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PubMed1996

The Impact of Environmental Variation on Demographic Convergence of Leslie Matrix Population Models: An Assessment Using Lyapunov Characteristic Exponents

In a constant environment, the rate of convergence of a density-independent Leslie matrix model to stable age distribution is determined by the damping ratio (the ratio of the absolute magnitudes of the first and second eigenvalues of the projection matrix). In a stochastic environment, the difference between the first two Lyapunov exponents is known to be analogous to the logarithm of the damping ratio, but there has been no systematic investigation of the consequences of enviromnental variation on convergence rates. In this study, the Lyapunov spectrum has been calculated for a wide variety of density-independent projection matrices subject to random variations in vital rates. This allows the impact of these random variations on convergence rates to be assessed. For rapidly convergent life histories, stochastic variation leads to a decrease in convergence rate. For life histories which are slow to converge, stochastic variation speeds up convergence. These effects are, however, relatively minor, and the value of the damping ratio for the mean matrix is a good predictor of the damping ratio in a stochastic environment. Consequently, when only an approximate indication of convergence rates is needed, the damping ratio for the mean projection matrix gives a very good guide. Detailed calculations of the Lyapunov spectrum would only be necessary to make comparisons between similar life histories or if very precise information on convergence rates were needed.

Journal Article↗
PubMed2003

The evolution of human phenotypic plasticity: age and nutritional status at maturity.

Several evolutionary optimal models of human plasticity in age and nutritional status at reproductive maturation are proposed and their dynamics examined. These models differ from previously published models because fertility is not assumed to be a function of body size or nutritional status. Further, the models are based on explicitly human demographic patterns, that is, model human life-tables, model human fertility tables, and, a nutrient flow-based model of maternal nutritional status. Infant survival (instead of fertility as in previous models) is assumed to be a function of maternal nutritional status. Two basic models are examined. In the first the cost of reproduction is assumed to be a constant proportion of total nutrient flow. In the second the cost of reproduction is constant for each birth. The constant proportion model predicts a negative slope of age and nutritional status at maturation. The constant cost per birth model predicts a positive slope of age and nutritional status at maturation. Either model can account for the secular decline in menarche observed over the last several centuries in Europe. A search of the growth literature failed to find definitive empirical documentation of human phenotypic plasticity in age and nutritional status at maturation. Most research strategies confound genetics with phenotypic plasticity. The one study that reports secular trends suggests a marginally insignificant, but positive slope. This view tends to support the constant cost per birth model.

Age Factors↗
PubMed1992

Age-dependent choice of sexual partners and the transmission dynamics of HIV in Sub-Saharan Africa.

A mathematical model of the transmission of HIV-1 within heterosexual populations in Sub-Saharan Africa is described and its properties analysed. The model incorporates epidemiological and demographic processes and extends previous work in this area via the inclusion of age and sex dependency in rates of sexual partner change, and sexual partner choice dependent on age. Parameter assignments are made on the basis of current data on the transmission dynamics of HIV-1 and the demography of human populations in Africa. Both age-dependent rates of sexual activity and the sexual contact of males with females younger than themselves act to enhance the predicted demographic impact. With realistic parameter values, the model suggests AIDS is able to reverse the sign of population growth rates from positive to negative values over a timescale of a few decades. The sensitivity of this prediction is examined in relation to changes in the pattern of sexual contact between different age classes of females and males, different patterns of change in the age-dependent rate of sexual partner change, different assumptions concerning the doubling time of the epidemic in its early stages, and the relative efficiencies of viral transmission between men and women, and vice versa. The impact AIDS is predicted to have on the number of young and elderly persons as a fraction of the number of productive adults (the dependancy ratio) is examined under various assumptions concerning the weighting to be applied to mirror the burden imposed by the care of those with AIDS. The paper includes an assessment of the influence of the timing of changes in sexual behaviour, or the promotion of the use of condoms, on the predicted course of the epidemic. The paper concludes with a discussion of data needs and the model refinements required to more accurately mirror current understanding of the epidemiology of HIV-1.

Acquired Immunodeficiency Syndrome↗
PubMed1999

Recent demographic and injury trends in people served by the Model Spinal Cord Injury Care Systems.

OBJECTIVE: To identify trends in the demographic and injury data of persons with spinal cord injury (SCI). DESIGN: Consecutive case series. SETTINGS: Model Spinal Cord Injury Care Systems throughout the United States. PATIENTS: A total of 25,054 persons admitted to a Model Spinal Cord Injury Care System within 365 days of injury between 1973 and 1998. RESULTS: Many trends and changes have been noted in the clinical features of patients who have been admitted to the Model SCI Care Systems. Average age at time of injury is rising; persons older than 60 comprise 11.5% of all persons enrolled in the National Database during the 1994-1998 period. Although the overall male-to-female ratio is greater than 4:1, the proportion of males has decreased significantly in recent years. Violence-related injuries have increased dramatically from 13.9% in 1973-1977 to 21.8% in 1994-1998. Since 1973, the proportions of injuries resulting from vehicular crashes and sports declined while injuries from falls increased. Injury continues to occur most commonly in the summer. When age, race, and gender are considered, violence is a more common cause of injury among individuals who are younger, male, or African American. Complete injuries were more common among younger individuals and among men than among older adults and women. CONCLUSION: Trends in the national database provide valuable data for tracking groups at risk for traumatic SCI.

Adolescent↗
PubMed1998

What predicts medical student career choice?

The literature on medical student career choice has identified several influences that can be categorized as student demographics, medical school characteristics, students' perceptions of specialty characteristics, and student-held values. A logistic regression model that included demographics, medical school, and student-rated influences as a proxy for perceptions and values was used to determine their relative contribution to student career choice for three consecutive cohorts of senior medical students attending two schools (n = 649). This model identified a positive relation between choice of primary care career and both student-rated influences and one student demographic characteristic, but not between career choice and school attended. Variables positively correlated with primary care career choice were related to working with people and marital status. Negatively correlated variables were related to income and prestige.

Adult↗
PubMed2000

Fluctuating Environments and Phytoplankton Community Structure: A Stochastic Model.

Spatial heterogeneity in organism and resource distributions can generate temporal heterogeneity in resource access for simple organisms like phytoplankton. The role of temporal heterogeneity as a structuring force for simple communities is investigated via models of phytoplankton with contrasting life histories competing for a single fluctuating resource. A stochastic model in which environmental and demographic stochasticity are treated separately is compared with a model with deterministic resource variation to assess the importance of stochasticity. When compared with the deterministic model, the stochastic model allows for coexistence over a wider range of parameter values (or life-history types). The model suggests that demographic stochasticity alone is far more important in increasing the possibility of coexistence than environmental stochasticity alone. However, the combined effects of both types of stochasticity produce the largest likelihood of coexistence. Finally, the influence of relative nutrient levels and nutrient pulse frequency on these results is addressed. We relate our findings to variable environment theory with evidence for both relative nonlinearity and the storage effect acting in this model. We show for the first time that temporal dynamics generated by demographic stochasticity may operate like the storage effect at particular spatial scales.

competition↗
PubMed2026

Discovery and validation of a multi-protein panel for predicting non-fatal major adverse cardiovascular events in diabetic kidney disease.

OBJECTIVE: To identify plasma protein biomarkers associated with incident non-fatal major adverse cardiovascular events (MACE) in diabetic kidney disease (DKD) patients. RESEARCH DESIGN AND METHODS: We analyzed 317 DKD patients from the UK Biobank. Plasma proteomics and clinical data (demographics, metabolism, renal function) were integrated. In an exploratory discovery phase, three sequential Cox regression models (crude, socio-demographic-adjusted, socio-demographic-metabolic adjusted) screened non-fatal MACE-associated proteins. To prevent information leakage, the cohort was then randomly split into training (70%) and testing (30%) sets; machine-learning feature selection, hyperparameter optimization, and final model development were performed exclusively within the training set. The associated proteins were input into the four-step machine-learning pipeline (LASSO-Cox, random survival forest, Boruta, XGBoost-Cox). Predictive performance was validated using Kaplan-Meier survival analyses, longitudinal trajectory modeling, and ROC benchmarking. An interactive web application was deployed for clinical implementation. RESULTS: Of 1,463 plasma proteins, 561 were associated with non-fatal MACE across Cox models, with 14 overlapping proteins. Nine core proteins (ANG, IL1R1, CXCL14, ESAM, PTGDS, HAVCR1, FGFR2, IGSF8, CCL3) were validated: ANG showed the strongest non-fatal MACE association (HR&#xa0;=&#xa0;3.88, 95%CI 2.33-6.48, p<0.001), and all high-expression groups had elevated non-fatal MACE risk. GO/KEGG enrichment highlighted inflammatory-immune pathways like positive regulation of MAPK cascade, Cytokine-cytokine receptor interaction and PI3K-Akt signaling pathway as key mechanisms. The model integrating proteins, demographic factors, and clinical variables achieved the highest predictive performance across non-fatal MACE (AUC&#xa0;=&#xa0;0.768), myocardial infarction (MI) (0.808), and stroke (0.816) outcomes, with superior stability in cross-validation. CoxBoost + Elastic Net framework was selected as the optimal framework via benchmarking of 101 algorithms. The model demonstrated favorable calibration in high-risk patients and yielded positive net clinical benefit across decision thresholds of 5% to 45%. The web tool (https://jiangli2941.github.io/MACE-prediction-v2/) enables input of 28 variables, outputs non-fatal MACE risk status, risk probability, and highlights abnormal indicators. CONCLUSION: Plasma proteomics combined with machine learning identifies robust non-fatal MACE predictors in DKD.

Humans↗
PubMed1996

Endogenous fertility and the Henry George Theorem.

"Models of endogenous demographic change deal with population size as an additional object of the welfare analysis. In these models the overlapping-generations (OLG) model serves as the basic framework. In club theory, too, population size is treated as an endogenous variable. In local public goods (LPG) models, the so-called Henry George Theorem, which requires local public expenditures to be financed by a 100% tax on aggregate land rent, is known as a (first-order) condition for club efficiency. The present paper establishes and exploits an isomorphism between steady states of the OLG model and allocations of the LPG model. The paper revisits Samuelson's fallacy concerning his goldenest golden rule and it explores institutional arrangements that sustain the optimum growth of population."

Demography↗
PubMed1996

Direct and indirect effects of demographic, medical, and psychological variables on neuropsychological performance in normal geriatric persons: a structural equation model.

The direct and indirect effects of demographic, medical, and psychological variables on neuropsychological performance in elderly individuals were examined using a LISREL structural equation model. One-hundred fifty-six geriatric subjects were individually administered a comprehensive neuropsychological battery, an extensive medical history and demographics questionnaire, and the Neuropsychology Behavior and Affect Profile (a psychological assessment instrument). The model assessed the effects of five independent latent variables (medical history, psychological functioning, global mental status, education, and gender-related functioning) on two dependent latent variables (nonverbal and verbal neuropsychological functioning). The best fitting model revealed that three latent variables (medical history, global mental status, and gender-related functioning) had direct effects on neuropsychological functioning and that all five independent variables exhibited indirect effects. These findings suggest that the influence of demographic variables on neuropsychological functioning for geriatric persons is complex and that certain variables should not be interpreted independently of each other due to their significant moderating influences.

Aged↗
PubMed1984

Econometrically accounting for identities and restrictions in models of interregional migration.

"Interregional demographic identities and other restrictions are explicitly taken into account in a simple time-series model of interregional migration. This goal is accomplished through the imposition of adding-up constraints on the estimated coefficients of a multi-equation linear system and by testing for homogeneity and symmetry. The pitfalls of utilizing the described procedures for migration analysis and forecasting are discussed. Full implementation of the technique is shown to require far more time-series observations on interregional migration than are commonly available."

Demography↗
PubMed2004

Modeling the metabolic effects of terbutaline in beta2-adrenergic receptor diplotypes.

OBJECTIVE: Our objective was to determine whether beta(2)-adrenergic receptor polymorphisms influence terbutaline-stimulated changes in glucose, insulin, and potassium concentrations in healthy adults. METHODS: Seven healthy adults homozygous for the Arg-19/Gly16/Glu27 haplotype (RGE) and seven homozygous for the Cys-19/Arg16/Gln27 haplotype (CRQ) volunteered to receive a 1-hour infusion of terbutaline (0.01 mg/kg). A 2-compartment pharmacokinetic model was fitted to the terbutaline concentrations. Concentrations of glucose and insulin were fitted simultaneously by use of a coupled feedback indirect response model. An indirect response model was also fitted to the plasma potassium concentration versus time data. The -2 log-likelihood ratio test was used to determine whether estimates of the covariates of diplotype and sex improved the model fittings. RESULTS: Demographic variables, anthropometric characteristics, and pharmacokinetics did not differ by diplotype. The coupled feedback model fitted the glucose and insulin concentration data well with excellent precision. Terbutaline stimulated production of glucose (S(1)) to a greater extent in RGE compared with CRQ diplotypes, as follows: S(1) = 0.039 +/- 0.007 (mean +/- SD) versus 0.0276 +/- 0.01, respectively (P <.05, -2 log-likelihood criterion). The baseline values, disposition rate constants for glucose (k(out1)) and insulin (k(out2)), production rate of insulin (S(2)), feedback effect of insulin on glucose (S(3)), and pharmacodynamic parameters for potassium did not differ by diplotype or sex. CONCLUSIONS: The beta(2) receptor diplotype influences receptor-stimulated glucose production in healthy, nonobese individuals, which is consistent with beta(2) receptor-mediated hepatic glycogenolysis. Future metabolic studies of this system should consider beta(2) receptor genetic variants.

Adolescent↗
PubMed2000

[Hospital mortality in subarachnoid hemorrhage. Experience of the "Barcelona Registry of Cerebrovascular Diseases"].

OBJECTIVES: To determine clinical predictors of in-hospital mortality in patients with non-traumatic subarachnoid hemorrhage. PATIENTS AND METHODS: Data de 184 patients with subarachnoid hemorrhage were obtained from consecutive stroke included in the prospective "Barcelona Stroke Registry". Demographic, anamnestic, clinical, neuroimaging and outcome variables in the subgroup of patients who died were compared with those in the surviving subgroup. The independent predictive value of each variable on the development of death was assessed with a logistic regression analysis. Three predictive models were constructed. A first model was based on demographic and clinical variables (total 10 variables). A second model was based on demographic, clinical and neuroimaging variables (total 17). A third model was based on demographic, clinical, neuroimaging and outcome variables (total 21). RESULTS: In-hospital death was observed in 44 patients (24%). Transient neurological deficit (OR = 13.92; 95% CI: 1.01-191.95), progressive deficit (OR = 4.21; 95% IC: 1.28-13.86), limb weakness (OR = 3.24; 95% IC: 1.49-7.08) and age (OR = 1.05; 95% CI: 1.02-1.09) appeared to be independent prognostic factors of in-hospital mortality in the first predictive model. In addition to these variables, intraventricular hemorrhage (OR = 5.51; 95% CI: 1.94-16.04) was selected in the second predictive model. Transient neurological deficit (OR = 41.2; 95% CI: 1.61-1056.2), neurological complications (OR = 11.04; CI del 95%: 3.85-31.74), carotid aneurysm (OR = 6.61; 95% CI: 1.23-35.43), intraventricular hemorrhage (OR = 5.51; 95% CI: 1.65-18.4), progressive deficit (OR = 5.35; 95% CI: 1.11-25.90) and hemispheric intracerebral hemorrhage (OR = 4.32; 95% CI: 1.35-13.90), appeared to be independent prognostic factors of in-hospital mortality in the third model. CONCLUSIONS: Clinical features easily obtained at the patient's bedside in addition to neuroimaging data easily obtained in routine neuroimaging studies help clinicians to predict in-hospital mortality in patients with subarachnoid hemorrhage. Transient neurological deficit prior to definitive subarachnoid hemorrhage was the main clinical predictor of in-hospital mortality.

Aged↗
PubMed2006

Incorporating movement into models of grey seal population dynamics.

1. One of the most difficult problems in developing spatially explicit models of population dynamics is the validation and parameterization of the movement process. We show how movement models derived from capture-recapture analysis can be improved by incorporating them into a spatially explicit metapopulation model that is fitted to a time series of abundance data. 2. We applied multisite capture-recapture analysis techniques to photo-identification data collected from female grey seals at the four main breeding colonies in the North Sea between 1999 and 2001. The best-fitting movement models were then incorporated into state-space metapopulation models that explicitly accounted for demographic and observational stochasticity. 3. These metapopulation models were fitted to a 20-year time series of pup production data for each colony using a Bayesian approach. The best-fitting model, based on the Akaike Information Criterion (AIC), had only a single movement parameter, whose confidence interval was 82% less than that obtained from the capture-recapture study, but there was some support for a model that included an effect of distance between colonies. 4. The state-space modelling provided improved estimates of other demographic parameters. 5. The incorporation of movement, and the way in which it was modelled, affected both local and regional dynamics. These differences were most evident as colonies approached their carrying capacities, suggesting that our ability to discriminate between models should improve as the length of the grey seal time series increases.

Animal Migration↗