.4%, 6 to 7: 31.6%, >7: 52.9% for early and 0 to 2: 1.8%, 3 to 5: 4.4%, 6 to 7: 18.4%, >7: 32.4% for permanently disabling outcomes. The discrimination of the model was 0.80 with 2.8% optimism. Validation in the second patient cohort revealed good performance at risk stratification. CONCLUSIONS: Relative weights assigned to brain eloquence, diffuse nidus morphology and deep venous drainage of a bAVM provide a simple and discriminative prediction model for neurological outcome after bAVM surgery.

Adolescent↗
PubMed2002

Dynamic effects of predators on cyclic voles: field experimentation and model extrapolation.

Mechanisms generating the well-known 3-5 year cyclic fluctuations in densities of northern small rodents (voles and lemmings) have remained an ecological puzzle for decades. The hypothesis that these fluctuations are caused by delayed density-dependent impacts of predators was tested by replicated field experimentation in western Finland. We reduced densities of all main mammalian and avian predators through a 3 year vole cycle and compared vole abundances between four reduction and four control areas (each 2.5-3 km(2)). The reduction of predator densities increased the autumn density of voles fourfold in the low phase, accelerated the increase twofold, increased the autumn density of voles twofold in the peak phase, and retarded the initiation of decline of the vole cycle. Extrapolating these experimental results to their expected long-term dynamic effects through a demographic model produces changes from regular multiannual cycles to annual fluctuations with declining densities of specialist predators. This supports the findings of the field experiment and is in agreement with the predation hypothesis. We conclude that predators may indeed generate the cyclic population fluctuations of voles observed in northern Europe.

Animals↗
PubMed1996

Prognostic factors for functional outcome of total knee replacement: a prospective study.

BACKGROUND: The objective was to investigate whether baseline physical functioning, medical, psychosocial, or demographic variables predict functional outcome in patients undergoing total knee replacement. METHODS: A prospective cohort study was performed between December 1991 and August 1993. Consecutive, unilateral tricompartmental total knee replacement patients aged > or = 55 yr with osteoarthritis, who met criteria, were enrolled and evaluated one month before and 3 months after total knee replacement. The primary outcome measure was the Medical Outcome Study 36 Item Short Form Health Survey (known as the SF36) Physical Functioning Scale score. The outcome evaluator was not involved in patient care. RESULTS: A hierarchical multiple regression analysis was performed to calculate the contribution of baseline variables to TKR outcome. Of the 27% of outcome variance explained by the model, demographic variables accounted for 4%, psychosocial variables (motivation, role functioning-emotional, and social functioning) for 19% (p = .013), medical variables (previous reconstruction, comorbidity, body mass index, bodily pain) for 2%, and baseline physical function for 2%. CONCLUSIONS: Psychosocial variables are significantly related to total knee replacement functional outcome. Assessment of baseline psychological and social functioning may identify a subset of patients at risk for worse outcome. Specific interventions for these patients should be developed and evaluated as components of patient management prior to and after the procedure.

Activities of Daily Living↗
PubMed1999

The urology work force in Ontario for the 21st century: feast or famine?

OBJECTIVE: To address the issues of work-force planning and modelling in the 21st century for the specialty of urology in the Province of Ontario. DESIGN: Data (from 1991 to 1995) regarding urology physician resources were gathered from Health Canada, the Royal College of Physicians and Surgeons of Canada, the Ontario Physician Human Resources Data Centre, the Canadian Post-M.D. Education Registry, the System for Health Area Resource Planning (SHARP) database, the Canadian Institute for Health Information and the National Physician Database. Specifically, the age and gender breakdown of currently active Ontario urologists, measures of urologist clinical activity (from Ontario Hospital Insurance Plan billings and questionnaires), inputs into and exits from the active urologist population were gathered, and estimates of future needs for urologist services, based on current population and demographic models, were made. A model to predict the balance between future needs for urology services and future supply of urologists was then created and validated against data drawn from the SHARP database. RESULTS: The model revealed that there will be a significant shortage of urologists in Ontario in the immediate and long-term future; by the year 2010 there will be a shortfall of 101 urologists in Ontario, or 51% of the total needed. CONCLUSIONS: Enlarging the urology training programs in Ontario would help to minimize the estimated shortfall. Systematic modelling of physician work-force needs for the future is necessary for the optimal allocation of health care resources. The methodology of the urology work-force model is generalizable to physician work-force planning for other specialty groups on a provincial or national basis.

Computer Simulation↗
PubMed2006

TESD: a transposable element dynamics simulation environment.

UNLABELLED: Various mathematical models have been used to explore the dynamics of transposable elements (TEs) within their host genomes. However, numerous factors can influence their dynamics, and we know only little about the dynamics of TEs when they first began to invade populations. In addition, the influence of population structuring has only recently been investigated. Transposable Element Simulator Dynamics, a population genomics simulation environment, has therefore been developed to provide a simple tool for analyzing the dynamics of TEs in a community based on (i) various TE parameters, such as the transposition and excision rates, the recombination rate and the coefficient of selection against TE insertions; and (ii) population parameters, such as population size and migration rates. The simulations can be used to illustrate the dynamic fate of TEs in structured populations, can be extended by using more specific molecular or demographic models, and can be useful for teaching population genetics and genomics. AVAILABILITY: TESD is distributed under GPL from the Pôle Bioinformatique Lyonnais (PBIL) web server at http://pbil.univ-lyon1.fr/software/TESD

Algorithms↗
PubMed1985

Larval settlement rate: A leading determinant of structure in an ecological community of the marine intertidal zone.

Field studies demonstrate that the population structure of the barnacle Balanus glandula differs between locations of high and low larval settlement rate. These observations, together with results from a model for the demography of an open, space-limited population, suggest that the settlement rate may be a more important determinant of rocky intertidal community structure than is presently realized. Locations with a low larval settlement rate exhibit a generally low abundance of barnacles that varies slightly within years and greatly between years, reflecting yearly differences in settlement. Locations with a high-settlement rate exhibit a generally high abudance of barnacles. However, the abundance varies greatly within years with a significant oscillatory component (period, 30 weeks) and only slightly between years regardless of yearly differences in settlement. At the low-settlement location mortality of barnacles is independent of the area occupied by barnacles. At the high-settlement location mortality is cover-dependent due to increased predation by starfish on areas of high barnacle cover. In both locations the cover-independent component of mortality does not vary with age during the first 60 weeks. As assumed in the demographic model, the kinetics of larval settlement can be described as a process in which the rate of settlement to a quadrat is proportional to the fraction of vacant space within the quadrat. Generalizations that the highest species diversity in a rocky intertidal community is found at locations of intermediate disturbance, and that competition causes zonation between species of the barnacle genera Balanus and Chthamalus, seem to apply only to locations with high-settlement rates.

Journal Article↗
PubMed2024

Rapid vertebrate speciation via isolation, bottlenecks, and drift.

Speciation is often driven by selective processes like those associated with viability, mate choice, or local adaptation, and "speciation genes" have been identified in many eukaryotic lineages. In contrast, neutral processes are rarely considered as the primary drivers of speciation, especially over short evolutionary timeframes. Here, we describe a rapid vertebrate speciation event driven primarily by genetic drift. The White Sands pupfish (Cyprinodon tularosa) is endemic to New Mexico's Tularosa Basin where the species is currently managed as two Evolutionarily significant units (ESUs) and is of international conservation concern (Endangered). Whole-genome resequencing data from each ESU showed remarkably high and uniform levels of differentiation across the entire genome (global FST ≈ 0.40). Despite inhabiting ecologically dissimilar springs and streams, our whole-genome analysis revealed no discrete islands of divergence indicative of strong selection, even when we focused on an array of candidate genes. Demographic modeling of the joint allele frequency spectrum indicates the two ESUs split only ~4 to 5 kya and that both ESUs have undergone major bottlenecks within the last 2.5 millennia. Our results indicate the genome-wide disparities between the two ESUs are not driven by divergent selection but by neutral drift due to small population sizes, geographic isolation, and repeated bottlenecks. While rapid speciation is often driven by natural or sexual selection, here we show that isolation and drift have led to speciation within a few thousand generations. We discuss these evolutionary insights in light of the conservation management challenges they pose.

Animals↗
PubMed2004

Who wants to enter a long-term care facility in a rapidly aging non-Western society? Attitudes of older Koreans toward long-term care facilities.

To estimate future demand for institutional long-term care (LTC) by Koreans, the intention to use LTC facilities was estimated, and the underlying influencing factors were explored. Data from the Korean National Survey of LTC Need in the Elderly compiled in 2001 were used, and 1,850 people aged 65 and older who were classified as the targets for LTC in the survey and for whom complete data were available were sampled. The following influencing variables were selected based on Anderson's service-use model: demographics, social structural factors, family and community resources, and felt and assessed needs. The result shows that, of all the participants, 18.8% intended to use LTC facilities. A stronger intention was related to younger age, Christian religion, fewer children, lower family income, higher chronic comorbidity, and more education. The rapid industrialization of Korea has lead to a transition from the traditional family-centered mode of caregiving to a nontraditional one, but the intention to use LTC facilities is still lower than in Western developed countries. Regarding family resources, the effect of extended families comprising three or more generations is not as significant as expected, but children continue to be regarded as the main resources for LTC. The recent introduction of nontraditional religions to Korea has had a positive effect on intention to use LTC facilities, suggesting that cultural factors influence their use.

Aged↗
PubMed2006

Predictors of caregiver unawareness and nontreatment of dementia among residents of assisted living facilities: the Maryland Assisted Living Study.

OBJECTIVE: Assisted living (AL) is a rapidly expanding residential option for the senior population. With increased utilization, it becomes important to understand the detection and treatment of dementia in this setting, but little is known. The objective of this study was to identify and evaluate factors associated with caregiver unawareness of dementia and failure to treat dementia in AL. METHODS: The setting was a cross-sectional study of a random sample of AL facilities in central Maryland (The Maryland Assisted Living Study). Geriatric psychiatrists evaluated 198 participants and assigned dementia diagnoses to 134 residents (67.7%). The extent to which dementia was recognized and treated in these facilities was estimated on the basis of caregiver interview and chart review data. Using logistic regression models, demographic, cognitive, and functional measures were evaluated as predictors of caregiver unawareness and nontreatment of dementia. RESULTS: Severity of cognitive and functional impairment, number of neuropsychiatric symptoms, and male gender were all independent predictors of caregiver unawareness of dementia. Family and caregiver unawareness of dementia and female gender were predictors of failure to treat dementia. Detection and treatment were not associated with race, age, or overall medical health. CONCLUSIONS: Caregivers were more likely to be unaware of dementia in residents who did not have severe cognitive impairment or obvious behavioral and functional problems. Caregiver and family unawareness were in turn associated with nontreatment. Observed gender differences in detection and treatment will require replication and further study. These observations suggest that systematic educational interventions for caregivers and families may improve detection and hence treatment in the AL setting.

Aged↗
PubMed1999

Looking into the demography of an iron age population in the western Mediterranean. I. Mortality.

In this paper, we attempt to reconstruct the mortality pattern of the population buried in S'Illot des Porros (Majorca), an Iron Age necropolis in the western Mediterranean, by means of paleodemographic analysis. The skeletal sample consists of 285 individuals, 93 subadults (under 20 years old) and 192 adults. The aim of this study is twofold: first, to identify and to evaluate the structural anomalies of the skeletal sample, and second, to obtain a possible and realistic description of the biological dynamics of this population, with special reference to its mortality pattern. The study uses current demographic methodology and several demographic models (for comparison). An abridged life table was built to estimate the mortality parameters. To evaluate the likelihood of the estimated data, an indirect analysis, which consisted of a comparison of our results with different population models (Weiss [1973] American Antiquity 38; Coale and Demeny [1996] Regional Model Life Tables and Stable Populations. Princeton: Princeton University Press; Ledermann [1969] Nouvelles tables-types de mortalité. Paris: Presses Universitaires de France), was carried out. An important bias was identified in the case of children, mostly affecting infants but also children between the ages of 1 and 5. This was interpreted as a census error due to taphonomic reasons and to an excluding differential funeral rite. A life expectancy at birth of approximately 28 years was estimated from the observed data. When this bias was removed, the estimated life expectancy at birth dropped to 23 years. The use of the Brass logit system allowed us to sketch a possible mortality profile for this population: low life expectancy, high infant mortality and hard life conditions, which were the cause of the low levels of survivorship in old ages. Am J Phys Anthropol 110:285-301, 1999.

Adolescent↗
PubMedDate not supplied

Characteristics of patients adhering to a hospital's no-smoking policy.

OBJECTIVES: The purpose of this paper is to examine the characteristics of smokers who adhere to a hospital smoking ban, compared to those who do not. DESIGN: The data presented in this paper are baseline and discharge survey data collected among hospitalized smokers. SETTING: This study was conducted in two teaching hospitals in a northeastern city. PATIENTS/PARTICIPANTS: The subjects were 358 smokers who participated in a larger smoking intervention trial. MAIN RESULTS: Seventy-six percent of the subjects reported adhering to the smoke-free policy during their hospital stay. In a multivariate model, demographic factors that predicted adherence included being older, having shorter length of stay, not reporting recreational drug use in the previous 12 months, and not having alcohol-related problems. Smoking history variables that predicted adherence included having had at least 24 h of abstinence in the 7 days prior to hospitalization; self-efficacy variables (e.g., confidence in ability to quit smoking in 1 month and less anticipated difficulty refraining from smoking during hospitalization) also predicted adherence. CONCLUSIONS: Understanding the factors that predict adherence to health care policies can provide useful information for health promotion interventions in a medical setting. The implications of these findings are discussed.

Age Factors↗