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 667 records · Page 37Linked to original sources
PubMed2004

On the prediction of simultaneous inbreeding coefficients at multiple loci.

A new deterministic method for predicting simultaneous inbreeding coefficients at three and four loci is presented. The method involves calculating the conditional probability of IBD (identical by descent) at one locus given IBD at other loci, and multiplying this probability by the prior probability of the latter loci being simultaneously IBD. The conditional probability is obtained applying a novel regression model, and the prior probability from the theory of digenic measures of Weir and Cockerham. The model was validated for a finite monoecious population mating at random, with a constant effective population size, and with or without selfing, and also for an infinite population with a constant intermediate proportion of selfing. We assumed discrete generations. Deterministic predictions were very accurate when compared with simulation results, and robust to alternative forms of implementation. These simultaneous inbreeding coefficients were more sensitive to changes in effective population size than in marker spacing. Extensions to predict simultaneous inbreeding coefficients at more than four loci are now possible.

Data Interpretation, Statistical↗
PubMed1991

Influence of the local amino acid sequence upon the zones of the torsional angles phi and psi adopted by residues in proteins.

A set of parameters is derived to express the influence of the local amino acid sequence on the torsional angles phi and psi adopted by each residue in a protein. The formalism used, which is based on information theory, evaluates the probability for a given residue to be in a particular zone of the Ramachandran map. Comparisons with crystallographic structures suggest that the method can extract almost all of the available information from the local sequence and show that the local sequence carries only, on average, about 65% of the information necessary for specifying the conformation of a given residue in a protein. The rest is specified by long-range interactions that are specific for each protein fold. The parameters derived here provide a more detailed description of the prediction than other methods in allowing the allocation of the torsional angles for residues having an aperiodic structure and are intended to be used for directing the conformational search in a subsequent simulation of the three-dimensional structure. This method should also predict segments of the polypeptide chain that are the most stable and thus less sensitive to long-range interactions.

Amino Acid Sequence↗
PubMedDate not supplied

Rheological properties and molecular structure of tunicate cellulose in LiCl/1,3-dimethyl-2-imidazolidinone.

Solution properties and molecular structure of tunicate cellulose (TC), an animal cellulose from Halocynthia roretzi, were investigated in terms of rheological and dilute solution properties. The solvent used is 8 wt % LiCl/1,3-dimethyl-2-imidazolidinone (DMI). A solution of dissolving pulp (DP), derived from plant, was also used for comparison. The weight-average molecular weight, Mw, and the limiting viscosity number, [eta], of the TC were evaluated to be 413 x 10(6) and 2645 mL/g, respectively. The TC solution showed the same concentration dependence of GN (GN=5.49 x 10(6)phiw(2.1)4 Pa; phiw: weight fraction of cellulose in solution; GN: plateau modulus) as the DP solution and, moreover, also as the solution of cotton linter (CC) in 8 wt % LiCl/N,N-dimethylacetamide (DMAc). This exponent of 2.1(4) indicates that network structure by entanglements was formed in these solutions. According to the theory of Fetters et al., moreover, such identity means that all of these celluloses have the identical chain structure though their biological origins are far different. On the other hand, the phiw-dependence of eta0-etas (eta0=zero shear rate viscosity of solution; etas=solvent viscosity) was different between the TC and the DP solution in the semidilute regime: the TC solution exhibited eta0-etas proportional, variant phiw(7.5) and the DP solution eta0-etas proportional, variant phiw4. According to the theory of Doi-Edwards, this exponent of 4 (the DP solution) indicates that the DP behaves as flexible polymers in the solution. In contrast, the dependence for the TC solution seems unexplainable on the basis of molecular theories. This difference probably signifies the difference in the relaxation process or mechanism in entanglement systems.

Animals↗
PubMed2003

Doping-controlled ion diffusion in polyelectrolyte multilayers: mass transport in reluctant exchangers.

A new paradigm for nonlinear doping-controlled ion transport in soft condensed matter is presented, where the mobility of a minority "probe" ion is controlled by majority "salt" ion. The class of materials to which this paradigm applies is represented by ultrathin films of polyelectrolyte complexes, or multilayers. Intersite hopping of probe ions of charge nu occurs only when the charge of the destination site, produced by clustering of monovalent salt ions, is at least -nu, conserving electroneutrality. Salt ions are reversibly "doped" into the multilayer under the influence of external salt concentration. In situ ATR-FTIR reveals that the doping level, y, is proportional to salt concentration. Because hopping requires coincidence, or clustering, of salt, a strongly nonlinear dependence of flux, J, on salt concentration is observed: J approximately [NaCl](nu) approximately y(nu). This scaling was reproduced both by Monte Carlo simulations of ion hopping and by continuum probability expressions. The theory also predicts the observed scaling, though it underestimates the magnitude, of the strong selectivity of multilayers for ions of different charge.

Journal Article↗
PubMed2002

Transient resonance Raman and density functional theory investigation of the chlorine atom/carbon disulfide molecular complex involved in selective alkane photochlorination reactions.

The structure and bonding of the chlorine atom/carbon disulfide (CS(2)/Cl) complex involved in selective photochlorination reactions with alkanes was directly probed using transient resonance Raman spectroscopy. The experimental Raman vibrational frequencies were compared to those computed from density functional theory calculations for probable structures of the CS(2)/Cl complex. Our results indicate that the S [double bond] C [double bond] S...Cl complex species is responsible for the approximately 370 nm transient absorption band observed after ultraviolet photolysis of CCl(4) in the presence of CS(2). We discuss the structure and properties of the S [double bond] C [double bond] S...Cl complex and compare them with those for the related benzene/Cl and pyridine/Cl complexes.

Journal Article↗
PubMed2005

Predicting dynamic range and intensity discrimination for electrical pulse-train stimuli using a stochastic auditory nerve model: the effects of stimulus noise.

This work investigates dynamic range and intensity discrimination for electrical pulse-train stimuli that are modulated by noise using a stochastic auditory nerve model. Based on a hypothesized monotonic relationship between loudness and the number of spikes elicited by a stimulus, theoretical prediction of the uncomfortable level has previously been determined by comparing spike counts to a fixed threshold, Nucl. However, no specific rule for determining Nucl has been suggested. Our work determines the uncomfortable level based on the excitation pattern of the neural response in a normal ear. The number of fibers corresponding to the portion of the basilar membrane driven by a stimulus at an uncomfortable level in a normal ear is related to Nucl at an uncomfortable level of the electrical stimulus. Intensity discrimination limens are predicted using signal detection theory via the probability mass function of the neural response and via experimental simulations. The results show that the uncomfortable level for pulse-train stimuli increases slightly as noise level increases. Combining this with our previous threshold predictions, we hypothesize that the dynamic range for noise-modulated pulse-train stimuli should increase with additive noise. However, since our predictions indicate that intensity discrimination under noise degrades, overall intensity coding performance may not improve significantly.

Acoustic Stimulation↗
PubMed2003

Probabilistic framework for the estimation of the adult and child toxicokinetic intraspecies uncertainty factors.

Human health risk assessments use point values to develop risk estimates and thus impart a deterministic character to risk, which, by definition, is a probability phenomenon. The risk estimates are calculated based on individuals and then, using uncertainty factors (UFs), are extrapolated to the population that is characterized by variability. Regulatory agencies have recommended the quantification of the impact of variability in risk assessments through the application of probabilistic methods. In the present study, a framework that deals with the quantitative analysis of uncertainty (U) and variability (V) in target tissue dose in the population was developed by applying probabilistic analysis to physiologically-based toxicokinetic models. The mechanistic parameters that determine kinetics were described with probability density functions (PDFs). Since each PDF depicts the frequency of occurrence of all expected values of each parameter in the population, the combined effects of multiple sources of U/V were accounted for in the estimated distribution of tissue dose in the population, and a unified (adult and child) intraspecies toxicokinetic uncertainty factor UFH-TK was determined. The results show that the proposed framework accounts effectively for U/V in population toxicokinetics. The ratio of the 95th percentile to the 50th percentile of the annual average concentration of the chemical at the target tissue organ (i.e., the UFH-TK) varies with age. The ratio is equivalent to a unified intraspecies toxicokinetic UF, and it is one of the UFs by which the NOAEL can be divided to obtain the RfC/RfD. The 10-fold intraspecies UF is intended to account for uncertainty and variability in toxicokinetics (3.2x) and toxicodynamics (3.2x). This article deals exclusively with toxicokinetic component of UF. The framework provides an alternative to the default methodology and is advantageous in that the evaluation of toxicokinetic variability is based on the distribution of the effective target tissue dose, rather than applied dose. It allows for the replacement of the default adult and children intraspecies UF with toxicokinetic data-derived values and provides accurate chemical-specific estimates for their magnitude. It shows that proper application of probability and toxicokinetic theories can reduce uncertainties when establishing exposure limits for specific compounds and provide better assurance that established limits are adequately protective. It contributes to the development of a probabilistic noncancer risk assessment framework and will ultimately lead to the unification of cancer and noncancer risk assessment methodologies.

Adolescent↗
PubMed2004

Fuzzy logic and causal reasoning with an 'n' of 1 for diagnosis and treatment of the stroke patient.

The current scientific model for clinical decision-making is founded on binary or Aristotelian logic, classical set theory and probability-based statistics. Evidence-based medicine has been established as the basis for clinical recommendations. There is a problem with this scientific model when the physician must diagnose and treat the individual patient. The problem is a paradox, which is that the scientific model of evidence-based medicine is based upon a hypothesis aimed at the group and therefore, any conclusions cannot be extrapolated but to a degree to the individual patient. This extrapolation is dependent upon the expertise of the physician. A fuzzy logic multivalued-based scientific model allows this expertise to be numerically represented and solves the clinical paradox of evidence-based medicine.

Evidence-Based Medicine↗
PubMed1989

Teaching risk analysis.

The primary objective of this article is to present a method of risk analysis that can be taught by instructors of health service financial management as part of the discussion of the concepts of risk. First, the implications of risk and the need for risk analysis are discussed. Based on the theory of cumulative probability distributions, two criteria for capital investment decision making under risk are presented, and practical examples of how the criteria can be applied are provided. The paper concludes with a discussion of the limitations of the method of risk analysis and the educational implications of the method.

Decision Making↗
PubMed1995

[Genetics of vitiligo].

There are several arguments suggesting that vitiligo is a genetically dependent disease. Certain animals have comparable pigment disturbances (Smyth chickens, C57BL/6J-mi(vit)/mi(vit) mice and B light mice). Genetic studies have demonstrated that certain genes are crucial for the development of vitiligo. Familial cases and cases reported in twins are further arguments. There is a high risk for both children and siblings of a subject with vitiligo. Several HLA studies have been reported. Most show sporadic association between vitiligo and certain HLA groups, but there is no clear and regular association with any of the class I or II alleles. Intrinsic melanocyte anomalies which persist in cell culture also favour the genetic theory. Vitiligo is probably a polygenetic disease, simultaneous alterations in several genes either causing he disease or increasing susceptibility. One speculation would be that one or more genes are responsible for premature death of melanocytes. Likewise, genes affecting melanocyte growth either directly or via paracrine factors (genes coding for the keratinocyte melanotrophic factor, for example), and the combined effects of genes controlling autoimmune phenomena could be involved. Despite formal proof that vitiligo is genetically dependent, and despite rapid progress in molecular genetics, the gene or genes directly implicated in this dermatosis remain to be identified.

Animals↗
PubMed1974

Probability of gene fixation in an expanding finite population.

A mathematical theory was developed, based on diffusion models, that enables us to compute the probability of a rare mutant allele eventually spreading through a population when the population size changes with time. In particular, we elaborated the case in which the mutant allele has a definite selective advantage and the population expands following the logistic law. In this case, the probability of ultimate fixation of a single mutant is given by u = 2s(Z/N), where s is the selective advantage and Z/N is a factor by which the probability of fixation is modified through population expansion. Analytical expression was obtained for Z/N, and the validity of the formula for u was checked by Monte Carlo experiments.

Alleles↗
PubMed1999

When and why do people avoid unknown probabilities in decisions under uncertainty? Testing some predictions from optimal foraging theory.

When given a choice between two otherwise equivalent options - one in which the probability information is stated and another in which it is missing - most people avoid the option with missing probability information (Camerer & Weber, 1992). This robust, frequently replicated tendency is known as the ambiguity effect. It is unclear, however, why the ambiguity effect occurs. Experiments 1 and 2, which separated effects of the comparison process from those related to missing probability information, demonstrate that the ambiguity effect is elicited by missing probabilities rather than by comparison of options. Experiments 3 and 4 test predictions drawn from the literature on behavioral ecology. It is suggested that choices between two options should reflect three parameters: (1) the need of the organism, (2) the mean expected outcome of each option; and (3) the variance associated with each option's outcome. It is hypothesized that unknown probabilities are avoided because they co-occur with high outcome variability. In Experiment 3 it was found that subjects systematically avoid options with high outcome variability regardless of whether probabilities are explicitly stated or not. In Experiment 4, we reversed the ambiguity effect: when participants' need was greater than the known option's expected mean outcome, subjects preferred the ambiguous (high variance) option. From these experiments we conclude that people do not generally avoid ambiguous options. Instead, they take into account expected outcome, outcome variability, and their need in order to arrive at a decision that is most likely to satisfy this need.

Adult↗
PubMed1994

Prophylactic vaccines, risk behavior change, and the probability of eradicating HIV in San Francisco.

Theory is linked with data to assess the probability of eradicating human immunodeficiency virus (HIV) in San Francisco through the use of prophylactic vaccines. The necessary vaccine efficacy levels and population coverage levels for eradication are quantified. The likely impact of risk behavior changes on vaccination campaigns is assessed. The results show it is unlikely that vaccines will be able to eradicate HIV in San Francisco unless they are combined with considerable reductions in risk behaviors. Furthermore, if risk behavior increases as the result of a vaccination campaign, then vaccination could result in a perverse outcome by increasing the severity of the epidemic.

AIDS Vaccines↗
PubMed1997

Need probability affects retention: a direct demonstration.

Recent memory theory has emphasized the concept of need probability--that is, the probability that a given piece of learned information will be tested at some point in the future. It has been proposed that, in real-world situations, need probability declines over time and that the memory-loss rate is calibrated to match the progressive reduction in need probability (J.R. Anderson & Schooler, 1991). The present experiments were designed to examine the influence of the slope of the need-probability curve on the slope of the retention curve. On each of several trials, subjects memorized a list of digits, then retained the digits in memory for 1, 2, 4, 8, or 16 sec. Some trials ended with a recall test; other trials ended with the message, "no test." In Experiment 1, the likelihood of encountering a memory test (i.e., the need probability) was made to either increase or decrease as the retention interval increased; in Experiment 2, need probability either was flat (invariant across retention intervals) or decreased as the retention interval increased. The results indicated that the shape of the need-probability curve influenced the slope of the retention curve (Experiment 1) and that the effect became larger as the experimental session progressed (Experiment 2). The findings support the notion that memory adapts to need probabilities and that the rate of forgetting is influenced by the slope of the need-probability curve. In addition, all of the forgetting curves approximated a power function, suggesting that need probability influences the slope but not the form of forgetting.

Educational Measurement↗