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Results for “probabilistic modelling”

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At least 469 records · Page 26Linked to original sources
PubMed2005

A gene selection algorithm based on the gene regulation probability using maximal likelihood estimation.

A novel gene selection algorithm based on the gene regulation probability is proposed. In this algorithm, a probabilistic model is established to estimate gene regulation probabilities using the maximum likelihood estimation method and then these probabilities are used to select key genes related by class distinction. The application on the leukemia data-set suggests that the defined gene regulation probability can identify the key genes to the acute lymphoblastic leukemia (ALL)/acute myeloid leukemia (AML) class distinction and the result of our proposed algorithm is competitive to those of the previous algorithms.

Acute Disease↗
PubMed1983

Interactions of acridine orange with nucleic acids. Properties of complexes of acridine orange with single stranded ribonucleic acid.

Interactions between acridine orange (AO) and nucleic acids (calf thymus DNA, and homoribo- and homodeoxyribo-polynucleotides) were studied in solutions containing ethanol as a cosolvent. Light absorption, scattering and luminescence were measured as a function of AO concentration at different dye/phosphate (D/P) ratios, and the data were analyzed using the McGhee-von Hippel probabilistic model of the polymer-ligand interactions. The absorption spectra of AO complexes with four homoribopolymers are presented. The intrinsic association constants and cooperativity coefficients of the formation of the complexes were calculated. The effects of ethanol (up to 35%, v/v) on these interactions were concentration dependent and may be extrapolated to zero concentration of this cosolvent. The possibility of destabilization of the double helix of nucleic acids by AO at high D/P ratios is discussed in light of the available thermodynamic data.

Acridine Orange↗
PubMed1991

An empirical analysis of likelihood-weighting simulation on a large, multiply connected medical belief network.

We are developing a probabilistic reformulation of the Quick Medical Reference (QMR) system. Our current probabilistic model of the QMR knowledge base of internal medicine consists of a two-level, multiply connected, belief network. Because of the size and connectivity of this belief network, most exact algorithms for calculating the posterior marginal probabilities of diseases are not applicable. In this paper, we analyze the convergence properties of an approximation algorithm, called likelihood-weighting simulation, on the QMR-DT belief network. Specifically, on two difficult diagnostic cases, we examine the effects of Markov blanket scoring, importance sampling, and self-importance sampling, demonstrating that the Markov blanket scoring and self-importance sampling significantly improve the convergence of the simulation on our model.

Algorithms↗
PubMed1978

The assessment of patient prognosis using an interactive computer program.

The use of chronic disease probabilistic models to calculate patient prognosis is presented. The method relies on the calculation of transition probabilities between discrete disease states from a patient data bank. Maximum likelihood estimates are used for each age and unwanted fluctuations are removed by a moving average. An interactive computer program was written and the method applied to the calculation of the probability of stroke and myocardial infarction for male patients on antihypertensive therapy. A clinician could obtain the prognostic information for a patient in less than one minute. Applications in medical student education are also discussed.

Cerebrovascular Disorders↗
PubMed1986

Maximum likelihood alignment of DNA sequences.

The optimal alignment problem for pairs of molecular sequences under a probabilistic model of evolutionary change is equivalent to the problem of estimating the maximum likelihood time required to transform one sequence to the other. When this time has been estimated, various alignments of high posterior probability may be written down. A simple model with two parameters is presented and a method is described by which the likelihood may be computed. Maximum likelihood estimates for some pairs of tRNA genes illustrate the method and allow us to obtain the best alignments under the model.

Animals↗
PubMed1996

Implicit redundant-targets effect in visual extinction.

Patients with left visual extinction as a result of unilateral right hemisphere damage were tested on a redundant-targets effect paradigm (RTE). LED-generated brief flashes were lateralized either to the left or to the right visual hemifield or presented bilaterally. Subjects were asked to press a key as fast as possible following either unilateral or bilateral stimuli and immediately afterwards to report on the number of stimuli presented. As previously found in normal subjects, bilateral stimuli were responded to faster than unilateral ones, and this was evidence of a RTE. The main thrust of this study was that extinction patients showed a RTE not only for correctly perceived bilateral stimuli but also in trials in which they extinguished the stimulus on the field contralateral to the lesion. This result is compatible with a preserved processing of the extinguished input at least up to the stage at which it may interact with the input from the normal side to yield a speeded motor response. Interestingly, the implicit redundancy gain of extinction patients was found to fit a coactivation (i.e. neural) rather than a probabilistic model.

Aged↗
PubMed1986

Analysis of the American Heart Association's recommendations for the prevention of infective endocarditis.

A probabilistic model analyzes the American Heart Association's (AHA) recommendations for the prevention of infective endocarditis (IE) of dental origin. The model, presented in the form of a flow chart, combines available data elements with the AHA recommendations; mortality serves as the sole valued outcome and payoff measure. The analysis shows that an annual death rate of 1.36 per million population is attributable to the antibiotics administered in an attempt to prevent IE, whereas not more than 0.26 annual deaths per million are traceable to IE of dental origin. Sensitivity and threshold analyses were conducted to determine the conditions under which the recommended prophylactic policy will prove beneficial. The model suggests that the standard AHA antibiotic regimen should be exploited only in IE susceptible patients belonging to the high risk categories and that its value in moderate, low, and negligible risk patients is doubtful. When the use of antibiotics is unavoidable, oral administration is the preferable route.

American Heart Association↗
PubMed1994

Predictive microbiology.

Predictive microbiology is based upon the premise that the responses of populations of microorganisms to environmental factors are reproducible, and that by considering environments in terms of identifiable dominating constraints it is possible, from past observations, to predict the responses of those microorganisms. Proponents claim that predictive microbiology offers many benefits to the practice of food microbiology, and there is growing interest internationally. This review considers the origins, benefits and approaches to predictive microbiology and critically considers limitations and potential solutions. It is suggested that the traditional delineation between kinetic and probabilistic models is artificial, and that the two approaches represent the opposite ends of a spectrum of modelling needs. It is concluded: that despite the complexity of many food systems predictive modelling can be successfully applied; that strategies based on predictive models can simplify problems and allow useful predictions and analyses to be made; that the full potential of the technique has not yet been realised; and that "predictive microbiology" may be seen as providing a rational framework for understanding the microbial ecology of food.

Bacteria↗
PubMedDate not supplied

Causal reasoning in computer programs for medical diagnosis.

Over the last decade substantial advances have been made in the use of causal pathophysiological knowledge in artificial intelligence-based programs for medical diagnosis. Various forms of causal representations have been used. They include probabilistic models, quantitative models, qualitative models, and models that describe causal relations at multiple levels of detail. This paper briefly analyses these methods using three representative systems. Outstanding problems and possible direction in further exploitation of causal reasoning for medical decision-support systems are also discussed.

Artificial Intelligence↗
PubMed1991

Strategies for graphical threshold determination.

Determining a threshold for a quantitative variable (arising in biological measurements for instance) is a common problem in medical decision making. We define seven commonly used strategies: each one leads to an optimal determination. To these strategies correspond relevant empirical curves: the ROC curve for strategies involving the sensitivity or the specificity, the predictive ROC curve (P-ROC curve) for strategies involving the positive and negative predicting values, and the well classified frequencies curve (WCF curve) for classification strategies where all misclassifications have the same importance. For one of the considered strategies, there also exists a theoretical formula for the optimal threshold, elicited within a classical probabilistic model, which gives a considerable advantage to this strategy. These strategies are applied to a stimulated example containing 702 cases, where we see that they lead to different optimal threshold values. Finally, we briefly review a practical application in the determination of thresholds for glycemia measurements, leading to the choice of one of them as the optimal one to consider in the gestational diabetes mellitus prediction.

Diagnosis, Computer-Assisted↗
PubMed1996

An epistemic utility approach to coordination in the Prisoner's Dilemma.

A probabilistic model of single-agent decision making is reviewed which accounts for considerations of both correctness and value. The formalism is then extended to decisions involving multiple agents by the use of a joint coordination function. Individual agents are characterized by factoring the coordination function in terms of conditional valuation and belief functions. This formalism is used to explore the parameter space in which cooperative decisions are possible in the Prisoner's Dilemma.

Cooperative Behavior↗
PubMed1987

Development and construct validity of a knee pain questionnaire.

A knee pain questionnaire, consisting of 15 dichotomous items, was submitted to an item analysis, based on the probabilistic model of Rasch. Five items had to be discarded but the remaining 10 constituted a homogeneous set, fit to be used as a scale. In particular, this meant that the total number of positive responses to the questionnaire could be used as a simple measure of the patients' knee pain. Further studies must be performed in order to analyze the reliability and empirical validity of the scale.

Humans↗
PubMed1995

DSM-III, DSM-IV and ICD-10 as severity scales for drug dependence.

The construct of illness severity serves many scientific and clinical functions. This study tested the performance as severity scales of three systems for diagnosing drug dependence--DSM-III, DSM-IV and ICD-10--in a multisite regional sample of 370 clinical subjects. Both lifetime and current severity of four drug problems--alcohol, cannabis, cocaine and opiate dependence--was studied in three stages: (a) item difficulty and internal consistency analysis; (b) probabilistic modeling of distribution behavior; and (c) concurrent validation against a set of independent measures. All three systems, for most drugs correlated with most test variables, had good to excellent concurrent validity. Unexpectedly, DSM-III showed in some instances better item behavior, composite score behavior and concurrent validity than the other systems, though DSM-IV and ICD-10 are based on slimmer generic algorithms, and may represent a good balance between simplicity and concurrent validity. Results suggest that the design of future diagnostic algorithms start at the item level and strive for moderate levels of both internal consistency and difficulty. Composite score distributions can then be modeled in field research, and necessary item corrections can be made before the algorithm is widely promulgated.

Adult↗
PubMed1988

Cell growth dynamics in long-term bladder carcinogenesis.

A biologically based probabilistic model of the carcinogenic process has been developed based on a two-stage theory of carcinogenesis. The model has been validated utilizing experimental urinary bladder carcinogenesis studies in the rat, with an emphasis on quantification of cell dynamics. Critical parameters tracked through this process include mitotic rates, cell loss and birth rates, and irreversible cellular transitions from normal to initiated to transformed states. Analyses demonstrate the sensitivity of tumor incidence to the timing and magnitude of changes to these cellular variables. Modeling has been applied to genotoxic compounds, such as N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide, and non-genotoxic compounds, such as sodium saccharin. For the latter compounds, complex administration regimens have been studied, including two-generation experiments, initiation-promotion experiments, and sodium saccharin administration following ulceration and regenerative hyperplasia. Modeling indicates that the effects of such compounds can be explained entirely on the basis of cytotoxicity and consequent hyperplasia. Quantitative modeling based on biological processes has the potential for direct application to carcinogenic risk assessment.

Cell Division↗
PubMed2004

Effects of incorrect computer-aided detection (CAD) output on human decision-making in mammography.

RATIONALE AND OBJECTIVES: To investigate the effects of incorrect computer output on the reliability of the decisions of human users. This work followed an independent UK clinical trial that evaluated the impact of computer-aided detection(CAD) in breast screening. The aim was to use data from this trial to feed into probabilistic models (similar to those used in "reliability engineering") which would detect and assess possible ways of improving the human-CAD interaction. Some analyses required extra data; therefore, two supplementary studies were conducted. Study 1 was designed to elucidate the effects of computer failure on human performance. Study 2 was conducted to clarify unexpected findings from Study 1. MATERIALS AND METHODS: In Study 1, 20 film readers viewed 60 sets of mammograms (30 of which contained cancer) and provided "recall/no recall" decisions for each case. Computer output for each case was available to the participants. The test set was designed to contain an unusually large proportion (50%) of cancers for which CAD had generated incorrect output. In Study 2, 19 different readers viewed the same set of cases in similar conditions except that computer output was not available. RESULTS: The average sensitivity of readers in Study 1 (with CAD) was significantly lower than the average sensitivity of read-ers in Study 2 (without CAD). The difference was most marked for cancers for which CAD failed to provide correct prompting. CONCLUSION: Possible automation bias effects in CAD use deserve further study because they may degrade human decision-making for some categories of cases under certain conditions. This possibility should be taken into account in the assessment and design of CAD tools.

Analysis of Variance↗
PubMed2006

Epidemiologic changes and economic burden of hypertension in Latin America: evidence from Mexico.

BACKGROUND: Costs of health services for hypertension and the financial consequences of epidemiologic changes in this disease are important concerns for health systems in Latin America. METHODS: We conducted longitudinal analyses of the economic impact of the epidemiologic changes on health care services for hypertension in the Mexican health care system. The cost evaluation method used was based on costing technique by production function and consensus techniques. To estimate the epidemiologic changes and financial consequences for the period 2005 to 2007, three probabilistic models were constructed according to the Box-Jenkins technique. RESULTS: If changes are not implemented in prevention programs to reduce the effects of current risk factors, there will be increases in the number of patients with hypertension as well as in the financial burden to treat the disease. The amount allocated for hypertension in 2007, which will be 6% to 8% of the total health budget, is US$ 2,486,145,132. Of these, US$ 1,178,725,132 will be direct costs and US$ 1,307,420,000 will be indirect costs. Regarding epidemiologic changes for 2005 v 2007 (P < .05), an increase is expected, although results show a greater increase in insured populations. CONCLUSIONS: If the risk factors and different health programs remain as they currently are, the economic impact of expected epidemiologic changes on the social security system will be particularly strong. Another relevant financial factor is the appearance of internal competition in the allocation of financial resources among the main providers of health services for hypertension; this factor becomes even more complicated within each provider.

Cost of Illness↗
PubMed2004

Fate of 130 hemagglutinins from different influenza A viruses.

In this study, we use our probabilistic models to analyze 130 hemagglutinins from different influenza A virus in order to gain the insight into their fate. The results provide three lines of evidence regarding the H5, H6, and H9 hemagglutinins: (i) the H5 hemagglutinins are more sensitive to mutations, this is the current state of the H5, H6, and H9 hemagglutinins; (ii) the H5 hemagglutinins had experienced more mutations in the past, this is the history of the H5, H6, and H9 hemagglutinins; and (iii) the H6 hemagglutinins has a bigger potential towards future mutations, this is the future of the H5, H6, and H9 hemagglutinins. Furthermore, this study gives two clues on the mutation tendency that is a degeneration process and the species susceptibility that is the chickens and ducks.

Hemagglutinins↗
PubMed2026

Metax enables accurate cross-domain taxonomic profiling of metagenomes.

Taxonomic profiling is fundamental to microbiome research, yet achieving high species-level accuracy remains challenging for complex communities that span bacteria, viruses, eukaryotes, and archaea, and these limitations are exacerbated in low-biomass, host-dominated samples. We introduce Metax, a cross-domain taxonomic profiler that integrates coverage-based probabilistic modeling with an expectation-maximization framework to distinguish true microbial signals from artifacts. Across >600 samples from host-associated, environmental, wastewater, and low-biomass clinical settings, including benchmarks with limited reference representation, Metax improved profiling accuracy, achieving on average 55% higher F1 scores and 45% lower Bray-Curtis dissimilarity than other methods. Moreover, this broad evaluation demonstrated that Metax resolved bacterial and viral signatures of peri-implantitis in oral microbiomes and revealed signals suggestive of reagent-borne contaminants and reference misassemblies in plasma-cell-free DNA. By leveraging genome-wide coverage evidence, Metax enables robust cross-domain profiling across diverse sample types and sequencing depths, including settings where reference databases are highly incomplete.

abundance estimation↗