Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Probability Theory”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,675 records · Page 93Linked to original sources
PubMed1999

Percolation thresholds, critical exponents, and scaling functions on planar random lattices and their duals.

The bond-percolation process is studied on periodic planar random lattices and their duals. The thresholds and critical exponents of the percolation transition are determined. The scaling functions of the percolating probability, the existence probability of the appearance of percolating clusters, and the mean cluster size are also calculated. The simulation result of the percolation threshold is p(c)=0.3333+/-0.0001 for planar random lattices, and 0.6670+/-0.0001 for the duals of planar random lattices. We conjecture that the exact value of p(c) is 1/3 for a planar random lattice and 2/3 for the dual of a planar random lattice. By taking possible errors into account, the results of our critical exponents agree with the values given by the universality hypothesis. By properly adjusting the metric factors on random lattices and their duals, we demonstrate explicitly that the idea of a universal scaling function with nonuniversal metric factors in the finite-size scaling theory can be extended to random lattices and their duals for the existence probability, the percolating probability, and the mean cluster size.

Journal Article↗
PubMed2005

Inconsistent probability estimates of a hypothesis: the role of contrasting support.

This paper studies consistency in the judged probability of a target hypothesis in lists of mutually exclusive nonexhaustive hypotheses. Specifically, it controls the role played by the support of displayed competing hypotheses and the relatedness between the target hypothesis and its alternatives. Three experiments are reported. In all experiments, groups of people were presented with a list of mutually exclusive nonexhaustive causes of a person's death. In the first two experiments, they were asked to judge the probability of each cause as that of the person's decease. In the third experiment, people were asked for a frequency estimation task. Target causes were presented in all lists. Several other alternative causes to the target ones differed across the lists. Findings show that the judged probability/frequency of a target cause changes as a function of the support of the displayed competing causes. Specifically, it is higher when its competing displayed causes have low rather than high support. Findings are consistent with the contrastive support hypothesis within the support theory.

Humans↗
PubMed2005

Relaxation in a glassy binary mixture: comparison of the mode-coupling theory to a Brownian dynamics simulation.

We solved the mode-coupling equations for the Kob-Andersen binary mixture using structure factors calculated from Brownian dynamics simulations of the same system. We found, as was previously observed, that the mode-coupling temperature T(c) inferred from simulations is about two times greater than that predicted by the theory. However, we find that many time-dependent quantities agree reasonably well with the predictions of the mode-coupling theory if they are compared at the same reduced temperature epsilon = (T - T(c))/T(c), and if epsilon is not too small. Specifically, the simulation results for the incoherent intermediate scattering function, the mean square displacement, the relaxation time, and the self-diffusion coefficient agree reasonably well with the predictions of the mode-coupling theory. We find that there are substantial differences for the non-Gaussian parameter. At small reduced temperatures the probabilities of the logarithm of single particle displacements demonstrate that there is hopping-like motion present in the simulations, and this motion is not predicted by the mode-coupling theory. The wave-vector-dependent relaxation time is shown to be qualitatively different from the predictions of the mode-coupling theory for temperatures where hopping-like motion is present.

Journal Article↗
PubMed1994

Community elderly. A nursing center's use of change theory as a model.

1. Despite functional limitations, independent elders usually voice satisfaction with the quality of their lives. However, life satisfaction can have a negative impact on self-care. As a result, older adults may become complacent about personal health practices. 2. Improvement in health behaviors and self-care practices increases the probability that older persons will be able to maintain independent functioning for a longer period. 3. Change theory can be used to determine client readiness to change health behaviors. The first stage, unfreezing, involves a desire for change. During the second stage, moving, new behaviors are identified that are perceived as problem-solving approaches. During the last stage, refreezing, new behaviors are integrated and internalized, while advice, reinforcement, and support are offered by the change agent. 4. Health screening alone is insufficient to create the discomfort necessary for change; unfreezing does not occur and health attitudes and behaviors remain unchanged. As valuable as health screening sessions are in raising participants' awareness, the study reported on suggests that it is the combination of health screening and nursing visits over time that creates the atmosphere in which change can occur.

Aged↗
PubMed2001

Covariate adjustment of event histories estimated from Markov chains: the additive approach.

Markov chain models are frequently used for studying event histories that include transitions between several states. An empirical transition matrix for nonhomogeneous Markov chains has previously been developed, including a detailed statistical theory based on counting processes and martingales. In this article, we show how to estimate transition probabilities dependent on covariates. This technique may, e.g., be used for making estimates of individual prognosis in epidemiological or clinical studies. The covariates are included through nonparametric additive models on the transition intensities of the Markov chain. The additive model allows for estimation of covariate-dependent transition intensities, and again a detailed theory exists based on counting processes. The martingale setting now allows for a very natural combination of the empirical transition matrix and the additive model, resulting in estimates that can be expressed as stochastic integrals, and hence their properties are easily evaluated. Two medical examples will be given. In the first example, we study how the lung cancer mortality of uranium miners depends on smoking and radon exposure. In the second example, we study how the probability of being in response depends on patient group and prophylactic treatment for leukemia patients who have had a bone marrow transplantation. A program in R and S-PLUS that can carry out the analyses described here has been developed and is freely available on the Internet.

Analysis of Variance↗
PubMed2000

Language evolution and information theory.

This paper places models of language evolution within the framework of information theory. We study how signals become associated with meaning. If there is a probability of mistaking signals for each other, then evolution leads to an error limit: increasing the number of signals does not increase the fitness of a language beyond a certain limit. This error limit can be overcome by word formation: a linear increase of the word length leads to an exponential increase of the maximum fitness. We develop a general model of word formation and demonstrate the connection between the error limit and Shannon's noisy coding theorem.

Biological Evolution↗
PubMed1997

A Dynamic Theory of Acquisition and Extinction in Operant Learning.

This article offers a new neural network framework for understanding both the transients and the asymptotes of operant (instrumental) learning. The theory shows that interplay between simple short and long-term memory mechanisms is sufficient to explain a large number of operant phenomena. It describes short- and long-term effects of reinforcement and how these effects modulate the operant response, how novel events are detected and processed, and how their consequences also modulate the operant response. The critical features of the present theory are: (1) reinforcement expectancy is defined as the aggregate prediction of response-reinforcement and stimulus-reinforcement associations; (2) reinforcement expectancy controls the rate of increase of the operant response; (3) the response is controlled by a behavioral inhibition unit which integrates the mismatch between expected (long-term) and experienced (short-term) events. The model predicts the general features of several operant phenomena such as response selection, development of preference under different manipulations of reinforcement probabilities, negative contrast, partial reinforcement extinction effect, and spontaneous recovery. Implications of the present theory for other operant conditioning phenomena, classical conditioning, and avoidance behavior are suggested. Copyright 1997 Elsevier Science Ltd. All Rights Reserved.

Journal Article↗
PubMed2006

From mere coincidences to meaningful discoveries.

People's reactions to coincidences are often cited as an illustration of the irrationality of human reasoning about chance. We argue that coincidences may be better understood in terms of rational statistical inference, based on their functional role in processes of causal discovery and theory revision. We present a formal definition of coincidences in the context of a Bayesian framework for causal induction: a coincidence is an event that provides support for an alternative to a currently favored causal theory, but not necessarily enough support to accept that alternative in light of its low prior probability. We test the qualitative and quantitative predictions of this account through a series of experiments that examine the transition from coincidence to evidence, the correspondence between the strength of coincidences and the statistical support for causal structure, and the relationship between causes and coincidences. Our results indicate that people can accurately assess the strength of coincidences, suggesting that irrational conclusions drawn from coincidences are the consequence of overestimation of the plausibility of novel causal forces. We discuss the implications of our account for understanding the role of coincidences in theory change.

Bayes Theorem↗
PubMedDate not supplied

Informational need of emotional stress.

According to the informational theory of emotions, emotions in humans depend on the power of some need (motivation) and the estimation by the subject of the probability (possibility) of the need satisfaction (the goal achievement). Low probability of need satisfaction leads to negative emotions, actively minimized by the subject. Increased probability of satisfaction, as compared to earlier forecast, generates positive emotions, which the subject tries to maximize, i.e. to enhance, to prolong, to repeat. The informational theory of emotions encompasses their reflective function, the laws of their appearance, the regulatory significance of emotions, and their role in organization of behavior. The level of emotional stress influences the operator's performance. A decrease in the emotional tonus leads to drowsiness, lack of vigilance, missing of significant signals and to slower reactions. An extremely high stress level disorganizes the activity, complicates it with a trend toward incorrect actions and reactions to insignificant signals (false alarms). The neurophysiological mechanisms of the influence of emotions on perceptual activity and operator performance as well as the significance of individuality are discussed.

Aerospace Medicine↗
PubMed1972

Duration discrimination: effects of probability of stimulus presentation.

Monkeys initiated a stimulus by pressing on the center of three levers and the stimulus terminated independently of behavior 60, 80, 90, or 100 sec later. Presses on the right lever were reinforced with food following the three briefer durations, and presses on the left lever, following the 100-sec duration. Incorrect responses produced a 10-sec timeout. Probability of presenting the 100-sec duration was manipulated in the range from 0.25 to 0.75, with the probabilities of the briefer durations remaining equal and summing to one minus the probability of the 100-sec duration. Percentage of responses on either side lever was functionally related to both the probability of presenting the 100-sec stimulus and to stimulus duration. An analysis of the data based on the theory of signal detection resulted in operating characteristics that were linear when plotted on normal-normal coordinates. The percentage of responses on either lever approximated the optimal values for maximizing reinforcement probability in each condition of the experiment.

Journal Article↗
PubMed2004

Relativistic electron localization and the lack of Zitterbewegung.

Using space-time resolved solutions to relativistic quantum field theory we analyze the electron-positron pair creation process from vacuum. For early times the entangled electron-positron wave function can be obtained analytically. We show that there are, in principle, no limitations to the localization length of an electron and demonstrate that its spatial probability density can be much narrower than the Compton wavelength. We also find that quantum field theory prohibits the occurrence of Zitterbewegung for an electron.

Journal Article↗
PubMed1976

The effects of gonadal irradiation in clinical radiation therapy: a review.

Recent improvements in radiation therapy of some malignancies in lower abdominal sites are leading to a prolongation of life in persons of child-bearing age. These successes require an evaluation of the possible undersirable consequences of the unavoidable gonadal irradiation that occurs in these cases. A review of radiobiological data from experimental animal studies and retrospective clinical studies suggests that in most instances human gonadal exposures in both sexes are insufficient to cause permanent sterility, because the exposures are fractionated and the total gonadal dose is much less than 600 rads. As a consequence, return of fertility must be anticipated, and the worrison questions of radiation-induced genetic damage in subsequent pregnancies must be addressed. This review did not substantiate this fear, because no case reports could be found of malformed infants among the progeny of previously irradiated parents. Some experimental studies suggest that radiation-damaged spermatogonia are self-destructive, but any evidence for this phenomenon in the ovary is nonexistent. We suggest that the difference between fact and theory here may be the mathematical result of the interplay of low probability for occurrences and the few patients who until now have survived long enough for study.

Abdominal Neoplasms↗
PubMedDate not supplied

Effect of nonparallel alternating fields on the mobility of DNA in the biased reptation model of gel electrophoresis.

Chromosome-size DNA molecules can now be separated using a variety of pulsed field gel electrophoresis techniques. In this article, we study the predictions of the biased reptation model concerning the effect of two pulsed fields, making an arbitrary angle, on the power of separation of gel electrophoresis. Separation is predicted to be largely enhanced for obtuse angles, in agreement with experiments. Interestingly, very large molecules, which are not separated by pulsed fields, are predicted not to migrate along the gel diagonal for fairly long periods of time. Finally, we discuss the optimization of these techniques using the results of the theory, and the limitations of the latter when fluctuations and intramolecular modes probably dominate the system.

Computer Simulation↗
PubMed2003

Drug induced nightmares--an etiology based review.

OBJECTIVE: Recent clinical trials have included patient complaints of nightmares as a category of reportable medication side effects. This study integrates that data into current experimental and theoretical research of drug effects that may alter dreaming and nightmares. The objective is to provide a clinical and theoretical framework useful in categorizing the potential and reported drug effects on nightmares. METHODOLOGY: This study reviews case reports and clinical trials that have reported nightmares or alterations in dreaming occurring secondary to medication usage. These data are analysed as to the probability of the drug/nightmare association, and integrated into current electrophysiological and neurochemical theories of dreaming and nightmares. RESULTS: Pharmacological agents affecting the neurotransmitters norepinephrine, serotonin and dopamine are clearly associated with patient reports of nightmares. Agents affecting immunological response to infectious disease are likely to induce nightmares in some patients. A possible association exists between reports of nightmares and agents affecting the neurotransmitters acetylcholine, GABA and histamine, as well as for some anesthetics, antipsychotics and antiepileptic agents. CONCLUSION: By utilizing our current experimental and theoretical knowledge base, the potential etiology of a majority of reported drug effects on nightmares can be classified. These data support current neurochemical theories of dreaming, as well as suggesting that the biochemical basis for dreaming and nightmare induction may be more complex than generally suggested.

Causality↗
PubMed2006

Bioenergetics-based matrix population modeling enhances life-cycle toxicity assessment of tilapia Oreochromis mossambicus exposed to arsenic.

The objective of this study was to integrate a bioenergetics-based modeling approach into a population stage structure to enhance life-cycle toxicity assessments of the effects of waterborne arsenic (As) on the population dynamics of the tilapia Oreochromis mossambicus. The proposed mathematical model links a Leslie matrix population model and a universal ontogenetic growth model embedding the population-level growth rate and stage-specific modes of toxic action. We present data analyses of key parameters and distributions and discuss the processes of data capture and analysis and the impact of acute/chronic As toxicity responses on population-level effects. We employed a three-parameter Hill equation model to describe the relationship between tilapia whole-body burden and mortality in order to estimate the probability of stage-specific vital rate of survival. Using the DEBtox theory, we distinguished three modes of toxic action (MOA): direct effects on growth and indirect effects via maintenance and food consumption on inhibition by arsenic of the growth of a tilapia population. The asymptotic population growth rate decreased from lambda = 1.0027 for the control group to lambda = 0.9935 for tilapia population exposed to 4 microg mL(-1) As, indicating a potential risk of population intrinsic growth rates for tilapia exposed to higher levels of waterborne As. Our results estimated that an As concentration of 1.02 microg mL(-1) would cause a 50% reduction in the tilapia population. We found that the interplay between external stressors of waterborne As concentration and internally generated modes of action decreasing feeding in the juvenile stage and increasing the maintenance cost in the adult stage had a pronounced influence on the population stage structure of tilapia.

Animals↗
PubMed1996

Spontaneous mutations in bacteria: chance or necessity?

Several investigators have recently reported that significant numbers of appropriately adapted mutants can be induced in bacterial and yeast strains by exposing stationary phase cells to specific environmental challenges. The resulting mutants are said to be both selection-induced and demonstrably non-random in origin; if this interpretation is correct, it is in direct conflict with the conventional neo-Darwinian view, which is that spontaneous mutants are truly random in origin and arise without the intervention of any overtly adaptive forces. We believe that there are alternative ways of accounting for the appearance of many (and probably all) of the additional mutants which proponents of the adaptive mutation theory claim are observed only after they applied the appropriate selective pressure. Having reviewed the available evidence, we consider that most (if not all) of the sorts of mutants which are said to have been induced following exposure of stationary-phase cells to intense selective pressure are equally likely to have been generated during the operation of certain well-known, conventional (and essentially random) cellular DNA repair processes. Evidence in support of our view can be found in the mainstream literature on the origins of spontaneous mutations. We also note that some of the molecular models which have recently been proposed to explain the production of selection-induced mutations preferentially (or even only) in genes of adaptive significance may turn out to be of considerable interest in their own right, even although the mutants whose origins they were intended to explain may turn out to have arisen in a manner which is totally independent of the conditions used for their selection.

Adaptation, Physiological↗