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PubMed1980

The distribution of mutant alleles in a subdivided population.

The results are presented from a simulation study of the spatial distribution of mutant alleles in a subdivided population. Statistical measures of the spatial pattern are defined in such a way that the same quantities could be measured in a geographic survey of allele frequencies in natural populations. Two types of quantities are discussed in this paper: (1) the occupancy distribution provides information on the presence or absence of the mutant in different numbers of demes; and (2) the conditional frequency distribution provides information about the extent of local differentiation when the mutant is present in different numbers of demes. Properties of these distributions are found for different types of natural selection acting on the mutant. Some results are presented for the same statistical measures based on samples of individuals from a fraction of the total number of demes. The simulation results for intermediate levels of the migration rates are compared with analytic results obtained on the limits of high and low migration rates. The main conclusion is that these measures of the spatial distribution of mutants in a subdivided population have simple properties that could provide a new perspective on data from natural populations.

Alleles↗
PubMed1999

Recovery of mutations of different sizes from a population sample of DNA sequences under variable mutation rates across sites.

Mutations may be classified according to their positions of occurrence in the genealogy of the sampled DNA sequences from a population. A mutation is said to be of size i if it has i descendants in the sample. Such classifications for mutations may yield detailed insights into the evolutionary history and properties of the population. Statistical methods based on such classification have been developed and shown to be efficient and powerful. However, the utility of these statistical methods critically depends on reliable and robust recovery of mutations of different sizes. We investigated the distributional changes of mutations of different sizes due to genealogy reconstruction using the unweighted pair-group method with arithmetic mean (UPGMA) and the performance of maximum-parsimony method in inferring mutations of different sizes on a given topology. Genealogy reconstruction by UPGMA was found to change the distribution of mutations of different sizes on constructed topologies. Multiple hits at some nucleotide sites made it difficult to infer mutations of different sizes with the maximum-parsimony method, even when the true topology was designated. These results suggest that while the newly developed statistical methods employing information on mutations of different sites are powerful, they also impose significant new challenges for developing methods to accurately recover mutations of different sizes from population DNA sequence data.

Algorithms↗
PubMed1996

PhenoDB: an integrated client/server database for linkage and population genetics.

In this paper we describe PhenoDB, an Internet-accessible client/server database application for population and linkage genetics. PhenoDB stores genetic marker data on pedigrees and populations. A database for population and linkage genetics requires two core functions: data management tasks, such as interactive validation during data entry and editing, and data analysis tasks, such as generating summary population statistics and performing linkage analyses. In PhenoDB we attempt to make these tasks as easy as possible. The client/server architecture allows efficient management and manipulation of large datasets via an easy-to-use graphical interface. PhenoDB data (73 populations, 34 pedigrees, approximately 4200 individuals, and close to 80,000 typings) are stored in a generic format that can be readily exported to (or imported from) the file formats required by various existing analysis programs such as LIPED and Lathrop and Lalouel's Multipoint Linkage. PhenoDB allows performance of complex ad-hoc queries and can generate reports for use in project management. Finally, PhenoDB can produce statistical summaries such as allele frequencies, phenotype frequencies, and Chi-square tests of Hardy-Weinberg ratios of population/pedigree data.

Alleles↗
PubMed2006

Late Pleistocene divergence and subsequent population expansion of two closely related fish species, Japanese anchovy (Engraulis japonicus) and Australian anchovy (Engraulis australis).

Climatic oscillations during the Pleistocene ice ages produced great changes in species' geographical distribution and abundance, which could be expected to have genetic consequences. Living in the temperate upwelling zones of the northwestern Pacific, Japanese anchovy (Engraulis japonicus) might have been affected by these severe climatic oscillations. To investigate the effects of Pleistocene climatic changes on the evolution in Japanese anchovy, fragments of 522 bp at the 5' end of mitochondrial DNA control region were sequenced for 241 individuals from 13 localities and 37 individuals of Australian anchovy. Japanese anchovy and Australian anchovy are reciprocally monophyletic and a late Pleistocene transequatorial divergence between the two species was indicated. High levels of haplotype diversity (>0.99) were found for all samples, indicating a high level of genetic diversity. Analyses of molecular variance and the conventional population statistic F(ST) revealed no significant genetic structure throughout the range of Japanese anchovy. Both mismatch distribution analyses and neutrality tests suggested a late Pleistocene population expansion for both Japanese anchovy (79,000-317,000 years ago) and Australian anchovy (45,000-178,000 years ago).

Animals↗
PubMed2005

An independent confirmation of a quantitative trait locus for milk yield and composition traits on bovine chromosome 26.

Several reports have demonstrated that bovine chromosome 26 (BTA26) harbours significant or suggestive quantitative trait loci (QTL) for milk production and composition traits in dairy cattle. Our previous study showed that a C/T substitution in the bovine TCF7L2 gene on BTA26 was significantly linked to QTL for protein yield (PY) in a Canadian dairy cattle population. Actually, this polymorphism was one of the markers derived from a genome-wide screening of QTL for milk PY using an amplified fragment length polymorphism technique combined with a DNA pooling strategy. In the present study, 990 Holstein bulls with complete genotype and phenotype data from 14 sire families were analysed to confirm, if the QTL effects exist in other populations. Statistical analysis revealed that this marker was significantly associated with PY, protein percentage, milk yield and fat yield (FY) (p < 0.001) in the US Holstein population. These results indicate that this QTL region has a pleiotrophic effecton different milk traits and is portable in different populations.

Analysis of Variance↗
PubMed2003

Serological researches in the south of Moldavia in connection with the problem of the ethnogeny of the Gagauzes, the Moldavians and the Bulgarians.

With the aid of data of frequencies of genetically determined blood group systems, the authors have tried to show the basic ethno-genetic directional patterns in Southern Moldavia and in the Dniester-Carpathian-Danubian region in its entirety. Blood Groups A1A27B0, RHESUS, MN, and KELL have been determined in six random samples from four Gagauz villages (n = 330), one Moldavian village (n = 101) and one Bulgarian village (n = 96). The analysis of gene frequencies demonstrates genetic homogeneity of the total Gagauz population. Statistically reliable differentiation is observed only for the RHESUS system. It is possible now to suppose that the haemotological types of modern Gagauz and Bulgarian populations have been developed on the basis of the Balcanic serogenetic types, partially transformed under influence of gene flow from probably Central Asian or other eastern centers. The position of the Moldavians on the serogenetic map of Europe is less certain, due to a considerable ambiguity in the allele frequencies of the various blood group systems. Founder effects may account for these observations. However, the genetic distance and cluster analyses carried out on the frequencies of the surveyed blood group systems have shown the affinity of Moldavians with the Romanians and Eastern European populations.

ABO Blood-Group System↗
PubMed2005

Endophthalmitis following cataract surgery in southwest Finland from 1987 to 2000.

PURPOSE: To investigate the incidence, causes, prevention, treatment and outcome of postoperative endophthalmitis (POE) following cataract surgery in southwest Finland from 1987 to 2000. METHODS: We reviewed the medical records of all patients with POE following cataract surgery treated in the hospital district of Southwest Finland from 1 January 1987 to 31 December 2000. Population-based annual incidence rates of cataract extractions and POE were calculated using the corrected population statistics of the hospital district. RESULTS: There were 29,350 cataract procedures during the 14-year period. POE developed in 47 patients. The annual incidence of cataract operations increased more than fivefold from 1987 (155 per 100,000 population) to the maximum in 1999 (930 per 100,000 population), whereas the annual incidence of postcataract endophthalmitis decreased from the maximum of 11.1 per 1,000 cataract extractions (1.91 per 100,000 population) in 1988 to the minimum of 0-0.6 per 1,000 cataract extractions in 1999 and 2000. POE occurred statistically significantly more frequently after extracapsular cataract extraction (ECCE) than after phacoemulsification (Phaco) (P=0.0006). Gram-positive bacteria were the most frequent cause of acute POE and Propionibacterium acnes was the most frequent reason for delayed-onset POE. The complications of POE after cataract surgery included visual loss to below 0.05 (25.5% of affected eyes), opacification of the cornea (21.3%), secondary cataract (40.4%), increase in intraocular pressure (29.8%), vitreous clouding (63.8%), and retinal detachment (6.4%). Nearly one half of the eyes achieved final visual acuity of 0.5 or better. CONCLUSIONS: During the 14-year study period there was a shift from ECCE to Phaco, a fivefold increase in cataract extractions, and a decrease in the annual incidence of POE from 5.5-11.1 to 0-0.6 per 1,000 operations. Phaco was associated with a lower risk of POE than ECCE.

Adult↗
PubMed2006

Demographic change and the future demand for public hospital care in Australia, 2005 to 2050.

BACKGROUND: Over the next 45 years the Australian population will age rapidly as the baby boomer cohort moves into retirement and then old age. As the population ages there will be substantial growth in the demand for hospital bed-days, placing a corresponding demand on infrastructure and staffing. METHODS: Australian Bureau of Statistics population projections to 2050 and Australian Institute of Health and Welfare public hospital bed-day data from 1993-94 to 2003-04 were used to develop models of future demand and examine the sensitivity of the results to model assumptions. RESULTS: Over the long term, demand for public hospital bed-days was projected to grow faster than population growth. By 2050, ageing will increase the demand for bed-days by between 70% and 130% depending on the underlying assumptions, and the proportion of bed-days devoted to older people will increase from under 50% in 2005 to over 70%. CONCLUSIONS: Ageing of the population will increase the demand for health services just as it will become harder to recruit health professionals as the large baby boomer cohort retires from the health workforce. Accordingly, we need to plan now to ensure future needs of the ageing population are met.

Adolescent↗
PubMed1990

Morphological evidence for alveolar recruitment during inflation at high transpulmonary pressure.

The effect of continuous inflation of lungs at 30 cmH2O transpulmonary pressure (Ptp) on air-space size was assessed by chord length-frequency distribution analysis. Lungs from gerbils were excised, allowed to collapse freely, and inflated to 30 cmH2O Ptp in a humidified chamber kept at 37 degrees C. When the lungs appeared fully inflated with no observable pleural surface atelectasis, the left lung was occluded while the right was maintained at 30 cmH2O for 10 min longer and then occluded. During this time, the right lung increased its volume from 70 to 100%. Then both lungs were quick frozen, freeze dried, and embedded in glycol methacrylate, and 1- to 2-microns-thick histological sections cut. Lungs from a control group of gerbils were similarly inflated to 30 cmH2O, both left and right were occluded, the left was quick frozen immediately, and the right was frozen 10 min later. Chord lengths of air spaces from cranial and caudal lobes of lungs were acquired using a Dapple Systems image analyzer, and a two-population frequency distribution was generated for analysis with an IBM PC. The results indicate that the volume increase during continuous inflation at 30 cmH2O Ptp was associated with a shift in the chord length distribution toward the smaller chord lengths. A two-population statistical analysis indicated that the inflation resulted in an increase in the relative proportion of smaller chord lengths, with no increase in the mean of this smaller population. We conclude that continuous inflation at 30 cmH2O Ptp results in alveolar recruitment.

Animals↗
PubMed1987

Utilization prediction for helicopter emergency medical services.

As the number of helicopter emergency medical services (HEMS) programs continues to expand rapidly, the need for an accurate, readily obtainable, inexpensive method of utilization prediction for these services has become apparent. Accurate volume and case mix prediction for these services are increasingly important as financial constraints become more severe. All previous methods of utilization prediction based on experiences of individual services or accident statistics have been either inaccurate, costly, or difficult to obtain in a relatively short period of time. Prediction of HEMS utilization requires consideration of many significant, simultaneous factors, in addition to patient needs based on population statistics. Through use of a survey of all hospital-based helicopter emergency service programs and published census data, this study analyzed factors relating to helicopter program volume and case mix, providing insight as to why previous methods utilizing total population were inaccurate. A more accurate yet simple and inexpensive method of utilization prediction for HEMS was developed.

Aircraft↗
PubMed1997

Artificial neural networks applied to outcome prediction for colorectal cancer patients in separate institutions.

BACKGROUND: Artificial neural networks are computer programs that can be used to discover complex relations within data sets. They permit the recognition of patterns in complex biological data sets that cannot be detected with conventional linear statistical analysis. One such complex problem is the prediction of outcome for individual patients treated for colorectal cancer. Predictions of outcome in such patients have traditionally been based on population statistics. However, these predictions have little meaning for the individual patient. We report the training of neural networks to predict outcome for individual patients from one institution and their predictive performance on data from a different institution in another region. METHODS: 5-year follow-up data from 334 patients treated for colorectal cancer were used to train and validate six neural networks designed for the prediction of death within 9, 12, 15, 18, 21, and 24 months. The previously trained 12-month neural network was then applied to 2-year follow-up data from patients from a second institution; outcome was concealed. No further training of the neural network was undertaken. The network's predictions were compared with those of two consultant colorectal surgeons supplied with the same data. FINDINGS: All six neural networks were able to achieve overall accuracy greater than 80% for the prediction of death for individual patients at institution 1 within 9, 12, 15, 18, 21, and 24 months. The mean sensitivity and specificity were 60% and 88%. When the neural network trained to predict death within 12 months was applied to data from the second institution, overall accuracy of 90% (95% CI 84-96) was achieved, compared with the overall accuracy of the colorectal surgeons of 79% (71-87) and 75% (66-84). INTERPRETATION: The neural networks were able to predict outcome for individual patients with colorectal cancer much more accurately than the currently available clinicopathological methods. Once trained on data from one institution, the neural networks were able to predict outcome for patients from an unrelated institution.

Bias↗
PubMed2000

Statistical analysis of Fisher et al. PBPK model of trichloroethylene kinetics.

Two physiologically based pharmacokinetic models for trichloroethylene (TCE) in mice and humans were calibrated with new toxicokinetic data sets. Calibration is an important step in model development, essential to a legitimate use of models for research or regulatory purposes. A Bayesian statistical framework was used to combine prior information about the model parameters with the data likelihood to yield posterior parameter distributions. For mice, these distributions represent uncertainty. For humans, the use of a population statistical model yielded estimates of both variability and uncertainty in human toxicokinetics of TCE. After adjustment of the models by Markov chain Monte Carlo sampling, the mouse model agreed with a large part of the data. Yet, some data on secondary metabolites were not fit well. The posterior parameter distributions obtained for mice were quite narrow (coefficient of variation [CV] of about 10 or 20%), but these CVs might be underestimated because of the incomplete fit of the model. The data fit, for humans, was better than for mice. Yet, some improvement of the model is needed to correctly describe trichloroethanol concentrations over long time periods. Posterior uncertainties about the population means corresponded to 10-20% CV. In terms of human population variability, volumes and flows varied across subject by approximately 20% CV. The variability was somewhat higher for partition coefficients (between 30 and 40%) and much higher for the metabolic parameters (standard deviations representing about a factor of 2). Finally, the analysis points to differences between human males and females in the toxicokinetics of TCE. The significance of these differences in terms of risk remains to be investigated.

Animals↗
PubMed2005

Complex trait mapping in isolated populations: Are specific statistical methods required?

In this paper, we review the statistical methods that can be used in isolated populations to map genes involved in complex diseases. Our intention is to highlight the fact that if the features of population isolates may help in the identification of susceptibility factors for complex traits, the choice and design of methods for statistical analysis in these populations deserve particular care. We show that methods designed for outbred samples are generally not appropriate for isolated populations and could lead to false conclusions.

Chromosome Mapping↗
PubMedDate not supplied

Recent research on immigrant health from statistics Canada's population surveys.

This paper reviews recent research using Statistics Canada data to compare immigrant health with that of the Canadian-born. A number of Statistics Canada studies have been used for such comparisons, including the National Population Health Survey and the Canadian Community Health Survey. Across the range of indicators studied, compared to the Canadian-born, immigrants are generally in as good or better health, have similar or better health behaviours, and similar or less frequent health service use (the "healthy immigrant effect"). These indications appear to be strongest among recent and non-European immigrants. These studies have established baseline patterns and identified that important distinctions exist among immigrant subgroups. Future research on more detailed subgroups that uses longitudinal data and cross-culturally validated instruments is needed.

Alcoholism↗
PubMed2004

Evaluation of methodologies for small area life expectancy estimation.

STUDY OBJECTIVE: To evaluate methods for calculating life expectancy in small areas, for example, English electoral wards. DESIGN: The Monte Carlo method was used to simulate the distribution of life expectancy (and its standard error) estimates for 10 alternative life table models. The models were combinations of Chiang or Silcocks methodology, 5 or 10 year age intervals, and a final age interval of 85+, 90+, or 95+. SETTING: A hypothetical small area experiencing the population age structure and age specific mortality rates of English men 1998-2000. PARTICIPANTS: Routine mortality and population statistics for England. MAIN RESULTS: Silcocks and Chiang based models gave similar estimates of life expectancy and its standard error. For all models, life expectancy was increasingly overestimated as the simulated population size decreased. The degree of overestimation depended largely on the final age interval chosen. Life expectancy estimates of small populations are normally distributed. The standard error estimates are normally distributed for large populations but become increasingly skewed as the population size decreases. Substitution methods to compensate for the effect of zero death counts on the standard error estimate did not improve the estimate. CONCLUSIONS: It is recommended that a population years at risk of 5000 is a reasonable point above which life expectancy calculations can be performed with reasonable confidence. Implications are discussed. Within the UK, the Chiang methodology and a five year life table to 85+ is recommended, with no adjustments to age specific death counts of zero.

Aged↗
PubMed1994

Statistical methods for estimating the effective number of alleles, expected heterozygosity and genetic distance in self-incompatibility locus.

In order to understand the evolutionary process of self-incompatibility, we must know the genetic variability of the self-incompatibility genes within and between populations. Statistical methods for estimating the effective number of alleles, expected heterozygosity and genetic distance from pollination experiments were developed, which can be applied to both gametophytic and sporophytic self-incompatibility systems. In these methods, bud-pollination, which is necessary for obtaining homozygotes, is not required. Since bud-pollination, which is time-consuming, is not required in the present methods, they might be useful.

Alleles↗
PubMed1986

The rate of convergence of a generalized stable population.

In an age-structured population that grows exponentially, each age group pi(t) at period t is asymptotically equivalent to x0t for some positive number x0. In this paper we show that the speed at which the ith age group reaches its exponential state of equilibrium can be measured by the rate at which the ratio vi(t) = pi(t)/pi(t-1) converges to x0. The age specific rate of convergence is determined by considering a quantity r satisfying [vi(t)-x0] less than or equal to rt when t is large; Ri = Inf r (over all initial populations, r satisfying the above inequality) is the R-factor used in numerical analysis to measure the rate at which the sequence vi(t) converges to x0; Si = -1n Ri is then defined as the rate of convergence to stability of the ith age group. The case of constant net maternity rates is studied in detail; in this context S0 is compared to the population entropy H, which was proposed by Tuljapurkar (1982) as a measure of the rate of convergence to stability.

Age Factors↗
PubMed2004

Population-based prediction of trauma volumes at a Level 1 trauma centre.

OBJECTIVE: With an ageing US population, the demographics of traumatic injuries are being significantly altered. Census projections predict that the number of Americans over age 65 will double in the next 20 years. We used stochastic methods to forecast trauma admissions in order to predict the effects of such demographic changes at our trauma centre. METHODS: Age- and sex-related rates of traumatic admission were determined using population statistics and trauma registry data from 1994 to 1999. These rates were then projected from 2000 to 2025 based on both the Lee-Carter and random walk with drift methods. Stochastic population projections were made and paired with the projected trauma rates, allowing estimation of total trauma volume. RESULTS: Trauma rates were predicted to increase for most age groups. Trauma admissions are predicted to increase 57% by 2024. By 2019, 50% of trauma admissions will be 60 or older. CONCLUSIONS: Our trauma volume is expected to increase 57% by 2024, an increase of 2% per year. More of this volume will consist of elderly patients, potentially requiring increased health-care resources.

Adolescent↗