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At least 1,297 records · Page 72Linked to original sources
PubMed1989

Comparison of Bayesian with group sequential methods for monitoring clinical trials.

We describe some problems with applying methods based on classical sequential analysis to monitoring clinical trials. A Bayesian method is developed and the boundaries are compared with frequentist schemes. For the examples chosen, the Bayesian boundaries can be quite similar to those obtained from Pocock and O'Brien and Fleming (OBF) rules, depending on the choice of prior distribution. They converge less rapidly than OBF's but more rapidly than Pocock's. In general the Bayesian methods provide the same desirable features as frequentist methods, without sacrificing flexibility and simplicity of interpretation.

Bayes Theorem↗
PubMed1996

Long-run cooperation in the one-shot Prisoner's Dilemma: a hierarchic evolutionary approach.

This paper proposes a hierarchic evolutionary model leading to long-run cooperation in the Prisoner's Dilemma. The population is segmented into groups, and evolution and interaction take place 'in parallel' at two levels: (i) within groups at the lower level; (ii) among groups at the higher one. At each of these levels, what performs currently best tends to be imitated. On the other hand, occasionally, individuals also experiment with (or mutate to) some new strategy. If the number of groups is sufficiently large, the long-run (invariant) distribution of the process is shown to be concentrated on the cooperative outcome.

Animals↗
PubMed1992

Direct measurement of quantal changes underlying long-term potentiation in CA1 hippocampus.

The modification responsible for the long-term synaptic potentiation (LTP) that follows a brief conditioning period is not known. To elucidate this change, we have resolved quantal levels of transmission before and after induction of LTP. We find an increase both in the number of quanta released and in quantal amplitude, consistent with combined pre- and postsynaptic modifications. On average, about 60% of LTP can be accounted for by presynaptic enhancement. The increase in either quantal amplitude or quantal content varies significantly among different experiments, but is inversely correlated with its initial value. These results may help to reconcile the different views concerning the site of LTP expression.

Animals↗
PubMed2005

Causal heterogeneity in attention-deficit/hyperactivity disorder: do we need neuropsychologically impaired subtypes?

Before assigning full etiologic validity to a psycopathologic disorder, disease theory suggests that a causal dysfunction in a mechanism within the affect individuals must be identified. Existing theories on attention-deficit/hyperactivity disorder (ADHD) suggest such dysfunctions in cognitive, neuropsychological, or motivational processes in the child. To date, researchers have tested these theories by comparing groups with DSM-defined ADHD to children without ADHD. Using executive functioning as an illustration of an issue that exists across all such theories, this article describes substantial overlaps in the group performance data. Thus only a subgroup may have executive deficits. Noted are other supportive data suggesting multiple pathways to ADHD. The article explores implications and recommends that future theory and research give more consideration to the probability that only a subset of behaviorally defined children will have a deficit in a given neurocognitive mechanism believed to contribute to the disorder. Creation of a provisional set of criteria in DSM-V for defining an "executive deficit type" could stimulate research to validate the first etiologic subtype of ADHD and spur the development of more sophisticated causal models, which in the longer term may give clinicians ways to target and tailor treatments.

Attention Deficit Disorder with Hyperactivity↗
PubMed2006

Control of Boolean networks: hardness results and algorithms for tree structured networks.

Finding control strategies of cells is a challenging and important problem in the post-genomic era. This paper considers theoretical aspects of the control problem using the Boolean network (BN), which is a simplified model of genetic networks. It is shown that finding a control strategy leading to the desired global state is computationally intractable (NP-hard) in general. Furthermore, this hardness result is extended for BNs with considerably restricted network structures. These results justify existing exponential time algorithms for finding control strategies for probabilistic Boolean networks (PBNs). On the other hand, this paper shows that the control problem can be solved in polynomial time if the network has a tree structure. Then, this algorithm is extended for the case where the network has a few loops and the number of time steps is small. Though this paper focuses on theoretical aspects, biological implications of the theoretical results are also discussed.

Algorithms↗
PubMed1988

Evolutionarily stable strategies for a finite population and a variable contest size.

This paper presents a generalization of Maynard Smith's concept of an evolutionarily stable strategy (ESS) to cover the cases of a finite population and a variable contest size. Both equilibrium and stability conditions are analysed. The standard Maynard Smith ESS with an infinite population and a contest size of two (pairwise contests) is shown to be a special case of this generalized ESS. An important implication of the generalized ESS is that in finite populations the behaviour of an ESS player is "spiteful", in the sense that an ESS player acts not only to increase his payoff but also to decrease the payoffs of his competitors. The degree of this "spiteful" behaviour is shown to increase with a decrease in the population size, and so is most likely to be observed in small populations. The paper concludes with an extended example: a symmetric two-pure-strategies two-player game for a finite population. It is shown that a mixed strategy ESS is globally stable against invasion by any one type of mutant strategist. The condition for the start of simultaneous invasion by two types of mutant is also given.

Behavior↗
PubMed2004

[Pharmacology and classification of cyclooxygenase inhibitors].

The discovery of at least two cyclooxygenase (COX) isoenzymes had two major consequences: i) to give a new impetus to the research on lipid metabolism, giving rise to the crystallization of these peculiar membrane enzymes, the characterization of their active sites and their gene regulation, and the identification of new metabolic pathways; ii) the development of new NSAIDs aimed to have an improved safety profile, the coxibs. These drugs are defined by their COX-2 selectivity which is supported by a negligible inhibitory potency on platelet COX-1 in vitro and ex vivo after oral intake of maximal therapeutic doses. However, the coxibs marketed in France (celecoxib, rofecoxib, parecoxib) are not equivalent in terms of selectivity and some drugs developed by pharmaceutical companies (etoricoxib, lumiracoxib) will be even more selective for COX-2. These "new" coxibs are the final step in the theory of COX-2 selectivity and they will probably be helpful to better define the limitations of the therapeutic concept based on a selective inhibition of this iso-enzyme.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

Algebraic geometrical methods for hierarchical learning machines.

Hierarchical learning machines such as layered perceptrons, radial basis functions, Gaussian mixtures are non-identifiable learning machines, whose Fisher information matrices are not positive definite. This fact shows that conventional statistical asymptotic theory cannot be applied to neural network learning theory, for example either the Bayesian a posteriori probability distribution does not converge to the Gaussian distribution, or the generalization error is not in proportion to the number of parameters. The purpose of this paper is to overcome this problem and to clarify the relation between the learning curve of a hierarchical learning machine and the algebraic geometrical structure of the parameter space. We establish an algorithm to calculate the Bayesian stochastic complexity based on blowing-up technology in algebraic geometry and prove that the Bayesian generalization error of a hierarchical learning machine is smaller than that of a regular statistical model, even if the true distribution is not contained in the parametric model.

Algorithms↗
PubMed1999

Patent guide for miniaturists.

Inventors who are mystified by the concepts of "nonobviousness" and "enablement" may be surprised to find that the two concepts have a simple explanation in information theory. Viewing an invention as a low-probability, high-information event helps explain why an invention that appears inventive (nonobvious) to an inventor may appear obvious to a patent examiner, and suggests some strategies for overcoming the examiner's bias. Viewing enablement as a means of increasing the probability that a claimed invention can be practiced successfully helps in understanding how to support a broad claim effectively by virtual or "paper" patenting. The notion of entropy, or mean information content, as applied to inventions, may guide inventors in their search for new inventions.

Journal Article↗
PubMed2002

Adaptation, punctuation and information: a rate-distortion approach to non-cognitive 'learning plateaus' in evolutionary process.

We extend recent information-theoretic phase transition approaches to evolutionary and cognitive process via the Rate Distortion and Joint Asymptotic Equipartition Theorems, in the circumstance of interaction with a highly structured environment. This suggests that learning plateaus in cognitive systems and punctuated equilibria in evolutionary process are formally analogous, even though evolution is not cognitive. Extending arguments by Adami et al. (2000), we argue that 'adaptation' is the process by which a distorted genetic image of a coherently structured environment is imposed upon a species.

Adaptation, Biological↗
PubMed2004

Partition-edit-count: naive extensional reasoning in judgment of conditional probability.

The authors provide evidence that people typically evaluate conditional probabilities by subjectively partitioning the sample space into n interchangeable events, editing out events that can be eliminated on the basis of conditioning information, counting remaining events, then reporting probabilities as a ratio of the number of focal to total events. Participants' responses to conditional probability problems were influenced by irrelevant information (Study 1), small variations in problem wording (Study 2), and grouping of events (Study 3), as predicted by the partition-edit-count model. Informal protocol analysis also supports the authors' interpretation. A 4th study extends this account from situations where events are treated as interchangeable (chance and ignorance) to situations where participants have information they can use to distinguish among events (uncertainty).

Humans↗