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Results for “Probability Theory”

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At least 523 records · Page 29Linked to original sources
PubMed2005

What can one learn from two-state single-molecule trajectories?

A time trajectory of an observable that fluctuates between two values (say, on and off), stemming from some unknown multisubstate kinetic scheme, is the output of many single-molecule experiments. Here we show that when all successive waiting times along the trajectory are uncorrelated the on and the off waiting time probability density functions contain all the information. By relating the lack of correlation in the trajectory to the topology of kinetic schemes, we can immediately specify those kinetic schemes that are equally consistent with experiment, and cannot be differentiated by any sophisticated analyses of the trajectory. Correlated trajectories, however, contain additional information about the underlying kinetic scheme, and we consider the strategy that one should use to extract it.

Biophysical Phenomena↗
PubMed2003

Assessing the variability in GeneChip data.

INTRODUCTION: Oligonucleotide and cDNA microarray experiments are now common practice in biological science research. The goal of these experiments is generally to gain clues about the functions of genes by measuring how their expression levels rise and fall in response to changing experimental conditions. Measures of gene expression are affected, however, by a variety of factors. This paper introduces statistical methods to assess the variability of Affymetrix GeneChip data due to randomness. METHODS: The variation of Affymetrix's GeneChip signal data are quantified at both chip level and individual gene level, respectively, by the agreement study method and variance components method. Three agreement measurement methods are introduced to assess the variability among chips. Variation sources for gene expression data are decomposed into four categories: systematic experiment variation, treatment effect, biological variation, and chip variation. The focus of this paper is on evaluating and comparing the last two kinds of variations. RESULTS: Measurement of agreement and variance components methods were applied to an experimental data, and the calculation and interpretation were exemplified. The variability between biological samples were shown to exist and were assessed at both the chip level and individual gene level. Using the variance components method, it was found that the biological and chip variation are roughly comparable. The Statistical Analysis System (SAS) program for doing the agreement studies can be obtained from the correspondence author.

Algorithms↗
PubMed2005

Interpersonal comparison of subjective probabilities: toward translating linguistic probabilities.

Interpersonal variability in understanding linguistic probabilities can adversely affect decision making. Using the fact that everyone judges canonical probability events similarly in a manner consistent with axiom systems that yield a probability measure, we developed and tested a method for comparing the meanings of probability phrases across individuals. An experiment demonstrated that despite extreme heterogeneity in participants' linguistic probability lexicons, interpersonal similarity in phrase meaning is well predicted by phrase rank order within the lexicons. Thus, equally ranked phrases have similar meanings, and individual differences in linguistic probabilities may simply be explained by the phrases people use at each rank.

Decision Making↗
PubMed2005

Genetic risk estimation by healthcare professionals.

OBJECTIVES: To assess whether healthcare professionals correctly incorporate the relevance of a favourable test outcome in a close relative when determining the level of risk for individuals at risk for Huntington's disease. DESIGN AND SETTING: Survey of clinical geneticists and genetic counsellors from 12 centres of clinical genetics (United Kingdom, 6; The Netherlands, 4; Italy, 1; Australia, 1) in May-June 2002. Participants were asked to assess risk of specific individuals in 10 pedigrees, three of which required use of Bayes' theorem. PARTICIPANTS: 71 clinical geneticists and 41 other healthcare professionals involved in genetic counselling. MAIN OUTCOME MEASURES: Proportion of respondents correctly assessing risk in the three target pedigrees; proportion of respondents who were confident of their estimate. RESULTS: 50%-64% of respondents (for the three targets separately) did not include the favourable test information and incorrectly estimated the risks as being about equal to the prior risks; 77%-91% of these respondents were "sure" or "completely sure" that their estimations were correct. Twenty of the 112 respondents correctly estimated the risks for all three target pedigrees. CONCLUSIONS: Clinical geneticists and genetic counsellors frequently use prior risks in situations where Bayes' theorem should be applied, leading to overestimations of the risk for an individual.

Australia↗
PubMedDate not supplied

Applying total quality management (TQM) to health care administration.

Author Neil S. Fleming, Ph.D., ASQC, C.Q.E., approaches quality management from a more theoretical perspective, relating it to dimensions of predictability and responsiveness. He couples these with achieving the optimal balance between prevention, appraisal and failure with the goal of producing the lowest possible total quality costs.

Costs and Cost Analysis↗
PubMed1998

Automated acquisition of rules from clinical databases and its evaluation.

This paper presents an approach to induction of rules from databases using rough set model. The system was evaluated on three clinical databases, and induced results were compared with other conventional rule induction methods and medical experts' rules. The results show that the introduced results outperforms other methods, but that the description length of induced rules is a little short, compared with that of experts' rules, which suggests that experts' rules are combination of different kinds of reasoning, rather than simple classification.

Algorithms↗
PubMedDate not supplied

[Probabilistic description of the system "ligand-receptor"].

The theory of probabilities was used to describe the ligand-receptor interaction. Mean and variance of number ligand-receptor complexes are calculated. It is shown that the mean number of ligand-receptor complexes coincides with that obtained from the law of conservation masses. Proceeding from a ratio of mean and expectation it is shown that the variance of the number of ligand-receptor complexes should be taken into account with concentration of ligand-receptor complexes component less than 1 fmol.

Ligands↗
PubMed2000

[Determinants of health and health policies. Part I. Causality in medicine and its modeling].

Causality is the relation between the antecedent and consequence. Association between those two notions represents causal determinacy allowing understanding the subject, and the theory of probability, which deals with supposed contradiction of the chance and necessity. Understanding how health can be impaired enables to precede the disease, to change its natural history and to cure it. Causality in medicine is based on the conception of complex action of biological, psychological and social factors, which may have either positive or negative effects on our health. Empirical data forming basis for the search of aetiology represent a conglomerate of causal and indifferent elements. To identify them, various models are employed (black box, Rubik's cube, Chinese box, model of multiple accidental phenomena and others). Appropriate epidemiological methods enable not only to determine the preference, but also to signalize fallacies of looking for the origin of disease. Permanent problem of the medicine reveals the existence of the objective accident and the uncertainty in the professional decision.

Causality↗
PubMed2000

[How does model- and situation-specific lack of knowledge affect causal inferences?].

A model proposed by Thüring (1991) for inferences based on causal knowledge was empirically tested. According to this model, two variables affect the certainty with which a causal inference is concluded: insufficiency (model-specific uncertainty) and ambiguity (situation-specific uncertainty). Within an experiment these two variables were manipulated. Both had a very significant (p < .01) influence on causal inferences. In respect to its quantity, variation of ambiguity had the effect predicted in the model. Concerning insufficiency, distinct differences between predicted and empirical ratings were found. Reasons for these deviations and model modifications resulting therefrom are discussed.

Adult↗
PubMedDate not supplied

Causes and pathomechanisms of oesophageal varices development.

Portal hypertension is a common clinical syndrome with chronic liver diseases and is characterised by a pathological increase in portal pressure. Moreover, portal hypertension is associated with increased portal blood flow. Increased vascular resistance in portal hypertension is because of an increase in both intrahepatic and portosystemic collateral resistance. Chronic elevations in systemic and splanchnic blood flow have been documented as key elements of hyperdynamic circulatory state of hypertensive animals and humans. Peripheral vasodilatation initiates the development of the classic profile of decreased systemic elevated splanchnic blood flow and elevated cardia index that characterises this state. Portosystemic collaterals develop as a result of portal hypertension. This is the central pathophysiological event that leads to bleeding from oesophagogastric varices and portosystemic encephalopathy. Collateral vessels respond to various vasoconstrictors and vasodilators.--Varices in the distal 5 cm of the distal oesophagus are easily identified by endoscopy because of their superficial location in the lamina propria and therefore are must apt to bleed and why the current practise of endoscopic therapy is likely to be successful in obliterating the varices. In patients with oesophageal varices the dilated deep intrinsic veins displace the superficial venous plexus, assume a supepitheal position and are endoscopically visible as teleangiectasia, cherry red spots, red colour signs, hemocystic spots, red wale markings or varices on varices. As alternative endoscopic way of treatment the paravariceal injection has been propagated by our group thus preserving the pathophysiologic collaterals and preventing early new formation of collaterals and rebleeding. Pathophysiologically the concept of erosion has been abandoned and replaced by the explosion theory: bleeding probably occurs when the expanding force by pressure and flow can no longer be counter-balanced by the variceal wall tension; at this point the varices rupture and bleed. When the varix distension has increased, the radius has increased and the wall thickness decreased. Thus early diagnosis of patients with a high tendency to bleed can easily be made by endoscopy, measuring portal and/or oesophageal-variceal pressure and characteristising the chronic liver disease according to the Child-Pugh-classification.

Animals↗