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 595 records · Page 33Linked to original sources
PubMed1981

[Thymic seminomas (author's transl)].

The authors report on three cases of thymic seminoma treated between 1971 and 1981. These tumours, first described by Friedman in 1981. These tumours, first described by Friedman in 1951, belong to the group of extra-gonadal germinal tumours. They constitute about 2.5% of all thymic masses. The most probable pathogenic theory is abnormal migration of germinal cells from the vitelline sac to the embryonic thymus. Thymic seminomas are usually found in young men and are asymptomatic in 30% of the cases. Macroscopically, they present as solid tumours capable of invading the surrounding structures. Histologically, they resemble gonadal seminomas but are sometimes difficult to identify, which is unfortunate since treatment is dependent upon an accurate histological diagnosis. The authors suggest that the tumour should be biopsied under mediastinal fluoroscopy, so that an accurate histological diagnosis can be made. Treatment consists of surgical excision, which should be restricted and on no account should destroy important structures, completed by mediastinal radiotherapy. The mean survival time is 6.3 years; the 5-year survival rate is 75%.

Adult↗
PubMed1995

Aneuploidy occurrence in human tumours: a logical-automaton approach.

The search for new, reliable factors of prognosis in cancerology is sadly deficient at the present moment. Of these factors, the measurement of ploidy gives rise to considerable hope. Nevertheless, despite the impressive number of papers currently published, no general law seems to be emerging that associates the ploidy rate of a tumour with its clinical evolution in a patient. The purpose of the present work is firstly to use a logical automation to describe the cell cycle in terms of binary variables (the validation of the methodology), and secondly to demonstrate that a certain 'cancer logic' can be distilled, at least with respect to the genesis of DNA histograms among tumours.

Aneuploidy↗
PubMed1994

Mean-field calculations of chain packing and conformational statistics in lipid bilayers: comparison with experiments and molecular dynamics studies.

A molecular, mean-field theory of chain packing statistics in aggregates of amphiphilic molecules is applied to calculate the conformational properties of the lipid chains comprising the hydrophobic cores of dipalmitoyl-phosphatidylcholine (DPPC), dioleoyl-phosphatidylcholine (DOPC), and palmitoyl-oleoyl-phosphatidylcholine (POPC) bilayers in their fluid state. The central quantity in this theory, the probability distribution of chain conformations, is evaluated by minimizing the free energy of the bilayer assuming only that the segment density within the hydrophobic region is uniform (liquidlike). Using this distribution we calculate chain conformational properties such as bond orientational order parameters and spatial distributions of the various chain segments. The lipid chains, both the saturated palmitoyl (-(CH2)14-CH3) and the unsaturated oleoyl (-(CH2)7-CH = CH-(CH2)7-CH3) chains are modeled using rotational isomeric state schemes. All possible chain conformations are enumerated and their statistical weights are determined by the self-consistency equations expressing the condition of uniform density. The hydrophobic core of the DPPC bilayer is treated as composed of single (palmitoyl) chain amphiphiles, i.e., the interactions between chains originating from the same lipid headgroup are assumed to be the same as those between chains belonging to different molecules. Similarly, the DOPC system is treated as a bilayer of oleoyl chains. The POPC bilayer is modeled as an equimolar mixture of palmitoyl and oleoyl chains. Bond orientational order parameter profiles, and segment spatial distributions are calculated for the three systems above, for several values of the bilayer thickness (or, equivalently, average area/headgroup) chosen, where possible, so as to allow for comparisons with available experimental data and/or molecular dynamics simulations. In most cases the agreement between the mean-field calculations, which are relatively easy to perform, and the experimental and simulation data is very good, supporting their use as an efficient tool for analyzing a variety of systems subject to varying conditions (e.g., bilayers of different compositions or thicknesses at different temperatures).

1,2-Dipalmitoylphosphatidylcholine↗
PubMedDate not supplied

[The determination of the upper limits of year-round morbidity].

The use of K. Pearson's criterion has made it possible to establish that the empirical rows presenting the annual data on dysentery morbidity for each month during the period of many years correspond to binomial distribution. For this reason, the calculation of the highest limit of annual morbidity for many years should be made with the use of the formulae of great radices of quadratic inequation [formula: see text] used in mathematical statistics for the determination of the highest limits in binomial distribution. For the number of observations (n) not the number of inhabitants (which contradicts to the notion of observation in the theory of probability), but the number of minimal values of monthly morbidity, used for the calculation of the minimal average morbidity value omega or theta*, should be taken. To obtain objective results, the minimal average value omega or theta* and the ratio t2/2n must be of the same order, where t is the critical value of Student's criterion equal to 1.96.

Bacterial Infections↗
PubMedDate not supplied

1992 Bonica Lecture. Advances in chronic pain management since gate control.

OBJECTIVE: Two pain treatment systems that developed soon after the publication of the gate theory are probably a direct result of its publication: neuraxial opiate administration and electrical stimulation of the spinal cord and peripheral nerves and receptors. Although the use of these modalities has become widespread in managing chronic pain, there is disagreement about their long-term efficacy. This presentation will attempt to review the data regarding the mechanisms of action of these modalities and their efficacy in treating chronic pain of malignant and nonmalignant origin. DATA SOURCES: Data were derived almost entirely from original articles reporting experimental data from both animal and human studies and from series of patients undergoing treatment with the modalities reviewed. STUDY SELECTION: Where possible, controlled studies were selected. However, much of the available data regarding treatment results are uncontrolled. DATA EXTRACTION AND SYNTHESIS: Selected data from studies that were felt to be reasonably well conducted are presented or summarized. Because of the lack of control groups in many of the clinical trials, meta-analyses were not carried out. CONCLUSIONS: Long-term spinal opiate administration has been shown to be more effective than systemic opiates in some patients with cancer pain, but often must be combined with local anesthetics to provide satisfactory pain relief. Loss of effect over time is a significant problem. Since the identification of spinal opiate receptors and the introduction of spinally administered narcotics, a number of other receptors that are important in both sensitization and suppression of pain projection systems have been characterized. Agonists and antagonists to many of these receptors are being developed, and a few are available for clinical trials. Long-term electrical stimulation of the spinal cord produces substantial analgesia below the stimulated spinal segments in some patients with chronic pain. Although initial results are usually encouraging, long-term efficacy may be disappointing. It is postulated that analgesia associated with spinal stimulation is associated with both stimulation of large fiber ascending tracts and blockade of spinothalamic pathways. Transcutaneous electrical nerve stimulation (TENS) has come into widespread use in managing chronic pain and has had limited trials in cancer pain patients. It is well accepted by patients and physicians, but clinical studies of long-term efficacy have yielded variable results. The analgesic action is probably the result of both large afferent fiber activation and blockade of peripheral nociceptors.

Adrenergic alpha-Agonists↗
PubMed1997

Stochastic behavior of ion channels in varying conditions.

The opening and closing of a single ion channel can be described as the aggregation into two sets of states, open and shut, of an underlying Markov process with a finite number of states. In this paper we consider an inhomogeneous process due to changing physical conditions, in particular a pulse of activity in which the transition rates during the pulse differ from those obtaining both before and after the pulse. Outside the pulse the chain contains an absorbing shut subset, so that no activity is observed before the pulse and almost surely, at most a finite number of openings are generated by the pulse. We consider, in particular, the probability distribution of first latency (the time to first opening) and the distribution of the total activation time. We take into account the phenomenon of time-interval omission, when short open or shut times fail to be observed.

Animals↗
PubMedDate not supplied

Predicting clinical performance of radiologic technology students.

The lack of scientific studies on predictive criteria for evaluating the clinical potential of students in radiologic technology led to the current study. Students during a ten-year period was subjected to the ACT examinations. These scores were subsequently compared with the students' scores on the examination of The American Registry of Radiologic Technologists, high school grade point average and earned high-school grades in pertinent subjects to see if any predictive factors were evidenced. The result showed correlation of some of these factors with the Registry score of sufficient statistical significance to warrant using them as part of the process for selecting students for radiologic technology programs.

Clinical Competence↗
PubMed1998

Probability logic and probabilistic induction.

This article reviews some philosophical aspects of probability and describes how probability logic can give precise meanings to the concepts of inductive support, corroboration, refutation, and related notions, as well as provide a foundation for logically sound statistical inference. Probability logic also provides a basis for recognizing prior distributions as an integral component of statistical analysis, rather than the current misleading practice of pretending that statistics applied to observational data are objective. This basis is important, because the use of realistic priors in a statistical analysis can yield more stringent tests of hypotheses and more accurate estimates than conventional procedures.

Epidemiologic Studies↗
PubMed1998

Compression of strings with approximate repeats.

We describe a model for strings of characters that is loosely based on the Lempel Ziv model with the addition that a repeated substring can be an approximate match to the original substring; this is close to the situation of DNA, for example. Typically there are many explanations for a given string under the model, some optimal and many suboptimal. Rather than commit to one optimal explanation, we sum the probabilities over all explanations under the model because this gives the probability of the data under the model. The model has a small number of parameters and these can be estimated from the given string by an expectation-maximization (EM) algorithm. Each iteration of the EM algorithm takes O(n2) time and a few iterations are typically sufficient. O(n2) complexity is impractical for strings of more than a few tens of thousands of characters and a faster approximation algorithm is also given. The model is further extended to include approximate reverse complementary repeats when analyzing DNA strings. Tests include the recovery of parameter estimates from known sources and applications to real DNA strings.

Algorithms↗
PubMed2000

Signal detection theory in the 2AFC paradigm: attention, channel uncertainty and probability summation.

Neural implementation of classical High-Threshold Theory reveals fundamental flaws in its applicability to realistic neural systems and to the two-alternative forced-choice (2AFC) paradigm. For 2AFC, Signal Detection Theory provides a basis for accurate analysis of the observer's attentional strategy and effective degree of probability summation over attended neural channels. The resulting theory provides substantially different predictions from those of previous approximation analyses. In additive noise, attentional probability summation depends on the attentional model assumed. (1) For an ideal attentional strategy in additive noise, summation proceeds at a diminishing rate from an initial level of fourth-root summation for the first few channels. The maximum improvement asymptotes to about a factor of 4 by a million channels. (2) For a fixed attention field in additive noise, detection is highly inefficient at first and approximates fourth-root summation through the summation range. (3) In physiologically plausible root-multiplicative noise, on the other hand, attentional probability summation mimics a linear improvement in sensitivity up to about ten channels, approaching a factor of 1000 by a million channels. (4) Some noise sources, such as noise from eye movements, are fully multiplicative and would prevent threshold determination within their range of effectiveness. Such results may require reappraisal of previous interpretations of detection behavior in the 2AFC paradigm.

Attention↗
PubMed2006

Infinite populations and counterfactual frequencies in evolutionary theory.

One finds intertwined with ideas at the core of evolutionary theory claims about frequencies in counterfactual and infinitely large populations of organisms, as well as in sets of populations of organisms. One also finds claims about frequencies in counterfactual and infinitely large populations--of events--at the core of an answer to a question concerning the foundations of evolutionary theory. The question is this: to what do the numerical probabilities found throughout evolutionary theory correspond? The answer in question says that evolutionary probabilities are 'hypothetical frequencies' (including what are sometimes called 'long-run frequencies' and 'long-run propensities'). In this paper, I review two arguments against hypothetical frequencies. The arguments have implications for the interpretation of evolutionary probabilities, but more importantly, they seem to raise problems for biologists' claims about frequencies in counterfactual or infinite populations of organisms and sets of populations of organisms. I argue that when properly understood, claims about frequencies in large and infinite populations of organisms and sets of populations are not threatened by the arguments. Seeing why gives us a clearer understanding of the nature of counterfactual and infinite population claims and probability in evolutionary theory.

Animals↗