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Bayesian Modelling (bayesian + modelling)
Selected AbstractsHIERARCHICAL BAYESIAN MODELLING OF SOCIAL VARIATION IN THE AGE DEPENDENCE OF DISABILITY PREVALENCEAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 4 2005Patrick Graham Summary Motivated by a study of social variation in the relationship of functional limitation prevalence to age, this paper examines methods for modelling social variation in health outcomes. It is argued that, from a Bayesian perspective, modelling the dependence of functional limitation prevalence on age separately for each social group, corresponds to an implausible prior model, in addition to leading to imprecise estimates for some groups. The alternative strategy of fitting a single model, perhaps including some age-by-group interactions but omitting higher-order interactions, requires a strong prior commitment to the absence of such effects. Hierarchical Bayesian modelling is proposed as a compromise between these two analytical approaches. Under all hierarchical Bayes analyses there is strong evidence for an ethnic group difference in limitation prevalence in early- to mid-adulthood among tertiary-qualified males. In contrast, the single-model approach largely misses this effect, while the group-specific analyses exhibit an unrealistically large degree of heterogeneity in gender-education-specific ethnicity effects. The sensitivity of posterior inferences to prior specifications is studied. [source] Zinc and nitrate in the ground water and the incidence of Type 1 diabetes in FinlandDIABETIC MEDICINE, Issue 3 2004E. Moltchanova Abstract Aims In Finland, the risk of childhood Type 1 diabetes varies geographically. Therefore we investigated the association between spatial variation of Type 1 diabetes and its putative environmental risk factors, zinc and nitrates. Methods The association was evaluated using Bayesian modelling and the geo-referenced data on diabetes cases and population. Results Neither zinc nor nitrate nor the urban/rural status of the area had a significant effect on the variation in incidence of childhood Type 1 diabetes. Conclusions The results showed that although there was no significant difference in incidence between rural and urban areas, there was a tendency to increasing risk of Type 1 diabetes with the increasing concentration of NO3 in drinking water. The fact that no significant effect was found may stem from the aggregated data being too crude to detect it. [source] Estimating the snow water equivalent on the Gatineau catchment using hierarchical Bayesian modellingHYDROLOGICAL PROCESSES, Issue 4 2006Ousmane Seidou Abstract One of the most important parameters for spring runoff forecasting is the snow water equivalent on the watershed, often estimated by kriging using in situ measurements, and in some cases by remote sensing. It is known that kriging techniques provide little information on uncertainty, aside from the kriging variance. In this paper, two approaches using Bayesian hierarchical modelling are compared with ordinary kriging; Bayesian hierarchical modelling is a flexible and general statistical approach that uses observations and prior knowledge to make inferences on both unobserved data (snow water equivalent on the watershed where there is no measurements) and on the parameters (influence of the covariables, spatial interactions between the values of the process at various sites). The first approach models snow water equivalent as a Gaussian spatial process, for which the mean varies in space, and the other uses the theory of Markov random fields. Although kriging and the Bayesian models give similar point estimates, the latter provide more information on the distribution of the snow water equivalent. Furthermore, kriging may considerably underestimate interpolation error. Copyright © 2006 Environment Canada. Published by John Wiley & Sons, Ltd. [source] Hierarchical Bayesian modelling of wind and sea surface temperature from the Portuguese coastINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2010Ricardo T. Lemos Abstract In this work, we revisit a recent analysis that pointed to an overall relaxation of the Portuguese coastal upwelling system, between 1941 and 2000, and apply more elaborate statistical techniques to assess that evidence. Our goal is to fit a model for environmental variables that accommodate seasonal cycles, long-term trends, short-term fluctuations with some degree of autocorrelation, and cross-correlations between measuring sites and variables. Reference cell coding is used to investigate similarities in behaviour among sites. Parameter estimation is performed in a single modelling step, thereby producing more reliable credibility intervals than previous studies. This is of special importance in the assessment of trend significance. We employ a Bayesian approach with a purposely developed Markov chain Monte Carlo method to explore the posterior distribution of the parameters. Our results substantiate most previous findings and provide new insight on the relationship between wind and sea surface temperature off the Portuguese coast. Copyright © 2009 Royal Meteorological Society [source] Revised age estimate of the Mjáuvøtn tephra A on the Faroe Islands based on Bayesian modelling of 14C dates from two lake sequences,JOURNAL OF QUATERNARY SCIENCE, Issue 5 2010Jesper Olsen Abstract Tephra horizons are potentially perfect time markers for dating and cross-correlation among diverse Holocene palaeoenvironmental records such as ice cores and marine and terrestrial sequences, but we need to trust their age. Here we present a new age estimate of the Holocene Mjáuvøtn tephra A using accelerator mass spectrometry 14C dates from two lakes on the Faroe Islands. With Bayesian age modelling it is dated to 6668,6533,cal. a BP (68.2% confidence interval) , significantly older and better constrained than the previous age. Copyright © 2010 John Wiley & Sons, Ltd. [source] Bayesian modelling of catch in a north-west Atlantic fisheryJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 3 2002Carmen Fernández Summary. We model daily catches of fishing boats in the Grand Bank fishing grounds. We use data on catches per species for a number of vessels collected by the European Union in the context of the Northwest Atlantic Fisheries Organization. Many variables can be thought to influence the amount caught: a number of ship characteristics (such as the size of the ship, the fishing technique used and the mesh size of the nets) are obvious candidates, but one can also consider the season or the actual location of the catch. Our database leads to 28 possible regressors (arising from six continuous variables and four categorical variables, whose 22 levels are treated separately), resulting in a set of 177 million possible linear regression models for the log-catch. Zero observations are modelled separately through a probit model. Inference is based on Bayesian model averaging, using a Markov chain Monte Carlo approach. Particular attention is paid to the prediction of catches for single and aggregated ships. [source] Individualized population pharmacokinetic model with limited sampling for cyclosporine monitoring after liver transplantation in clinical practiceALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 10 2007P. LANGERS Summary Background, We recently developed and validated limited sampling models (LSMs) for cyclosporine monitoring after orthotopic liver transplantation based on individualized population pharmacokinetic models with Bayesian modelling. Aim, To evaluate LSM in practice, and to seek optimal balance between benefit and discomfort. Methods, In 30 stable patients, more than 6 months after orthotopic liver transplantation, previously switched from trough- to 2 h post-dose (C2)-monitoring, we switched to 3-monthly LSM 0,1,2,3 h-monitoring. During 18 months we evaluated dose, creatinine clearance, calculated area under the curve, intra-patient pharmacokinetic variability and ability to assess systemic exposure by several previously validated LSMs. Results, Within patients, there was variability of cyclosporine-area under the curve with the same dose (CV of 15%). Compared to C2-monitoring, there was no significant difference in dose (P = 0.237), creatinine clearance (P = 0.071) and number of rejections. Some models showed excellent correlation and precision with LSM 0,1,2,3 h comparing area under the curves (0,2 h: r2 = 0.88; 0,1,3 h: r2 = 0.91; 0,2,3 h: r2 = 0.92, all P < 0.001) with no difference in advised dose. Conclusions, The limited sampling model, with only trough- and 2-h sampling, yields excellent accuracy and assesses systemic exposure much better than C2 with less bias and greater precision. Considering the calculated intra-patient variability, more precision is redundant, so LSM 0,2 h seems the optimal way of cyclosporine-monitoring. [source] RADIOCARBON-DATED DESTRUCTION LAYERS: A SKELETON FOR IRON AGE CHRONOLOGY IN THE LEVANTOXFORD JOURNAL OF ARCHAEOLOGY, Issue 3 2009ISRAEL FINKELSTEIN Summary We present a full-sequence radiocarbon-based chronological system for the Iron Age in the Levant, anchored on the dating of ten destruction layers for the years 1130,730 BC. We establish the sequence using two methods , the ,uncalibrated weighted average' and the Bayesian modelling. Utilizing four dating tools in combination , radiocarbon measurements, field stratigraphy, pottery typology and ancient Near Eastern historical records , facilitates solutions to chronological problems that are far beyond the resolving power of 14C dating alone. The results shed light on disputed issues related to biblical and ancient Near Eastern history, such as the expansion of the early Israelite polity from the highlands to the lowlands; the nature of the Shoshenq I campaign to Canaan; and the evolution of the conflict between northern Israel and Aram Damascus. [source] Advanced Statistical Analysis as a Novel Tool to Pneumatic Conveying Monitoring and Control Strategy DevelopmentPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3-4 2006Andrzej Romanowski Abstract Behaviour of powder flow in pneumatic conveying has been investigated for many years, though it still remains a challenging task both practically and theoretically, especially when considering monitoring and control issues. Better understanding of the gas-solids flow structures can be beneficial for the design and operation of pneumatic transport installations. This paper covers a novel approach for providing the quantitative description in terms of parameter values useful for monitoring and control of this process with the use of Electrical Capacitance Tomography (ECT). The use of Bayesian statistics for analysis of ECT data allows the direct estimation of control parameters. This paper presents how this characteristic parameters estimation can be accomplished without the need for reconstruction and image post processing, which was a classical endeavour whenever tomography was applied. It is achieved using a ,high-level' statistical Bayesian modelling combined with a Markov chain Monte Carlo (MCMC) sampling algorithm. Advanced statistics is applied to data analysis for measurements coming from the part of phenomena present in the horizontal section of pneumatic conveyor during slug formation. [source] Application of a Bayesian Approach to the Tomographic Analysis of Hopper FlowPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 4 2005Krzysztof Grudzien Abstract This paper presents a new approach to the analysis of data on powder flow from electrical capacitance tomography (ECT) using probability modelling and Bayesian statistics. The methodology is illustrated for powder flow in a hopper. The purpose, and special features, of this approach is that ,high-level' statistical Bayesian modelling combined with a Markov chain Monte Carlo (MCMC) sampling algorithm allows direct estimation of control parameters of industrial processes in contrast to usually applied ,low-level', pixel-based methods of data analysis. This enables reliable recognition of key process features in a quantitative manner. The main difficulty when investigating hopper flow with ECT is due to the need to measure small differences in particle packing density. The MCMC protocol enables more robust identification of the responses of such complex systems. This paper demonstrates the feasibility of the approach for a simple case of particulate material flow during discharging of a hopper. It is concluded that these approaches can offer significant advantages for the analysis and control of some industrial powder and other multi-phase flow processes. [source] VII,The Bayesian and the DogmatistPROCEEDINGS OF THE ARISTOTELIAN SOCIETY (HARDBACK), Issue 1pt2 2007Brian Weatherson It has been argued recently that dogmatism in epistemology is incompatible with Bayesianism. That is, it has been argued that dogmatism cannot be modelled using traditional techniques for Bayesian modelling. I argue that our response to this should not be to throw out dogmatism, but to develop better modelling techniques. I sketch a model for formal learning in which an agent can discover a posteriori fundamental epistemic connections. In this model, there is no formal objection to dogmatism. [source] HIERARCHICAL BAYESIAN MODELLING OF SOCIAL VARIATION IN THE AGE DEPENDENCE OF DISABILITY PREVALENCEAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 4 2005Patrick Graham Summary Motivated by a study of social variation in the relationship of functional limitation prevalence to age, this paper examines methods for modelling social variation in health outcomes. It is argued that, from a Bayesian perspective, modelling the dependence of functional limitation prevalence on age separately for each social group, corresponds to an implausible prior model, in addition to leading to imprecise estimates for some groups. The alternative strategy of fitting a single model, perhaps including some age-by-group interactions but omitting higher-order interactions, requires a strong prior commitment to the absence of such effects. Hierarchical Bayesian modelling is proposed as a compromise between these two analytical approaches. Under all hierarchical Bayes analyses there is strong evidence for an ethnic group difference in limitation prevalence in early- to mid-adulthood among tertiary-qualified males. In contrast, the single-model approach largely misses this effect, while the group-specific analyses exhibit an unrealistically large degree of heterogeneity in gender-education-specific ethnicity effects. The sensitivity of posterior inferences to prior specifications is studied. [source] | ||||||||||||||||