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Bayes' Theorem (Baye + theorem)
Selected AbstractsAn Assessment of the Potential Value of Elevated Homocysteine in Predicting Alcohol-withdrawal SeizuresEPILEPSIA, Issue 5 2006Stefan Bleich Summary:,Purpose: Higher homocysteine levels were found in actively drinking patients with alcohol dependence. Recent studies have shown that high homocysteine levels are associated with alcohol-withdrawal seizures. The aim of the present study was to calculate the best predictive cutoff value of plasma homocysteine levels in actively drinking alcoholics (n = 88) with first-onset alcohol-withdrawal seizures. Methods: The present study included 88 alcohol-dependent patients of whom 18 patients had a first-onset withdrawal seizure. All patients were active drinkers and had an established diagnosis of alcohol dependence, according to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). Sensitivity and specificity were calculated by using every homocysteine plasma level found in the study population as cut-off value. A Bayes theorem was used to calculate positive (PPV) and negative (NPV) predictive values for all cutoff values used. Results: The highest combined sensitivity and specificity was reached at a homocysteine plasma cutoff value of 23.9 ,M. Positive predictive values ranged from 0.23 to 0.745; the maximum was reached at a homocysteine plasma level of 41.7 ,M. Negative predictive values ranged from 0.50 to 0.935, with a maximum at a homocysteine plasma level of 15.8,M. Conclusions: Homocysteine levels above this cutoff value on admission are a useful screening tool to identify actively drinking patients at higher risk of alcohol-withdrawal seizures. This pilot study gives further hints that biologic markers may be helpful to predict patients at risk for first-onset alcohol-withdrawal seizures. [source] Accuracy of Spirometry in Diagnosing Pulmonary Restriction in Elderly PeopleJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 11 2009Simone Scarlata MD OBJECTIVES: To compare the accuracy of a diagnosis of pulmonary restriction made using forced vital capacity (FVC) less than the lower limit of normal (LLN) with the criterion standard diagnosis made using total lung capacity (TLC) less than the LLN in an elderly population. DESIGN: Retrospective analysis. SETTING: A teaching hospital. PARTICIPANTS: Five hundred sixty-four ambulatory and acute care hospital patients aged 65 to 96 underwent complete pulmonary function evaluation. MEASUREMENTS: Sensitivity, specificity, positive and negative predictive values (PPV, NPV) of diagnosis of pulmonary restriction defined as FVC less than the LLN were calculated in the overall sample and after stratification according to bronchial obstruction. Expected PPV and NPV at different background prevalence of true pulmonary restriction (5% and 15%) were calculated using the Bayes theorem. RESULTS: Low sensitivity (0.32) and high specificity (0.95) were found, with an area under the receiver operating characteristic curve (AUC) of 0.89. In participants without bronchial obstruction, specificity was even higher, although sensitivity decreased to 0.28 (AUC=0.92). The PPV was good (0.81), whereas with a low to moderate a priori probability (prevalence from 5% to 15%) the NPV was fair (,0.89). CONCLUSION: A reduction in FVC below LLN cannot reliably identify true pulmonary restriction in elderly people, confirming previous findings in the adult population. Normal FVC, instead, can effectively exclude pulmonary restriction regardless of the presence of bronchial obstruction when the a priori probability is low or moderately high. [source] A Methodology for Assessing Transportation Network Terrorism Risk with Attacker and Defender InteractionsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2010Pamela M. Murray-Tuite Decision makers need a methodology that can capture the complex attacker,defender interactions and help them understand the overall effects on the transportation system, as well as the consequences of asset failure. This article presents such a methodology, which uses probabilities of target,attack method combinations that are degree of belief based and updated using Bayes' Theorem after evidence of the attack is obtained. Monte Carlo simulation generates the probability of link capacity effects by sampling from distributions of capacity reductions due to preevent security measures, substitutions, target failure, and postevent security measures. The average capacity reduction for a particular target,attack method combination serves as an input to the traffic assignment,simulation package DYNASMART-P to determine travel time effects. The methodology is applied to a sample network based on the northern Virginia area. Results based on notional data indicated that preevent security measures reduced attack probabilities, but in some cases increased the mobility consequences. Thus, decision makers must carefully evaluate the effects of their decisions. [source] Bayes' Theorem to estimate population prevalence from Alcohol Use Disorders Identification Test (AUDIT) scoresADDICTION, Issue 7 2009David R. Foxcroft ABSTRACT Aim The aim in this methodological paper is to demonstrate, using Bayes' Theorem, an approach to estimating the difference in prevalence of a disorder in two groups whose test scores are obtained, illustrated with data from a college student trial where 12-month outcomes are reported for the Alcohol Use Disorders Identification Test (AUDIT). Method Using known population prevalence as a background probability and diagnostic accuracy information for the AUDIT scale, we calculated the post-test probability of alcohol abuse or dependence for study participants. The difference in post-test probability between the study intervention and control groups indicates the effectiveness of the intervention to reduce alcohol use disorder rates. Findings In the illustrative analysis, at 12-month follow-up there was a mean AUDIT score difference of 2.2 points between the intervention and control groups: an effect size of unclear policy relevance. Using Bayes' Theorem, the post-test probability mean difference between the two groups was 9% (95% confidence interval 3,14%). Interpreted as a prevalence reduction, this is evaluated more easily by policy makers and clinicians. Conclusion Important information on the probable differences in real world prevalence and impact of prevention and treatment programmes can be produced by applying Bayes' Theorem to studies where diagnostic outcome measures are used. However, the usefulness of this approach relies upon good information on the accuracy of such diagnostic measures for target conditions. [source] Using BiowinÔ, Bayes, and batteries to predict ready biodegradabilityENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2004Robert S. Boethling Abstract Wether or not a given chemical substance is readily biodegradable is an important piece of information in risk screening for both new and existing chemicals. Despite the relatively low cost of Organization for Economic Cooperation and Development tests, data are often unavailable and biodegradability must be estimated. In this paper, we focus on the predictive value of selected BiowinÔ models and model batteries using Bayesian analysis. Posterior probabilities, calculated based on performance with the model training sets using Bayes' theorem, were closely matched by actual performance with an expanded set of 374 premanufacture notice (PMN) substances. Further analysis suggested that a simple battery consisting of Biowin3 (survey ultimate biodegradation model) and Biowin5 (Ministry of International Trade and Industry [MITI] linear model) would have enhanced predictive power in comparison to individual models. Application of the battery to PMN substances showed that performance matched expectation. This approach significantly reduced both false positives for ready biodegradability and the overall misclassification rate. Similar results were obtained for a set of 63 pharmaceuticals using a battery consisting of Biowin3 and Biowin6 (MITI nonlinear model). Biodegradation data for PMNs tested in multiple ready tests or both inherent and ready biodegradation tests yielded additional insights that may be useful in risk screening. [source] Sociolinguistic inference and intercultural coorientation.HUMAN COMMUNICATION RESEARCH, Issue 3 2001A Bayesian model of communicative competence in intercultural interaction We present a model that examines the effects of cultural differences on coorientation (the ability of communicators to accurately encode and interpret the referential and relational meanings of messages). Intercultural coorientation is made problematic by the absence of certain shared communication system knowledge, which in same-culture interactions is used in the dynamic sociolinguistic negotiation of relational rights and obligations. We propose that the process of sociolinguistic negotiation of meanings relies fundamentally on probabilistic inference and have constructed a model based on Bayes' theorem. The model predicts the effects of the communication situation, communicator stereotypes and prejudice, and some other-culture speaker errors on conclusions the receiver draws about the message. Using the model, we distinguish between the ethnocentric error of interpreting a communication in terms of one's own culture and the error of not seeing the communication as diagnostic. Among our predictions are: (a) the less diagnostic the communication, the more impact cultural stereotypes will have on attributions; (b) although evidence of sociolinguistic incompetence sometimes causes misunderstanding, it sometimes prevents misunderstanding; (c) multiple consistent features make intentions clearer than would a single cue, but multiple features violating co-occurrence norms often lead to the attribution of incompetence. [source] An analytic model for the epoch of halo creationMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000W. J. Percival In this paper we describe the Bayesian link between the cosmological mass function and the distribution of times at which isolated haloes of a given mass exist. By assuming that clumps of dark matter undergo monotonic growth on the time-scales of interest, this distribution of times is also the distribution of ,creation' times of the haloes. This monotonic growth is an inevitable aspect of gravitational instability. The spherical top-hat collapse model is used to estimate the rate at which clumps of dark matter collapse. This gives the prior for the creation time given no information about halo mass. Applying Bayes' theorem then allows any mass function to be converted into a distribution of times at which haloes of a given mass are created. This general result covers both Gaussian and non-Gaussian models. We also demonstrate how the mass function and the creation time distribution can be combined to give a joint density function, and discuss the relation between the time distribution of major merger events and the formula calculated. Finally, we determine the creation time of haloes within three N -body simulations, and compare the link between the mass function and creation rate with the analytic theory. [source] Modelling Operational Losses: A Bayesian ApproachQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 5 2004Paolo Giudici Abstract The exposure of banks to operational risk has increased in recent years. The Basel Committee on Banking Supervision (known as Basel II) has established a capital charge to cover operational risks other than credit and market risk. According to the advanced methods defined in ,The New Basel Capital Accord' to quantify the capital charge, in this paper we present an advanced measurement approach based on a Bayesian network model that estimates an internal measure of risk of the bank. One of the main problems faced when measuring the operational risk is the scarcity of loss data. The methodology proposed solves this critical point because it allows a coherent integration, via Bayes' theorem, of different sources of information, such as internal and external data, and the opinions of ,experts' (process owners) about the frequency and the severity of each loss event. Furthermore, the model corrects the losses distribution by considering the eventual relations between different nodes of the network that represent the losses of each combination of business line/event type/bank/process and the effectiveness of the corresponding internal and external controls. The operational risk capital charge is quantified by multiplying the value at risk (VaR) per event, a percentile of the losses distribution determined, by an estimate of the number of losses that may occur in a given period. Furthermore, it becomes possible to monitor the effectiveness of the internal and external system controls in place at the bank. The methodology we present has been experimented as a pilot project in one of the most important Italian banking groups, Monte dei Paschi di Siena. Copyright © 2004 John Wiley & Sons, Ltd. [source] What is the optimal approach for using a direct amplification test in the routine diagnosis of pulmonary tuberculosis?RESPIROLOGY, Issue 4 2002A preliminary assessment Objective: The aim of this study was to determine the most appropriate strategy for the rapid diagnosis of pulmonary tuberculosis (PTB) using a nucleic acid amplification (NAA) test. Methodology: This was a prospective study of 128 adult patients in whom respiratory secretions were tested for Mycobacterium tuberculosis by the AMPLICOR assay. The basis for starting PTB treatment was noted for each patient. The optimal approach was determined by using Bayes' theorem to compare different combinations of pretest probability, smear results with the AMPLICOR test. Results: The incidence of PTB was 15.6%. In only one patient was treatment for PTB commenced because of a positive AMPLICOR result. The rest were managed according to the conventional approach which relied upon clinical judgment and direct smear. The optimal approach was to treat patients with high or intermediate pretest risk for PTB who returned positive AMPLICOR tests. The overall accuracies of the conventional approach, AMPLICOR test and optimal approach were 89.8, 95.3 and 96.1%, respectively. Conclusion: This small study suggests that NAA testing be limited to patients with high or intermediate pretest risk of PTB. In this group, positive results demand treatment while the management of those with negative results still relies on clinical judgment. [source] The utility of Bayes' theorem and Bayesian inference in veterinary clinical practice and researchAUSTRALIAN VETERINARY JOURNAL, Issue 12 2002IA GARDNER First page of article [source] | |||||||||||||