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At least 127 records · Page 7Linked to original sources
PubMed1988

A generalized stable model with fluctuating vital rates.

The amenability of the stable population model to certain situations where net maternity function need not be invariant over time is exemplified by relating the changes in fertility at 2 time points by the equation m(a,t) = m(a) h(a,t)/h(t) where the form of h(t) is general and can be determined based on observed birth trajectories. Using the extended form of Easterlin's hypothesis, h(t) is taken as the reciprocal of NRR at t. The model is then applied to project NRR.

Birth Rate↗
PubMed1991

[On measuring instability in demography].

"A concept of instability as an integral measure for estimating [the] age structure of real and stable populations is substantiated. A system of instability indices is suggested [that] permits estimating the effect of external conditions and internal factors of population reproduction on the age structure." The geographical focus is on the USSR. (SUMMARY IN ENG)

Age Distribution↗
PubMed1974

Linkage disequilibrium in natural populations of Drosophila melanogaster.

Two large, stable populations (Texas and Japan) of Drosophila melanogaster were surveyed at 21 allozyme loci on the second and third chromosomes and for chromosomal gene arrangements on those two chromosomes. Over 220 independent gametes were sampled from each population. The types and frequencies of the surveyed genetic variation are similar to those observed previously and suggest only slight differentiation among geographically distant populations. Linkage disequilibrium among linked allozymes loci is only slightly, if at all, detectable with these sample sizes. Linkage disequilibrium between linked inversions and allozymes loci is common especially when located in the same arm. These disequilibria appear to be in the same direction for most comparisons in the two population samples. This result is interpreted as evidence of similar selective environments (ecological and genetic) in the two populations. It is also noted that the direction of these linkage disequilibria appears to be oriented with respect to the gene frequencies at the component loci.

Alcohol Oxidoreductases↗
PubMed2006

Age-structured homogeneous epidemic systems with application to the MSEIR epidemic model.

In this paper, we develop a new approach to deal with asymptotic behavior of the age-structured homogeneous epidemic systems and discuss its application to the MSEIR epidemic model. For the homogeneous system, there is no attracting nontrivial equilibrium, instead we have to examine existence and stability of persistent solutions. Assuming that the host population dynamics can be described by the stable population model, we rewrite the basic system into the system of ratio age distribution, which is the age profile divided by the stable age profile. If the host population has the stable age profile, the ratio age distribution system is reduced to the normalized system. Then we prove the stability principle that the local stability or instability of steady states of the normalized system implies that of the corresponding persistent solutions of the original homogeneous system. In the latter half of this paper, we prove the threshold and stability results for the normalized system of the age-structured MSEIR epidemic model.

Age Factors↗
PubMed2000

Multiple oscillators provide metastability in rhythm generation.

Biological rhythms such as cardiac and circadian rhythms arise from activity of multiple oscillators with dispersed intrinsic frequencies. It has been proposed that a stable population rhythm, fundamental to normal physiological processes, can be achieved in these systems by synchronization, through mutual entrainment, of individual oscillators. Mutual entrainment, however, is unlikely to be the mechanism underlying the generation of a stable rhythm in a population of multiple weakly coupled or uncoupled oscillators. We have recently identified such a population that is involved in the sympathetic regulation of vascular tone in a thermoregulatory circulation. In this paper, we investigate the stability of the output rhythm of these sympathetic oscillators by subjecting the system to a periodic driving force (the lung inflation cycle-related activity). We show that a population rhythm coupled to the drive can remain stable over a much wider driving frequency range compared with that of any one of its constituent oscillators. This population rhythmicity still exists despite the fact that the dominant frequencies of individual oscillators are not necessarily 1:1 frequency-locked to the drive. We provide evidence to show that this population metastability is achieved through linear and nonlinear dynamic interactions between the driving force and single sympathetic oscillators. Our study suggests that the generation of a stable population rhythm can exist even in the absence of mutual entrainment of its constituents, and this allows the population to generate a stable and flexible patterned response.

Activity Cycles↗
PubMed1992

[[A dynamic model for populations reproduced by first marriage]].

Using data for Japan, the author analyzes "the effect of nuptiality and of marital fertility [on population trends and constructs] a population model in which childbearing occurs only within first marriage....First, we can prove that...we can construct a stable population theory based on nuptiality and marital fertility....Next..., we investigate the effect of [the age shift in first marriage patterns on total fertility rates], since delay of marriage has been thought to be one of [the] major causes for long-term fertility decline in Japan. We conclude that although [the age shift in first marriage patterns] could decrease Japanese fertility, its effect seems to be insufficient to induce such rapid fertility decline as is observed recently in Japan." (SUMMARY IN ENG)

Age Factors↗
PubMed1993

Trends in hospitalization for heart failure in Scotland 1980-1990.

Heart failure is a growing public health problem in industrialized countries with ageing populations. Scotland has a relatively stable population of approximately 5 million and a well described system for recording details of hospitalizations (Scottish Hospital In-Patients Statistics-SHIPS). We have examined SHIPS data for hospitalizations for heart failure in Scotland 1980-1990. Discharges for heart failure as the primary diagnosis increased by almost 60%, from 1.30 to 2.12/1000 population in this period (as either primary or secondary diagnosis the rate increased from 2.51 to 4.24/1000). Seventy-eight percent of discharges were in persons aged > or = 65 years and 48% of discharges were male. Heart failure (primary diagnosis) accounted for almost 4% of all general (internal) medicine discharges. In-patient case fatality was 18% in 1990. Mean duration of in-patient stay on Internal Medicine wards was approximately 11 days. The number of hospitalizations for heart failure is now almost identical to those for myocardial infarction. These trends mirror those recently reported from the United States. Heart failure is an increasingly common and costly cause of hospitalization in Scotland. Approaches which can reduce this burden on the hospital service require urgent attention.

Adult↗
PubMed1997

Type I autoimmune hepatitis is primarily a disease of later life.

Previous studies of type I autoimmune hepatitis (AIH) have been based on selected populations attending specialist liver units. We describe 41 patients with type I AIH from a stable population in South Wales sequentially diagnosed over an 11-year period. All were Caucasian; 32 women, nine men; median follow-up 4 years. All cases conformed with International AIH Group criteria. Median age at diagnosis was 62 years. At presentation, only five patients were under 40 years old, 23 were over 60. This was very different from the classical age distribution. The commonest presentation was acute icteric hepatitis (29/41); median duration of illness 3 months. Co-existing acute arthralgia was common (10/41), as were other autoimmune diseases. Liver biopsy revealed piecemeal necrosis or interface hepatitis in 30; others showed non-diagnostic acute hepatitis. Fourteen also had cirrhosis. Median AsT fell from 508 (73-2385) to 32 (13-607) U/I after immunosuppression, representing complete remission in 28, partial remission in eight, and two treatment failures. Three patients were not treated, because of either quiescent disease or spontaneous remission. To date, there have been eight deaths (median age 64, range 37-86); five due to liver failure, one to variceal haemorrhage, one to acute myocardial infarction and one to upper gastrointestinal haemorrhage caused by acute idiopathic thrombocytopenia. Contrary to previous descriptions, type 1 AIH is a disease of later life in this stable, unselected population; peak incidence was in the seventh decade, and few cases occurred before the fifth decade. Presentation was usually as painless acute icteric hepatitis. Immunosuppression was effective and safe in most cases; 5-year survival rates were 61% (> 60 years at diagnosis), 66% (< 60) and 64% (overall).

Adolescent↗
PubMed1996

Stabilization, birth waves, and the surge in the elderly.

This study examines the transition of a population to stability following a shift to a new fixed set of vital rates. Specifically, the authors develop a simple discrete population model and use it to derive an explicit solution for the birth trajectory. "The new vital rates interact with the population's initial age composition and generate birth waves whose amplitude and attenuation depend on the ratio of ultimate to initial growth and on the new pattern of stable net maternity. A greater change in growth and a later stable net maternity pattern produce larger fluctuations in the number of births. Stabilization begins at the youngest ages and proceeds upward. Sixty years after the shift, the birth waves have largely disappeared and the proportion under age 15 approximates the stable level implied by the new rates. Those patterns are manifest in the stabilization of both observed and Coale-Demeny model stable populations." (SUMMARY IN FRE)

Age Distribution↗
PubMed1992

Optimal estimate of population age structure with varying vital rates.

The author presents a method for estimating the age distribution of a population under varying vital statistics. "Some mathematical aspects of the method, as well as its applicability, will be discussed and numerical simulation will be run to illustrate the results and to compare the method with the traditional estimate of stable population theory...."

Age Distribution↗
PubMed1993

Cancer incidence in Turin: the effect of migration.

AIMS AND BACKGROUND: Studies on migrant populations have been of great value in clarifying the role of environmental factors in cancer occurrence. Most of them consider migrants from other countries or continents. Turin, the target territory of this study, was an important area of internal migration initially from the East, and more recently from southern Italy. METHODS: The study compared incidence rates (age-standardized) of the native population, of the migrants and incidence rates of the Cancer Registries located in the four main areas of origin. RESULTS: Overall incidence rates in migrants from southern Italy were intermediate compared with those of the stable populations of the South and the North. The same effect was not true for people from the North-East, who migrated in earlier decades. In this population, migration towards lower-incidence areas did not reduce cancer incidence. Migrants from the South showed a significant increase in intestinal, breast, and tobacco-related tumors compared to the stable southern population. No effect of migration was found for cancer of the mouth, pharynx, esophagus, stomach or corpus uteri. Incidence of liver cancer in migrant southern males was significantly different from the stable and the native north-western population. CONCLUSIONS: The results, based on incidence data, validated previous findings based on mortality data on the effect of Italian internal migrations and showed that migrants underwent changes in some environmental exposures. In particular, migrants from the South to the North of Italy came into contact with new risk factors, with an increase in occurrence of cancer.

Female↗
PubMed1985

The dynamics of urban population.

The relative roles of natural increase and migration in determining the long-term dynamics of an urban population are considered. "Rogers' model is used to represent the simultaneous growth of a multiregional population. Exploiting the mathematical structure of the resulting system of difference equations, a perturbation theory for demographic models [is] outlined. This theory provides useful tools for analysing the sensitivity of stable population distribution and rate of growth to changes in the fundamental demographic parameters. With respect to the conventional approach to sensitivity analysis, it does not require the sometimes cumbersome calculation of matrix derivatives." A numerical example is given to demonstrate the method. (SUMMARY IN FRE AND ITA)

Demography↗
PubMed1985

Population Dynamics of Soil Pseudomonads in the Rhizosphere of Potato (Solanum tuberosum L.).

Rhizosphere population dynamics of seven Pseudomonas fluorescens and Pseudomonas putida strains isolated from rhizospheres of various agricultural plants were studied on potato (Solanum tuberosum L.) in field soil under controlled environmental conditions. Rhizosphere populations of two strains (B10 and B4) were quantitatively related to initial seed piece inoculum levels when plants were grown at -0.3 bar matric potential. At a given inoculum level, rhizosphere populations of strain B4 were consistently greater than those of strain B10. In vivo growth curves on 4-cm root tip-proximal segments indicated that both strains grew at similar rates in the potato rhizosphere, but large populations of strain B10 were not maintained at 24 degrees C after 7 h, whereas those of strain B4 were maintained for at least 40 h. Although both strains grew more rapidly in the rhizosphere at 24 degrees C than at 12 degrees C, their rhizosphere populations after seed piece inoculation were generally greater at 12 or 18 degrees C, indicating that in vivo growth did not solely determine rhizosphere populations in these studies. In vitro osmotolerance of seven Pseudomonas strains (including strains B4 and B10) was correlated with their abilities to establish stable populations in the rhizosphere of potato. Stability of rhizosphere populations of the Pseudomonas strains studied here was maximized at low (i.e., 12 degrees C) soil temperatures. These results indicate that Pseudomonas strains differ in their capacity to maintain stable rhizosphere populations in association with potato. This capacity, distinct from the ability to grow in the rhizosphere, may limit the establishment of rhizosphere populations under some environmental conditions.

Journal Article↗
PubMed2000

Prospects for phase III-IV HPV vaccination trials in the Nordic countries and in Estonia.

BACKGROUND: oncogenic, i.e. high risk human papillomavirus (hrHPV) types are the major cause of invasive cervical cancer (ICC). Putatively licensable vaccines against the hrHPVs have been developed and are approaching clinical phase III trials that use persistent HPV infection as end point. Direct extension of the phase III trials towards long-term end points (ICC and its immediate precursors: carcinoma in situ and severe dysplasia, i.e. cervical intraepithelial neoplasia grade III, CINIII) is important, to avoid early contamination of the target population by opportunistic use of licensed HPV vaccines. Country-wide registration on population and health events in a stable population of 25 million make Estonia and the Nordic countries a unique venue for long-term evaluation of cervical cancer control measures. Mass-screening programmes exist in all Nordic countries, but not in Estonia. AIM: design of phase III-IV trials for evaluation of protection against ICC and CINIII by preventive HPV vaccines based on cancer registry follow-up. RESULTS: in the Nordic countries, population based randomisation of all 15-year-old women to the vaccination (vaccine and placebo) and reference cohorts entering conventional Pap-smear screening after a clinical phase III trial would assure comparability of the cohorts. Enrollment of 10094 vaccinees +10094 placebo vaccinees +30282 other hrHPV negative women without vaccination at the age of 16 would give 80% power for the demonstration of 70% vaccine efficacy (VE) against ICC in 20 years by cancer registry follow-up. On the other hand, vaccination of 8303 Estonian hrHPV negative women among the entire 15-year-old female birth cohort (about 10000 women) with an already licensed HPV vaccine would enable demonstration of 70% VE against ICC by 20 years of registry follow-up of these and comparable 16606 women identified among the 16-19-year-old birth cohorts. CONCLUSIONS: evaluation of the protective effect of an HPV vaccine against ICC is possible both in countries with or without mass-screening. The effects of vaccination on spread of different HPVs in the population would need to be monitored, especially in Estonia. Ethical aspects, cost-benefit evaluation and comparisons with other new means of cervical cancer control warrant further investigation.

Adolescent↗
PubMed2004

Modelling non-additive and nonlinear signals from climatic noise in ecological time series: Soay sheep as an example.

Understanding how climate can interact with other factors in determining patterns of species abundance is a persistent challenge in ecology. Recent research has suggested that the dynamics exhibited by some populations may be a non-additive function of climate, with climate affecting population growth more strongly at high density than at low density. However, we lack methodologies to adequately explain patterns in population growth generated as a result of interactions between intrinsic factors and extrinsic climatic variation in non-linear systems. We present a novel method (the Functional Coefficient Threshold Auto-Regressive (FCTAR) method) that can identify interacting influences of climate and density on population dynamics from time-series data. We demonstrate its use on count data on the size of the Soay sheep population, which is known to exhibit dynamics generated by nonlinear and non-additive interactions between density and climate, living on Hirta in the St Kilda archipelago. The FCTAR method suggests that climate fluctuations can drive the Soay sheep population between different dynamical regimes--from stable population size through limit cycles and non-periodic fluctuations.

Animals↗
PubMed1994

Generalized Lotka distribution incorporating migration.

"This paper proposes to introduce the migration component into the stable population model and examine the stability of the age distribution. The analysis [is restricted] to one sex as [has been] done by others." The model is applied to Canadian data.

Age Distribution↗
PubMed2004

The incidence of adenocarcinoma in Barrett's esophagus in an institutionalized population.

OBJECTIVE: To ascertain the incidence rate of adenocarcinoma in Barrett's esophagus (ACE) in a stable population of 28,000 institutionalized intellectually disabled individuals (IDI) in whom the prevalence rate of Barrett's esophagus (BE) was previously estimated in a representative sample by 24 h pH monitoring and endoscopy, and in which all cases of ACE were ascertained over a 6-year period. These IDI do not smoke or drink alcohol and are known to have exceptionally high prevalence rates of gastro-esophageal reflux disease, and consequently of BE. METHODS: A population comprising 52,038 person-years was observed and all cases of ACE were ascertained. On the basis of the representative sample, the percentage of this population with BE was estimated to be 10.8%. ACE incidence rates could then be estimated and compared with those found in a free-living BE cohort after correction for age and gender differences. RESULTS: In IDI an incidence rate of ACE of 2.5/1000 person-years was found against 6.3/1000 person-years in the free-living BE cohort. However, the age distributions of the IDI and of the free-living BE cohort were very different, and after correction for this factor there was no significantly lower incidence rate of ACE in the IDI (relative risk, 0.79; P = 0.61). CONCLUSIONS: This is the first reported incidence study of ACE in a stable, well-defined population. In contrast to squamous cell carcinoma, our findings suggest only a minor role for smoking and alcohol in the etiology of ACE.

Adenocarcinoma↗