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 1,477 records · Page 82Linked to original sources
PubMed2004

Comparing categorization models.

Four experiments are presented that competitively test rule- and exemplar-based models of human categorization behavior. Participants classified stimuli that varied on a unidimensional axis into 2 categories. The stimuli did not consistently belong to a category; instead, they were probabilistically assigned. By manipulating these assignment probabilities, it was possible to produce stimuli for which exemplar- and rule-based explanations made qualitatively different predictions. F. G. Ashby and J. T. Townsend's (1986) rule-based general recognition theory provided a better account of the data than R. M. Nosofsky's (1986) exemplar-based generalized context model in conditions in which the to-be-classified stimuli were relatively confusable. However, generalized context model provided a better account when the stimuli were relatively few and distinct. These findings are consistent with multiple process accounts of categorization and demonstrate that stimulus confusion is a determining factor as 10 which process mediates categorization.

Decision Making↗
PubMed1992

Genetic structure of forensic populations.

DNA-based identification depends on the probability that two different individuals have the same phenotype, which is given by kinship theory. Together with the large and consistent body of evidence on human population structure, kinship theory provides a sound basis for forensic use of DNA markers.

DNA Fingerprinting↗
PubMed2000

The relevance of visual perception to cortical evolution and development.

The quality of brightness--perhaps the simplest visual attribute we perceive--appears to be determined probabilistically. In this empirical conception of the perception of light, the stimulus-induced activity of visual cortical neurons does not encode the retinal image or the properties of the stimulus per se, but associations (percepts) determined by the relative probabilities of the possible sources of the stimulus. If this theory is correct, the rationale for the prolonged postnatal construction of visual circuitry--and the evolution of this visual scheme--is to strengthen and/or create by activity-dependent feedback the empirically determined association on which vision depends.

Animals↗
PubMedDate not supplied

Application of statistical decision theory to treatment choices: implications for the design and analysis of clinical trials.

This paper explores the application of statistical decision theory to treatment choices in cancer which involve difficult value judgements in weighing beneficial and deleterious outcomes of treatment. Strengths and weaknesses of using decision theory are illustrated by considering the problem of selecting chemotherapy in advanced ovarian cancer. The paper includes an assessment of individual preferences in 27 volunteers and a discussion of some problems in utility assessment. An alternative approach, using threshold analysis, is presented in which the results of the decision analysis are expressed as a function of utility parameters. By knowing what sets of utilities favour each treatment, the assessment of patient preferences can then be focused on important differences of treatment options. The implications of these results for the design and analysis of clinical trials are discussed.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1985

Informational content of visual field location in glaucoma.

Information Theory has been applied to produce estimates of how valuable each stimulus location on the Friedmann Visual Field Analyser mk. II is in detecting early glaucomatous visual field defects. The results indicate that stimuli in the superior arcuate region of the visual field and in the inferior nasal quadrant give the maximum amount of information. Stimuli in the extreme superior field (beyond 20 degrees), the inferior temporal quadrant and around the physiological blind spot give the least amount of information. It is suggested that these results can be used to develop computerised techniques for the analysis of visual field data.

Adult↗
PubMed1981

SOD-A and chromosome 21. Conflicting findings in a familial translocation (9p24;21q214).

A balanced maternal chromosome translocation (9p24;21q214) resulted in two offspring with unbalanced karyotypes. One of these, a girl trisomic for both segment 9pter to 9p24 and segment 21pter to 21q214, was found to have a SOD-A activity not significantly different from those found in a group of five cases with trisomy 21. However, clinical evaluation of this girl revealed no symptoms of the Down syndrome. These findings suggest that, providing the gene dosage theory is correct, the gene for SOD-A is probably localized on chromosome 21 proximal to, or in, band q21.

Child↗
PubMed1993

Confounds of insensitivity and blind luck: statistical conclusion validity in stroke rehabilitation clinical trials.

We present theoretical analyses of some infrequently considered consequences of low power and quantitatively review power in 36 stroke rehabilitation clinical trials with multiple outcome variables. We demonstrate that low power affects the proportion of false alarms (type 1 errors) in the literature and probability of replication, not only the ability to detect true intervention effects; and that these consequences of low power are modulated by the probability that effective interventions have been preselected for study via theory and prior evidence. interventions have been preselected for study via theory and prior evidence. Rehabilitation trials showed low power to detect small, medium, or large treatment effects at alpha = 0.05 (0.09, 0.33, and 0.69, respectively). Effect sizes were generally small with adverse consequences on power. As expected, sample size was an important determinant of power. Power was lower for motor/reflex measures due to differences in sample sizes rather than effect sizes. These results and the conceptual analyses predict and address conflicting conclusions from stroke rehabilitation clinical trials.

Cerebrovascular Disorders↗
PubMed1989

Evaluation and optimization of diagnostic tests using receiver operating characteristic analysis and information theory.

We describe a mathematical technique and an associated computer program for comparing, evaluating and optimizing diagnostic tests. The technique combines receiver operating characteristic (ROC) analysis with information theory and cost-benefit analysis to accomplish this. The program is menu driven and highly interactive; it generates 13 possible user-determined ASCII disk files which can be easily converted to graphs. These graphs allow the user to make detailed comparisons among various diagnostic tests for all values of disorder prevalence, and also provide guidelines for cut-off selection in order to optimize tests. These techniques are applied to three published studies of the enzyme screening assay for diagnosis of infection with the HIV virus. We show how graphs produced by this program can be used to compare and optimize these diagnostic tests. The program is written for an IBM-compatible microcomputer running on a DOS operating system.

Clinical Laboratory Techniques↗
PubMed1986

Pulpitis and root canal therapy: is a diagnostic radiograph of value?

Historical data and a decision-flow diagram were used to analyze the informational value to be obtained from diagnostic radiographs in cases of pulpitis. It is recommended that preoperative radiographs be relegated to the category of nonroutine procedures and that the eccentric length-measurement radiograph be used as point of reference.

Bicuspid↗
PubMed1989

Measuring casemix specialization and the concentration of diagnoses in hospitals using information theory.

This paper examines the application of Information Theory to hospital discharge data. Information Theory offers a general methodology to compare sets of casemix proportions as a measure of (1) the concentration of admissions across hospitals for specific medical conditions and (2) specialization across diagnostic categories for individual hospitals. Unfortunately, Information Theory indices are difficult to interpret and subject to a potentially serious statistical bias when computed from discrete frequency counts, such as those obtained from discharge abstract data. The analysis presented here first clarifies the interpretation of Information Theory indices by relating them to formal statistical tests of hypotheses about hospital and diagnosis-specific patterns of admissions. It then documents the magnitude of the bias due to calculating indices from discrete frequency counts and proposes analytical strategies for dealing with this bias. Finally, the paper examines the empirical importance of the bias and the proposed adjustment, using data that are typical of those available for research on hospital casemix.

Costs and Cost Analysis↗
PubMed1990

Sensation-seeking: electrodermal and behavioral effects of stimulus content and intensity.

Although a number of studies support an arousal theory interpretation of differential sensation-seeking behavior, the conditions under which arousal correlates of this personality dimension are manifest is as yet unclear. Both theory and research suggest that among the external factors affecting the differential arousal response are stimulus relevance and stimulus intensity. The present study assessed the impact of these factors on both psychophysiological and behavioral responses. Subjects were preselected to represent the extremes of the sensation-seeking dimension, then exposed to auditory and visual presentations of a series of sexual and aggressive stimuli of systematically varied intensity. High sensation seekers gave larger amplitude SCRs to violent stimuli and larger initial responses to sexual stimuli presented visually, while verbal response intensities showed an opposite pattern. Overall, results provided support for an arousal theory interpretation of sensation-seeking, but suggested that the probability and magnitude of group differences is a somewhat complex function of stimulus intensity, stimulus modality, and perhaps other factors not yet assessed.

Adult↗
PubMed2006

The role of tunneling in enzyme catalysis of C-H activation.

Recent data from studies of enzyme catalyzed hydrogen transfer reactions implicate a new theoretical context in which to understand C-H activation. This is much closer to the Marcus theory of electron transfer, in that environmental factors influence the probability of effective wave function overlap from donor to acceptor atoms. The larger size of hydrogen and the availability of three isotopes (H, D and T) introduce a dimension to the kinetic analysis that is not available for electron transfer. This concerns the role of gating between donor and acceptor atoms, in particular whether the system in question is able to tune distance between reactants to achieve maximal tunneling efficiency. Analysis of enzyme systems is providing increasing evidence of a role for active site residues in optimizing the inter-nuclear distance for nuclear tunneling. The ease with which this optimization can be perturbed, through site-specific mutagenesis or an alteration in reaction conditions, is also readily apparent from an analysis of the changes in the temperature dependence of hydrogen isotope effects.

Amino Acid Sequence↗
PubMed2005

Electron channeling X-ray microanalysis for partially filled skutterudite structure.

Occupancy of Ce atoms on voids and coordinates of Sb atoms in a partially filled skutterudite CeFe6Ni2Sb24 were determined by the method for atomic location by channeling enhanced microanalysis (ALCHEMI), where characteristic X-ray intensities were measured and calculated at various electron incidence directions in a transmission electron microscope. The calculation was based on dynamical electron diffraction and inelastic scattering theories. The calculated intensities were significantly dependent on the occupation probability of Ce atoms on voids, the coordinates of Sb atoms and the sample thickness. Using the Levenberg-Marquardt least squares method, the occupation probability of Ce atoms and the coordinates of Sb atoms were 0.33 and 0 0.336 0.147, respectively.

Journal Article↗
PubMed2006

A competitive neural model of small number detection.

The ability to represent numbers is a key attribute for both humans and animals. Recent developments in the understanding of numerical processing has led to the proposal that humans utilise two independent representations of number, one for real numbers and another for integers. We describe a computational model of small number detection to explore the relationship between these core systems of number. We use a combination of unsupervised and supervised neural networks to simulate the interaction between the real and integer representations. For real values we use a self-organised spatial representation of number. For integer values we use a supervised network motivated by linguistic processing. During training and testing, the networks exhibit behavioural characteristics such as the number size and numerical distance effects. Each representation is combined using the mixture-of-experts architecture that allows us to model the subitization limit (the maximum number of visual stimuli that can be accurately quantified almost immediately) as the competitive allocation of representations for number detection, where the crossover point between deploying the real and integer representations of number is obtained through a process of learning. Our results suggest that the existence of two core systems of number is at least computationally plausible and further suggests that the subitization limit emerges through the interaction of spatial and linguistic numerical processing. This provides computational evidence for one way in which small and large numbers are related in humans.

Animals↗