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At least 703 records · Page 39Linked to original sources
PubMed1999

The probability heuristics model of syllogistic reasoning.

A probability heuristic model (PHM) for syllogistic reasoning is proposed. An informational ordering over quantified statements suggests simple probability based heuristics for syllogistic reasoning. The most important is the "min-heuristic": choose the type of the least informative premise as the type of the conclusion. The rationality of this heuristic is confirmed by an analysis of the probabilistic validity of syllogistic reasoning which treats logical inference as a limiting case of probabilistic inference. A meta-analysis of past experiments reveals close fits with PHM. PHM also compares favorably with alternative accounts, including mental logics, mental models, and deduction as verbal reasoning. Crucially, PHM extends naturally to generalized quantifiers, such as Most and Few, which have not been characterized logically and are, consequently, beyond the scope of current mental logic and mental model theories. Two experiments confirm the novel predictions of PHM when generalized quantifiers are used in syllogistic arguments. PHM suggests that syllogistic reasoning performance may be determined by simple but rational informational strategies justified by probability theory rather than by logic.

Algorithms↗
PubMed2003

Stochasticity overrules the "three-times rule": genetic drift, genetic draft, and coalescence times for nuclear loci versus mitochondrial DNA.

Palumbi et al. (2001) proposed a "three-times rule" that uses mitochondrial DNA (mtDNA) sequences to predict probabilities of monophyly for nuclear loci (i.e., whether the alleles within a taxon coalesce with one another before they coalesce with alleles from a sister taxon). They use neutral coalescent theory to infer these probabilities from the ratio of interspecific divergence to intraspecific variation of mtDNA. We show that the estimated probabilities have very wide confidence intervals because of the inherent stochasticity of the mtDNA coalescent process. Under neutrality, the true probability of monophyly can be much higher, or much lower, than predicted by the three-times rule. We also review recent empirical and theoretical studies that refute neutrality-based predictions concerning mtDNA variation and divergence. We conclude that the three-times rule is neither a useful test for neutral molecular evolution nor a reliable guide to genealogical species.

Cell Nucleus↗
PubMed1996

On the value of clinical information. Is there a bridge between quantum theory and medical diagnosis?

This paper discusses the problems in assigning a precise value to an item (or group of items) of clinical information. Historical viewpoints are reviewed; the paper illustrates how determinist descriptive thinking has been overtaken by concepts of uncertainty and probability. Four equations are proposed outlining the factors which affect the value of clinical information. The validation of these equations and their implications is discussed. Parallels are drawn between the situation in theoretical physics a century ago and medical diagnostics today; and the central theme of uncertainty in both is emphasised. Finally, the need for further radical thinking is stressed.

Clinical Medicine↗
PubMed1998

Three types of IS-A statement in diagnostic classifications: three types of knowledge needed for development and maintenance.

Update mechanisms for diagnostic classifications should capture changes in medical knowledge but also allow for comparability across versions. This paper provides a basis for such a mechanism by describing types of IS-A statement and types of knowledge used in the construction of diagnostic classifications. Three types of IS-A statement are used: 'A is by definition a B', 'A is probably a B' and 'A is in theory necessarily a B'. Each relates to a different type of knowledge: knowledge of linguistic conventions, of probabilities, and of empirical theories and their status, respectively. Consequently, the development and maintenance of diagnostic classifications requires a collaboration of medical terminologists and medical scientists. The role of the latter is especially important during updating. Updating is necessitated by changing probabilities and by the introduction or changing status of empirical theories. The linguistic notion of hyponymy oversimplifies the issue.

Artificial Intelligence↗
PubMed2002

Relating interactions between neurofilaments to the structure of axonal neurofilament distributions through polymer brush models.

Neurofilaments (NFs) have been proposed to interact with one another through mutual steric exclusion of their unstructured C-terminal "sidearm" domains, producing order in axonal NF distributions and conferring mechanical strength to the axon. Here we apply theory developed for polymer brushes to examine the relationship between the brush properties of the sidearms and NF organization in axons. We first measure NF-NF radial distribution functions and occupancy probability distributions for adult mice. Interpreting the probability distributions using information theory, we show that the NF distributions may be represented by a single pair potential of mean force. Then, to explore the relationship between model parameters and NF architecture, we conduct two-dimensional Monte Carlo simulations of NF cross-sectional distributions. We impose purely repulsive interaction potentials in which the sidearms are represented as neutral and polyelectrolyte chains. By treating the NFs as telechelic polymer brushes, we also incorporate cross-bridging interactions. Both repulsive potentials are capable of reproducing NF cross-sectional densities and their pair correlations. We find that NF structure is sensitive to changes in brush thickness mediated by chain charge, consistent with the experimental observation that sidearm phosphorylation regulates interfilament spacing. The presence of attractive cross-bridging interactions contributes only modestly to structure for moderate degrees of cross-bridging and leads to NF aggregation for extensive cross-bridging.

Action Potentials↗
PubMed1987

Optimal dose distribution for eradication of heterogeneous tumours.

The traditional single hit multitarget theory has been applied on the probability of eradication of an organ or a tumor and the probability for causing complications in normal tissue. This simple theory predicts a decreasing possibility to achieve uncomplicated tumor control with increasing tumor size and maintained irradiation technique, because the control curve moves to higher doses and the complication curve to lower doses as the tumor size increases. This simple result is shown to be consistent with clinically observed dose response relations for small and large tumors. The optimal dose distribution for eradication of a heterogeneous tumor is derived on the assumption that a uniform minimal recurrence probability is most advantageous for the patient. The optimal dose distribution is proportional to the spatial variation of the local D0 value and the logarithm of the tumor cell density. Various techniques to measure the density of tumor cells and the different possibilities to deliver non-uniform dose distributions to the target volume are also discussed.

Dose-Response Relationship, Radiation↗
PubMed1999

On the theory of partially inbreeding finite populations. VI. The survival probability of a two-locus allele combination when there is partial selfing.

Consider a large population with two loci that may be linked, with one having alleles A and a and the second alleles B and b. Let there be initially one individual with genotype AB/ab in a population otherwise consisting of ab/ab individuals. We assume that AB/ab, Ab/aB, AB/aB, AB/Ab and AB/AB individuals have higher probabilities of survival to adulthood than individuals with genotype ab/ab. The probability that AB ultimately survives, if there is a positive probability of selfing, is calculated. To simplify calculations, it is assumed that the number of offspring produced by any individual follows a Poisson distribution and that genotypes of separate offspring are independent. If recombination is possible, we conclude that a population with a high probability of selfing is more likely to accumulate epistatically favorable genes than one reproducing largely by random mating. This advantage of selfing becomes more pronounced as the strength of selection in favor of AB increases.

Alleles↗
PubMed2002

Conditionals: a theory of meaning, pragmatics, and inference.

The authors outline a theory of conditionals of the form If A then C and If A then possibly C. The 2 sorts of conditional have separate core meanings that refer to sets of possibilities. Knowledge, pragmatics, and semantics can modulate these meanings. Modulation can add information about temporal and other relations between antecedent and consequent. It can also prevent the construction of possibilities to yield 10 distinct sets of possibilities to which conditionals can refer. The mental representation of a conditional normally makes explicit only the possibilities in which its antecedent is true, yielding other possibilities implicitly. Reasoners tend to focus on the explicit possibilities. The theory predicts the major phenomena of understanding and reasoning with conditionals.

Humans↗
PubMed2006

Vision as Bayesian inference: analysis by synthesis?

We argue that the study of human vision should be aimed at determining how humans perform natural tasks with natural images. Attempts to understand the phenomenology of vision from artificial stimuli, although worthwhile as a starting point, can lead to faulty generalizations about visual systems, because of the enormous complexity of natural images. Dealing with this complexity is daunting, but Bayesian inference on structured probability distributions offers the ability to design theories of vision that can deal with the complexity of natural images, and that use 'analysis by synthesis' strategies with intriguing similarities to the brain. We examine these strategies using recent examples from computer vision, and outline some important implications for cognitive science.

Algorithms↗
PubMed1994

Use of probabilistic expert judgment in uncertainty analysis of carcinogenic potency.

A new approach to characterizing the state of knowledge about carcinogenic potency is described. In this approach, the carcinogenic risk posed by a specific dose is characterized by a probability distribution, indicating the relative likelihood of different risk estimates. The approach utilizes expert judgment and a probability tree and is illustrated in a case study of chloroform exposure. Experts in cancer biology/toxicology, pharmacokinetics, and dose-response modeling were identified by a panel of science-policy specialists. In a workshop, experts reviewed the chloroform data, received training in probability elicitation, and constructed a consensual probability tree based on biological theories of cancer causation. Distributions of carcinogenic risk were developed based on the probability tree, chloroform data, judgmental probabilities provided by the experts, and classical statistical techniques. Risk distributions varied considerably between experts, with some predicting essentially no risk from 100 ppb chloroform in drinking water while other have at least some probability on risks generally considered of regulatory significance. Estimated human risk was much lower when extrapolating from liver tumors in animals than from kidney tumors. Issues of scientific disagreement leading to different risk distributions between experts are discussed. The resulting risk distributions are compared to standard EPA risk calculations for the same exposure scenario as well as to the expert judgement of epidemiologists about cancer risks of chlorinated drinking water. Issues in combining expert judgments are discussed, and several alternative methods are presented. Strengths and weaknesses of the distributional approach are discussed.

Animals↗
PubMed1991

Premelting thermal fluctuational base pair opening probability of poly(dA).poly(dT) as predicted by the modified self-consistent phonon theory.

We employ a mean field, modified, self-consistent phonon theory to evaluate the single base-pair opening rate and the probability of a base pair in the amino proton exchangeable state for the homopolymer poly(dA).poly(dT) at temperatures below the helix-coil transition region. Our calculated premelting single base-pair opening probabilities are in general agreement with several available experimental estimates from imino proton exchange and formaldehyde-induced DNA melting measurements. These calculated opening probabilities, however, are in disagreement with the prediction of the helix-coil transition theory. Possible reasons for the differences are discussed, especially the possible different definition of a meaningful open state in the premelting region. The premelting open state of the modified self-consistent phonon approximation theory seems to be appropriate to describe a solvent-accessible open configuration that is sufficient to facilitate important chemical reactions such as imino proton exchange and formaldehyde reaction with the bases. This can be compared with the completely unstacked open state of the helix-coil transition theory originally defined in the helix-coil transition region. We propose that the amino proton exchangeable state is different from the open state associated with melting and only involves the breaking of the amino interbase H bond. The agreement between the calculated and experimentally estimated probability of a base pair in the amino proton exchangeable state seems to support this hypothesis.

Base Composition↗