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Model Combining (model + combining)
Selected AbstractsA closer look at the relationship between life expectancy and economic growthINTERNATIONAL JOURNAL OF ECONOMIC THEORY, Issue 2 2009Théophile T. Azomahou O41; I20; J10 We first provide a nonparametric inference of the relationship between life expectancy and economic growth using historical data for 18 countries over the period 1820,2005. The obtained shape indicates convexity for low enough values of life expectancy and concavity for large enough values. We then study this relationship using a benchmark model combining "perpetual youth" and learning-by-investing. The generated relationship between life expectancy and economic growth is shown to be strictly increasing and concave. We finally examine two models departing from "perpetual youth" by assuming successively age-dependent earnings and age-dependent survival probabilities. With age-dependent earnings, the obtained relationship is hump-shaped, whereas age-dependent survival laws reproduce the convex,concave shape detected in prior empirical study. [source] Raptor predation and population limitation in red grouseJOURNAL OF ANIMAL ECOLOGY, Issue 3 2000Simon J. Thirgood Summary 1.,We assessed the impact of predation by hen harriers and peregrine falcons on a red grouse population in southern Scotland during 1992,98. Grouse density in April, July and October declined during this time, coincident with an increase in the numbers of breeding harriers and peregrines. 2.,Winter losses of grouse between October and April averaged 33% and were density-dependent. Raptors were the cause of about 70% of winter mortality and they killed about 30% of the grouse present in October. We were unable to determine whether winter mortality in raptors was additive to other losses. 3.,Summer losses of adult grouse between April and July averaged 30% and were density-dependent. Raptors were the cause of more than 90% of the early summer mortality of adult grouse. Summer losses of grouse chicks between May and July averaged 45% and were not density-dependent. Harriers killed about 28% of grouse chicks by late July and about 37% by the end of August. Summer raptor predation on adult grouse and chicks appeared to be largely additive to other losses and we estimated that it reduced autumn grouse densities by about 50%. 4.,A model combining the estimated reduction in autumn grouse density caused by raptors with the observed density dependence in winter loss predicted that, in the absence of raptors for 2 years, grouse density in spring would be 1·9 times greater, and grouse density in autumn 3·9 times greater, than in the presence of raptors. The model suggested that raptor predation prevented the grouse population from increasing and was thus a limiting factor. [source] FISH, FISHERS, SEALS AND TOURISTS: ECONOMIC CONSEQUENCES OF CREATING A MARINE RESERVE IN A MULTI-SPECIES, MULTI-ACTIVITY CONTEXTNATURAL RESOURCE MODELING, Issue 4 2002JEAN BONCOEUR ABSTRACT. This paper investigates some economic consequences of creating a marine reserve on both fishing and ecotourism, when the range of controllability of fishing effort is limited and the impact of the reserve on ecosystem is considered. The issue is illustrated by the example of creating a no-take zone in part of a region where fishing is managed through a limited entry license system, and which is inhabited by two interacting stocks: a stock of prey (fish) and a stock of predators (seals). While the former is targeted by commercial fishing, the latter is not subject to harvest but is a potential basis for a commercial non-extractive activity (seal watching). Analysis is conducted with the help of a bioeconomic model combining the features of marine reserve modeling and of multispecies modeling. Following a description of the model, results of several simulation runs are presented. These show that creating a marine reserve has more complex economic implications than predicted in studies focused exclusively on one stock and/or commercial fisheries. More specifically, the model shows that the dynamics of the two interacting stocks reduces the benefits of the no-take zone for the fishing industry, while it makes the creation of this zone provide an opportunity for the development of ecotourism. Due to this dynamics, the model suggests that the optimal size of the reserve is larger when ecotourism is taken into account along with fishing activities. [source] Optimal Design of VSI ,X Control Charts for Monitoring Correlated SamplesQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 8 2005Yan-Kwang Chen Abstract This paper develops an economic design of variable sampling interval (VSI),X control charts in which the next sample is taken sooner than usual if there is an indication that the process is off-target. When designing VSI,X control charts, the underlying assumption is that the measurements within a sample are independent. However, there are many practical situations that violate this hypothesis. Accordingly, a cost model combining the multivariate normal distribution model given by Yang and Hancock with Bai and Lee's cost model is proposed to develop the design of VSI charts for correlated data. An evolutionary search method to find the optimal design parameters for this model is presented. Also, we compare VSI and traditional ,X charts with respect to expected cost per unit time, utilizing hypothetical cost and process parameters as well as various correlation coefficients. The results indicate that VSI control charts outperform the traditional control charts for larger mean shift when correlation is present. In addition, there is a difference between the design parameters of VSI charts when correlation is present or absent. Copyright © 2005 John Wiley & Sons, Ltd. [source] Simultaneous use of serum IgG and IgM for risk scoring of suspected early Lyme borreliosis: graphical and bivariate analysesAPMIS, Issue 4 2010RAM B. DESSAU Dessau RB, Ejlertsen T, Hilden J. Simultaneous use of serum IgG and IgM for risk scoring of suspected early Lyme borreliosis: graphical and bivariate analyses. APMIS 2010; 118: 313,23. The laboratory diagnosis of early disseminated Lyme borreliosis (LB) rests on IgM and IgG antibodies in serum. The purpose of this study was to refine the statistical interpretation of IgM and IgG by combining the diagnostic evidence provided by the two immunoglobulins and exploiting the whole range of the quantitative variation in test values. ELISA assays based on purified flagella antigen were performed on sera from 815 healthy Danish blood donors as negative controls and 117 consecutive patients with confirmed neuroborreliosis (NB). A logistic regression model combining the standardized units of the IgM and IgG ELISA assays was constructed and the resulting disease risks graphically evaluated by receiver operating characteristic and ,predictiveness' curves. The combined model improves the discrimination between NB patients and blood donors. Hence, it is possible to report a predicted risk of disease graded for each individual patient, as is theoretically preferable. The predictiveness curve, when adapted to the local pretest probability of LB, allows high-risk and low-risk thresholds to be defined instead of cut-offs based on the laboratory characteristics only, and it allows the extent of under- and over-treatment to be assessed. It is shown that an example patient with low ELISA results in IgM and IgG, considered negative by the conventional cut-off, has a relatively high risk of belonging to the truly diseased population and a low risk of being false positive. Using a 20% high-risk threshold for advising the clinician to consider treatment, the sensitivity of the assay is increased from 76% to 85%, while the specificity is maintained at around 95%. [source] Hybrid Simulation Combining a High Fidelity Scenario with a Pelvic Ultrasound Task Trainer Enhances the Training and Evaluation of Endovaginal Ultrasound SkillsACADEMIC EMERGENCY MEDICINE, Issue 5 2009Daniel V. Girzadas Jr MD Abstract Objectives:, In this study, an endovaginal ultrasound (US) task trainer was combined with a high-fidelity US mannequin to create a hybrid simulation model. In a scenario depicting a patient with ectopic pregnancy and hemorrhagic shock, this model was compared with a standard high-fidelity simulation during training sessions with emergency medicine (EM) residents. The authors hypothesized that use of the hybrid model would increase both the residents' self-reported educational experience and the faculty's self-reported ability to evaluate the residents' skills. Methods:, A total of 45 EM residents at two institutions were randomized into two groups. Each group was assigned to one of two formats involving an ectopic pregnancy scenario. One format incorporated the new hybrid model, in which residents had to manipulate an endovaginal US probe in a task trainer; the other used the standard high-fidelity simulation mannequin together with static photo images. After finishing the scenario, residents self-rated their overall learning experience and how well the scenario evaluated their ability to interpret endovaginal US images. Faculty members reviewed video recordings of the other institution's residents and rated their own ability to evaluate residents' skills in interpreting endovaginal US images and diagnosing and managing the case scenario. Visual analog scales (VAS) were used for the self-ratings. Results:, Compared to the residents assigned to the standard simulation scenario, residents assigned to the hybrid model reported an increase in their overall educational experience (, VAS = 10, 95% confidence interval [CI] = 4 to 18) and felt the hybrid model was a better measure of their ability to interpret endovaginal US images (, VAS = 17, 95% CI = 7 to 28). Faculty members found the hybrid model to be better than the standard simulation for evaluating residents' skills in interpreting endovaginal US images (, VAS = 13, 95% CI = 6 to 20) and diagnosing and managing the case (, VAS = 10, 95% CI = 2 to 18). Time to reach a diagnosis was similar in both groups (p = 0.053). Conclusions:, Use of a hybrid simulation model combining a high-fidelity simulation with an endovaginal US task trainer improved residents' educational experience and improved faculty's ability to evaluate residents' endovaginal US and clinical skills. This novel hybrid tool should be considered for future education and evaluation of EM residents. [source] The prognostic value of ultrasound abnormalities and biological parameters in blood of fetuses infected with cytomegalovirusBJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 7 2008G Benoist Objective, To evaluate the prognostic value of ultrasound abnormalities and of selected biological parameters in blood of fetuses infected with cytomegalovirus (CMV). Design, Retrospective observational study. Setting, Two fetal medicine units in Paris, France. Population, All fetuses infected with CMV referred between 1998 and 2006. Methods, We retrospectively analysed data collected prospectively in 73 fetuses infected by CMV with a positive CMV polymerase chain reaction in amniotic fluid. Fetal blood sampling (FBS) was performed for evaluation of platelet count, plasma levels of aminotransferases and gamma-glutamyl transpeptidases (GGT), presence of viraemia and specific fetal immunoglobulin M. Targeted ultrasound examination was performed every fortnight. Ultrasound findings were categorised into normal examination and any ultrasound abnormality, which was further grouped as ultrasound abnormality of the fetal brain and noncerebral ultrasound abnormality. Main outcome measures, A combination of histological findings after termination of pregnancy and evidence of cytomegalic inclusion disease at birth when pregnancies were continued. Clinical symptoms at birth or histological lesions attributable to CMV were considered as poor outcome. Statistical analysis was conducted to determine the value of each parameter to predict outcome. Logistic regression was used to build up a multivariate model combining the relevant parameters. Results, In univariate analysis, only thrombocytopenia and the presence of any ultrasound abnormality were associated with a poor outcome (P < 10,4 for both abnormalities). In the multivariate analysis, both thrombocytopenia and the presence of ultrasound abnormalities remained significant independent predictors of a poor outcome. Based on univariate logistic regression, odds ratio for a poor outcome were 1.24, 7.2, 22.5 and 25.5 for each 10 000/mm3 decrease in platelet count, the presence of noncerebral, any ultrasound and cerebral ultrasound abnormalities, respectively. Conclusions, The prognosis of CMV-infected fetuses relies independently on both targeted ultrasound examination and fetal platelet count. FBS for platelet count may therefore justify FBS in infected fetuses even in the absence of ultrasound. features of brain involvement. [source] Mathematical analysis of the cone ERG photopic hill: Clinical applicationsACTA OPHTHALMOLOGICA, Issue 2007P LACHAPELLE Purpose: With brighter stimuli, the photopic ERG b-wave increases to a maximal value and then decreases to a plateau, a feature known as the Photopic Hill (PH). Recently, a mathematical model combining a Gaussian (GF) and a Logistic Growth (LGF) functions was developed to fit the PH (Hamilton et al., Vision Research, in press). We examined if this equation could help us sort out selected retinopathies. Methods: We compared PHs (background: 30 cd.m-2; intensities: -0.8 to 2.84 log cd.sec.m-2) obtained from normals (N=40) and patients (N=20) affected with Congenital Stationary Night Blindness (CSNB), Congenital Postreceptoral Cone Pathway Anomaly (CPCPA) and Retinitis Pigmentosa (RP) with the GL ratio [GL= Gb / (Gb+Vbmax)] were Gb and Vbmax represent the amplitude of the Gaussian and logistic (Vbmax) functions respectively. Results: The normal GL ratio is 0.60 ± 0.08 (mean ± 1SD) compared to ,1.0 in CSNB (almost pure GF) and 0.32±0.08 in CPCP [reduced GF (p<.05) and normal LF (p>.05)] patients. Six of the 8 RP patients had a GL ratio above 0.5 (mean GL= 0.70 ± 0.19) and 2 below (0.28 and 0.41). Of interest, while in some retinopathies, a decline in Gb and Vbmax occurred with disease progression (longitudinal and transversal comparisons), it did not always modify the GL ratio. Conclusions: Human PH can be dissected into two distinct and concomitant phenomena each represented by its own equation. Altghough the retinal origin of the GF and LGF awaits to be confirmed, use of this mathematical approach appears to add valuable information that will further refine the diagnosis of retinal disorders affecting the photopic (cone) pathway. Supported by CIHR and Réseau Vision. [source] | |||||||||||||