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Results for “Demographic modelling”

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PubMed2003

Predictability of prescription drug expenditures for Medicare beneficiaries.

MCBS data are used to analyze the predictability of drug expenditures by Medicare beneficiaries. Predictors include demographic characteristics and measures of health status, the majority derived using CMS' diagnosis cost group/hierarchical condition category (DCG/HCC) risk-adjustment methodology. In prospective models, demographic variables explained 5 percent of the variation in drug expenditures. Adding health status measures raised this figure between 10 and 24 percent of the variation depending on the model configuration. Adding lagged drug expenditures more than doubled predictive power to 55 percent. These results are discussed in the context of forecasting, and risk adjustment for the proposed new Medicare drug benefit.

Aged↗

PubMed2025

Pleistocene island connectivity did not enhance dispersal or impact population size change in Galápagos geckos.

Patterns of biodiversity on remote archipelagos are largely shaped by intra-archipelago colonization followed by in situ diversification. Pleistocene sea-level fluctuations purportedly enhanced gene flow among terrestrial organisms by increasing connectivity during periods of lower sea level. Furthermore, changes in sea-level are hypothesized to impact population sizes as a result of fluctuations in island sizes. Here, we used genomic data to test the role of Pleistocene island connectivity on the diversification and demographics of leaf-toed geckos (Phyllodactylus) endemic to the Galápagos. Consistent with previous studies, we found that present diversity of Galápagos Phyllodactylus stems from three independent dispersal events. Contrary to the hypothesis of Pleistocene-driven diversification, we found no correspondence between lineage divergence and island connectivity. Furthermore, we found no evidence of introgression; demographic modelling indicated that all species increased rapidly in effective population size in the period 20-150 ka, and these inferred demographic expansions were largely asynchronous and apparently unassociated with species or island age. Collectively, these results indicate that more complex abiotic and/or biotic factors may better explain the recent demographic history of Phyllodactylus and underscore the need for additional population genomic studies of terrestrial taxa to understand the impact of past climate cycles on Galápagos island communities.

Animals↗

PubMed2003

Which future for the French Pyrenean brown bear (Ursus arctos) population? An approach using stage-structured deterministic and stochastic models.

The Pyrenean brown bear (Ursus arctos) population is considered as one of the most seriously threatened with extinction in Western Europe. To assess its viability and possible needs of augmentation, we develop deterministic and stochastic stage-structured demographic models. The deterministic model reveals that a bear population cannot have a high annual growth rate and is particularly sensitive to breeder survival. High demographic parameters appear to be crucial to population persistence, especially for a small population that remains vulnerable to demographic and environmental stochasticities. The Pyrenean population cannot therefore be considered as viable. Successful conservation strategies for this population would require releasing more bears in both sub-populations in the near future.

Animals↗

PubMed2004

Modelling transmission, immunity and disease of Haemophilus influenzae type b in a structured population.

An individual-based stochastic simulation model was constructed to study the epidemiology of Haemophilus influenzae type b (Hib) transmission, immunity and invasive disease. Embedded in a demographic model, the transmission model of Hib carriage employs the most important social mixing patterns with three types of contact sites (family, day-care group, and school class). The model includes immunity against invasive Hib disease, initiated and boosted by Hib carriage and cross-reactive bacterial encounters. The model reproduces the observed age patterns in Hib carriage and disease in Finland before large-scale use of the Hib conjugate vaccines. The model was used to investigate characteristics of Hib transmission. The analysis emphasizes transmission between children and adults in families while pointing out the importance of pre-school and school-aged children in maintaining Hib circulation. Carriage in these age groups is thus identified as being essential to target for sustained effects of interventions by vaccination.

Adolescent↗

PubMed2000

A genome-wide departure from the standard neutral model in natural populations of Drosophila.

We analyze nucleotide polymorphism data for a large number of loci in areas of normal to high recombination in Drosophila melanogaster and D. simulans (24 and 16 loci, respectively). We find a genome-wide, systematic departure from the neutral expectation for a panmictic population at equilibrium in natural populations of both species. The distribution of sequence-based estimates of 2Nc across loci is inconsistent with the assumptions of the standard neutral theory, given the observed levels of nucleotide diversity and accepted values for recombination and mutation rates. Under these assumptions, most estimates of 2Nc are severalfold too low; in other words, both species exhibit greater intralocus linkage disequilibrium than expected. Variation in recombination or mutation rates is not sufficient to account for the excess of linkage disequilibrium. While an equilibrium island model does not seem to account for the data, more complicated forms of population structure may. A proper test of alternative demographic models will require loci to be sampled in a more consistent fashion.

Animals↗

PubMed1996

Linkage disequilibrium analysis in young populations: pseudo-vitamin D-deficiency rickets and the founder effect in French Canadians.

Pseudo-vitamin D-deficiency rickets (PDDR) was mapped close to D12S90 and between proximal D12S312 and distal (D12S305, D12S104) microsatellites that were subsequently found on a single YAC clone. Analysis of a complex haplotype in linkage disequilibrium (LD) with the disease discriminated among distinct founder effects in French Canadian populations in Acadia and in Charlevoix-Saguenay-Lac-Saint-Jean (Ch-SLSJ), as well as an earlier one in precolonial Europe. A simple demographic model suggested the historical age of the founder effect in Ch-SLSJ to be approximately 12 generations. The corresponding LD data are consistent with this figure when they are analyzed within the framework of Luria-Delbrück model, which takes into account the population growth. Population sampling due to a limited number of first settlers and the rapid demographic expansion appear to have played a major role in the founding of PDDR in Ch-SLSJ and, presumably, other genetic disorders endemic to French Canada. Similarly, the founder effect in Ashkenazim, coinciding with their early settlement in medieval Poland and subsequent expansion eastward, could explain the origin of frequent genetic diseases in this population.

Base Sequence↗

PubMed2003

A re-examination of levels and differential in fertility in South Africa from recent evidence.

The final estimate of South Africa's population as of October 1996 from the first post-apartheid census by Statistics South Africa was lower (40.6 million) than expected (42 million). The expectation of a total population of 42 million was largely based on results of apartheid projections of South Africa's population. The results of the last apartheid census in South Africa in 1991 had been adjusted such that it was consistent with results modelling the population size of South Africa. The discrepancy between the final estimate of the 1996 census and that expected from the modelling described above, and the departure by Statistics South Africa from previous practice of adjusting the census results to be consistent with demographic models, has generated controversies regarding the accuracy of the final results from the 1996 census. This study re-examines levels and differential in fertility in South Africa from recent evidence in order to assess whether or not the fertility inputs in projections of South Africa's population during the apartheid era overestimated fertility.

Adolescent↗

PubMed2004

A comparison of self-reported energy intake with total energy expenditure estimated by accelerometer and basal metabolic rate in African-American women with type 2 diabetes.

OBJECTIVE: This study assesses the validity of dietary data from African-American women with type 2 diabetes by comparing reported energy intake (EI) with total energy expenditure (TEE) estimated by an accelerometer and basal metabolic rate (BMR). RESEARCH DESIGN AND METHODS: EI of 200 African-American women was assessed by three telephone-administered 24-h diet recalls using a multiple-pass approach. Physical activity was measured over a 7-day period by accelerometer, which also provided an estimate of TEE. Underreporting of EI was determined by using cutoffs for EI-to-TEE and EI-to-BMR ratios. RESULTS: Participants, on average, were 59 years of age, with a BMI of 35.7, 10.5 years of diagnosed diabetes, and 10.7 years of education. Mean EI was 1,299 kcal/day; mean EI-to-TEE and EI-to-BMR ratios were 0.65 and 0.88, respectively. Among the 185 subjects with complete dietary data, 81% (n=150) were classified as energy underreporters using the EI-to-TEE ratio cutoff; 58% (n=107) were classified as energy underreporters using the EI-to-BMR ratio. Energy underreporters had significantly lower reported fat, higher protein, but similar carbohydrate intakes compared with non-underreporters. The EI-to-TEE ratio was not significantly associated with any demographic variables or following a diet for diabetes, but it was inversely associated with BMI (r=-0.37, P<0.0001). In a multivariate model, demographic variables, BMI, and following a diet for diabetes explained 16% of the variance in the EI-to-TEE ratio, with the latter two variables being the only significant predictors (inversely associated). CONCLUSIONS: Widespread energy underreporting among this group of overweight African-American women with type 2 diabetes severely compromised the validity of self-reported dietary data.

Black or African American↗

PubMed1988

[The induced demographic impact of interprovincial migration in Canada, 1976-1981].

"Migration is much more than a simple transfer of individuals from one region to another.... It also implies a transfer of 'years to be lived' and 'children to be born'. Rogers' multidimensional demographic model allows one to measure such an induced impact. The results obtained show that, in the case of interprovincial migration in Canada, this induced impact is far from being proportional to the direct impact in terms of individuals transferred." (SUMMARY IN ENG)

Americas↗

PubMed2006

Perfect simulation from nonneutral population genetic models: variable population size and population subdivision.

We show how the idea of monotone coupling from the past can produce simple algorithms for simulating samples at a nonneutral locus under a range of demographic models. We specifically consider a biallelic locus and either a general variable population size mode or a general migration model for population subdivision. We investigate the effect of demography on the efficacy of selection and the effect of selection on genetic divergence between populations.

Algorithms↗

PubMedDate not supplied

Evolutionary patterns among measures of aging.

Maximum lifespan has been one of the most common aging measures in comparative studies, while the Gompertz model has recently attracted both proponents and critics of its capacity to adequately describe the acceleration of mortality in the oldest age classes. The Gompertz demographic model describes age-dependent mortality rate acceleration and age-independent mortality using the parameters alpha and A, respectively. Evolutionary biologists have predominantly used average longevity in studies of aging. Little is known about the evolutionary relationships of these measures on the microevolutionary time scale. We have simultaneously compared Gompertz parameters, average longevity, and maximum longevity in 50 related populations of Drosophila melanogaster, many of which have been selected for postponed aging. Overall, these populations have differentiated significantly for the A and alpha parameter of the Gompertz equation, as well as average and maximum longevity. These indices of aging appear to measure the same genetic changes in aging. However, in some specific population comparisons, the relationships among these measures are more complex. In a second experiment, environmental manipulation of longevity had substantially different effects from genetic differentiation, with the A parameter accounting for changes in overall mortality. The adequacy of the maximum lifespan and the Gompertz equation as indices of aging in evolutionary studies is discussed.

Aging↗

PubMed1992

Stochastic demographic forecasting.

"This paper describes a particular approach to stochastic population forecasting, which is implemented for the U.S.A. through 2065. Statistical time series methods are combined with demographic models to produce plausible long run forecasts of vital rates, with probability distributions. The resulting mortality forecasts imply gains in future life expectancy that are roughly twice as large as those forecast by the Office of the Social Security Actuary.... Resulting stochastic forecasts of the elderly population, elderly dependency ratios, and payroll tax rates for health, education and pensions are presented."

Adult↗

PubMed1996

Gastroenterology workforce modeling.

OBJECTIVE: To examine the current supply and distribution of gastroenterologists and project future supply under various scenarios to provide a paradigm for workforce reform. DESIGN: An analysis of current practices and distribution of gastroenterologists and a demographic model, using the 1992 gastroenterology workforce as a baseline. MAIN OUTCOME MEASURE: Comparison of current supply, distribution, and practice profiles with past data and future projections, using analyses of data from the 1993 Area Resource File, 1992 Medicare Part B file, age- and sex-specific death and retirement rates from the Bureau of Health Professions, managed care staffing patterns, the National Survey of Internal Medicine Manpower, and the Bureau of the Census. RESULTS: Rapid growth in the number of US gastroenterologists has resulted in a gastroenterologist-to-population ratio double that used on average by health maintenance organizations. In addition, the work profile of gastroenterologists is shared significantly by primary care physicians and other specialists, with the exception of a few specific and uncommon procedures. CONCLUSIONS: Empirical evidence suggests that, even in the absence of detailed models to describe the desired supply/need balance for gastroenterology, the US health care system and clinicians may benefit from a reduction in gastroenterology training programs. The Gastroenterology Leadership Council endorsed a goal of 25% to 50% reduction in trainee numbers over 5 years, and recent National Resident Matching Program data indicate that a voluntary downsizing process is in full force. This study illustrates a paradigm for workforce planning that could be useful for other medical specialties.

Demography↗

PubMed2003

Life-history models of extinction: a test with island spiders.

This study analyzes extinction patterns for two species of orb spiders monitored annually on 77 islands over a continuous 20-yr period. One species, Argiope argentata, has large populations sometimes crashing quickly to extinction and a much weaker relation of extinction likelihood to population size than does the other species, Metepeira datona. Demographic models were built for both species and matched against observations. Differences between the species in life-history traits-estimated with measurements from the field-together with incorporation of demographic stochasticity, a population ceiling, and environmental stochasticity, were necessary to fit the observed extinction curves. As predicted from life-history patterns, long-term population growth rates (and hence predicted extinction probabilities) are relatively very sensitive to values of juvenile survivorship. Models are also sensitive to variation in the population ceiling and environmental noise, which tend to act in a complementary manner. A simple model with no age structure was able to fit the data on large initial population sizes but not on small initial population sizes, showing that life cycle characteristics interact with the various sources of stochasticity and hence have to be taken into account to produce a precise model of the extinction process.

Age Factors↗

PubMed2006

Extreme patterns of variance in small populations: placing limits on human Y-chromosome diversity through time in the Vanuatu Archipelago.

Small populations are dominated by unique patterns of variance, largely characterized by rapid drift of allele frequencies. Although the variance components of genetic datasets have long been recognized, most population genetic studies still treat all sampling locations equally despite differences in sampling and effective population sizes. Because excluding the effects of variance can lead to significant biases in historical reconstruction, variance components should be incorporated explicitly into population genetic analyses. The possible magnitude of variance effects in small populations is illustrated here via a case study of Y-chromosome haplogroup diversity in the Vanuatu Archipelago. Deme-based modelling is used to simulate allele frequencies through time, and conservative confidence bounds are placed on the accumulation of stochastic variance effects, including diachronic genetic drift and contemporary sampling error. When the information content of the dataset has been ascertained, demographic models with parameters falling outside the confidence bounds of the variance components can then be accepted with some statistical confidence. Here I emphasize how aspects of the demographic history of a population can be disentangled from stochastic variance effects, and I illustrate the extreme roles of genetic drift and sampling error for many small human population datasets.

Alleles↗

PubMed1995

Projections of housing disruption among adults with mental illness who live with aging parents.

OBJECTIVE: The need to plan for the future housing needs of adults with serious mental illness who reside with aging parents is an issue of increasing importance to mental health policy makers as well as family members. This study provides estimates of the number of adults with severe and persistent mental illness in New York State who could be expected to experience housing disruption because of their parents' death. METHODS: Demographic modeling methods were applied to data from a variety of sources, including surveys of mentally ill adults receiving public mental health services in New York State and demographic statistics on the general state population. RESULTS: An estimated 13,400 to 49,600 adults with severe and persistent mental illness who receive services from the public mental health system in New York State reside with one or both parents. Within this group, between 300 and 1,200 adults could have been expected to experience housing disruption due to parental death each year between 1990 and 1994. Demographic trends indicate that through 2009, these disruptions will increase at a faster rate than growth in the state's general adult population. CONCLUSIONS: Additional housing with mental health supports and other programs will be needed to accommodate the growing number of severely mentally ill adults whose housing may be disrupted because of the death of their parents.

Adolescent↗

PubMed2005

Predictors of sexual transmission risk behaviors among HIV-positive young men.

Reduction in the incidence of high-risk sexual behaviors among HIV-positive men is a priority. We examined the roles of proximal substance use and delinquency-related variables, and more distal demographic and psychosocial variables as predictors of serious high-risk sexual behaviors among 248 HIV-positive young males, aged 15-24 years. In a mediated latent variable model, demographics (ethnicity, sexual orientation and poverty) and background psychosocial factors (coping style, peer norms, emotional distress, self-esteem and social support) predicted recent problem behaviors (delinquency, common drug use and hard drug use), which in turn predicted recent high-risk sexual behaviors. Hard drug use and delinquency were found to predict sexual risk behaviors directly, as did lower self-esteem, white ethnicity and being gay/bisexual. Negative peer norms strongly influenced delinquency and substance use and positive coping predicted less delinquency. In turn, less positive coping and negative peer norms exerted indirect effects on sexual transmission risk behavior through delinquency and hard drug use. Results suggest targeting hard drug use, delinquency, maladaptive peer norms, dysfunctional styles of escaping stress and self-esteem in the design of intervention programs for HIV-positive individuals.

Adolescent↗

PubMed2005

Geographical distance and physical barriers shape the genetic structure of Eurasian red squirrels (Sciurus vulgaris) in the Italian Alps.

Red squirrels (Sciurus vulgaris) are widely distributed throughout Eurasia, occurring in many types of coniferous and mixed-deciduous forests. In fragmented landscapes, small and partly isolated populations with low immigration rates show reduced genetic diversity, but reforestation can increase gene flow and restore levels of genetic variation in a few decades. No studies have so far investigated the genetic structure of red squirrel in large, continuous forests. The Italian Alps are presently characterized by almost continuous, recently reconnected forest habitats, that were affected by deep landscape changes during last glaciations but remained mostly unchanged between 10 000 and 200 years bp, when forest cover was heavily reduced. In this study we analyse patterns of genetic variability of red squirrels in and between seven sites distributed over 250 km of Alpine habitat, using mitochondrial DNA (mtDNA) and microsatellites. We use isolation-by-distance (IBD) models to investigate the relative importance that past (Pleistocene glaciations) and recent (fragmentation, bottlenecks) events had on the present genetic situation. Both nuclear and mtDNA data indicate a significant differentiation among study sites and a significant correlation between genetic and geographical distance only over a large scale. No recent bottlenecks are recorded through microsatellites and demographic models strongly support equilibrium between gene flow and drift; however, mtDNA suggests that there may have been local demographic crashes, probably in correspondence with the 19th-century forest fragmentation. These findings indicate that local landscape factors other than geographical distance per se, such as barriers of unsuitable habitat, affect gene flow and determine differentiation.

Animals↗