SEARCH · PubMed Health

Results for “Probability”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,639 records · Page 91Linked to original sources

PubMed1992

Rates of decay for the survival probability of a mutant gene.

If qk is the extinction probability of a slightly supercritical branching process with offspring distribution [pkr:r = 0, 1, 2, ...], then it is shown that if supk sigma r r3pkr less than infinity, inf sigma 2k greater than 0, and mk----1, then 1-qk approximately 2(mk - 1)sigma -2k, where mk = sigma r rpkr, sigma 2k = k sigma r r2pkr - m2k. This provides a simple set of sufficient conditions for the validity of a conjecture of Ewens (1969) for the survival probability of a slightly advantageous mutant gene.

Gene Frequency↗

PubMed2005

[Probabilities cannot be calculated retrospectively--not even in the courtroom].

Chance events are part of everyday life, but coincidence of diseases often raises suspicions about hidden causes, for example when power lines are blamed for the geographical clustering of cancer. Recently, criminal procedures in the Netherlands have revolved around the question of whether statistical 'predictions' are a valid reason to hold a hospital nurse accountable for the occurrence of excess deaths during her duty hours, or a kindergarten employee for unexplained respiratory problems in several infants. In both cases, the appeals court judges did not accept the statistical 'argument' in the absence of other evidence. In the UK, however, Sally Clark's initial life sentence for the double murder of her 2 babies was largely based on 'probabilities in retrospect', put forward by the paediatrician Sir Roy Meadow as an expert witness. 4 years later she was acquitted, whereas Meadow was struck off the medical register on a charge of professional misconduct. There is no Bayesian or other mathematical solution to the problem of chance events. Only the detection of causal factors that are plausible and supported by new evidence can help to reinterpret coincidences as relationships. Scrupulous reasoning about probabilities is required, not only of physicians but also of judges and politicians.

Evidence-Based Medicine↗

PubMedDate not supplied

Testing deviation for a set of serial dilution most probable numbers from a Poisson-binomial model.

A serial dilution experiment estimates the microbial concentration in a broth by inoculating several sets of tubes with various amounts of the broth. The estimation uses the Poisson distribution and the number of tubes in each of these sets that show growth. Several factors, such as interfering microbes, toxins, or disaggregation of adhering microbes, may distort the results of a serial dilution experiment. A mild enough distortion may not raise suspicion with a single outcome. The test introduced here judges whether the entire set of serial dilution outcomes appears unusual. This test forms lists of the possible outcomes. The set of outcomes is declared unusual if any occurrence of an observed outcome is on the first list, or more than one is on the first or second list, etc. A similar test can apply when there are only a finite number of possible outcomes, and each outcome has a calculable probability, and few outcomes have tied probabilities.

Chemistry↗

PubMed2006

Separation of time scales, fixation probabilities and convergence to evolutionary stable states under isolation by distance.

To a first order of approximation, selection is frequency independent in a wide range of family structured models and in populations following an island model of dispersal, provided the number of families or demes is large and the population is haploid or diploid but allelic effects on phenotype are semidominant. This result underlies the way the evolutionary stability of traits is computed in games with continuous strategy sets. In this paper similar results are derived under isolation by distance. The first-order effect on expected change in allele frequency is given in terms of a measure of local genetic diversity, and of measures of genetic structure which are almost independent of allele frequency in the total population when the number of demes is large. Hence, when the number of demes increases the response to selection becomes of constant sign. This result holds because the relevant neutral measures of population structure converge to equilibrium at a rate faster than the rate of allele frequency changes in the total population. In the same conditions and in the absence of demographic fluctuations, the results also provide a simple way to compute the fixation probability of mutants affecting various ecological traits, such as sex ratio, dispersal, life-history, or cooperation, under isolation by distance. This result is illustrated and tested against simulations for mutants affecting the dispersal probability under a stepping-stone model.

Ecology↗

PubMedDate not supplied

[Correlation between the probability and dosage characteristics of safety in the processing of radioactive liquids].

The authors show it possible and expedient to use the probability characteristics for evaluation of the safe operation of radiation-dangerous plants. The calculated values of doses that might be following an accident at these plants fail to give an adequate account of reality since the doses are largely variates. To divide accidents into classes or levels, it is necessary to use the principle of non-excess of accident probability of the given class or level rather than the threshold principle of non-excess of doses.

Humans↗

PubMed2006

Efficient two-stage genome-wide association designs based on false positive report probabilities.

Despite recent advances, very-high-throughput (VHT) technologies capable of genotyping hundreds of thousands of SNPs in individual samples remain prohibitively expensive for the large studies necessary to screen substantial sections of the genome for variants with modest effects on disease risk. This paper presents a two-stage strategy, where a portion of available samples are genotyped with VHT technology, and a small number of the most promising variants are genotyped with standard high-throughput techniques in the remaining samples as an independent replication study. The sample sizes in the first and second stages and the corresponding significance levels are chosen to limit False Positive Report Probability (FPRP), while maximizing the number of Expected True Positives (ETPs). (The FPRP is the conditional probability that a marker is not truly associated with disease, given the a significant test for disease-marker association.) For a fixed budget, the two-stage strategy has greater power (a larger number of ETPs) than the single-stage strategy (where all subjects are genotyped using expensive VHT technology). Furthermore, concentrating on the FPRP leads to considerable savings relative to strategies designed to control the family-wise error (e.g. Bonferonni correction). The FPRP and number of ETPs can also accommodate researchers' prior beliefs about the number of causal loci and the magnitude of their effects. The expected number of false positives does not change if the true number and effects of causal loci differs from the specified prior (although the false discovery rate will vary), thus limiting the absolute amount of resources spent chasing "false leads."

Computational Biology↗

PubMed1991

The distribution of dioptric power: ellipsoids of constant probability density.

A sample from a population of dioptric powers may be used to estimate the distribution of dioptric powers in the population itself. This paper describes the method and shows further how one can obtain a graphical representation of the distribution. The graphical representation takes the form of ellipsoids of constant probability density. The centroid of each ellipsoid estimates the mean of the population while the size, shape and orientation show the extent and nature of the spread of the population. For illustrative purposes the theory is applied to measurements of refractive status before and after radial keratotomy. The ellipsoids are presented as stereo-pairs. They are useful for comparative and predictive purposes. Thus the ellipsoid that contains 95% of the population after surgery defines the set of refractive errors within which the refractive error of a particular eye can be expected to fall with a probability of 95%.

Humans↗

PubMed1990

[Mixing results of prospective and retrospective studies by objective decision analysis: evaluating probability by healthy human minds?].

The major shortcomings of formal decision analysis derive from the complexity of the clinical problem, behavioral qualities of the investigator and the method itself. It seems difficult to translate study results into a probability estimate for the problem in an individual patient. Therefore, probability assessments from the medical literature, one's own clinical experience and data sources should be combined. Decision analysis is not itself clinical reality but provides a model for thinking explicitly about the problem.

Clinical Competence↗

PubMed1991

Individual probability for onset of full-blown disease in patients infected with human immunodeficiency virus type 1.

Increased concentrations of neopterin, a marker for cell-mediated immune activation, and decreased numbers of CD4+ T cells, are predictors for progression of disease after infection with human immunodeficiency virus type 1. Previous studies have demonstrated different rates of onset of full-blown acquired immunodeficiency syndrome (AIDS) for groups of patients, defined by laboratory marker values, who were initially symptom-free. By re-analysis of one such study, we demonstrate how for an individual patient, the individual marker values, together with a prior risk estimate, can be converted into current or accumulated post-test probability of onset of AIDS at a certain time. We used a statistical technique suggested by Albert et al. (Clin Chem 1984;30:69-76), which allows incorporation of fixed and time-dependent covariates. Besides allowing individual projections, the method shows that the predictive abilities of CD4+ T cell numbers and of neopterin concentrations do not vary greatly with regard to time of observation; both laboratory markers independently modulate the underlying prior probability of AIDS onset, which is significantly increased with the passage of time.

Acquired Immunodeficiency Syndrome↗

PubMed1991

Predictive probability in clinical trials.

In a recent paper, Choi and Pepple (1989, Biometrics 45, 317-323) consider the use of predictive probabilities in the monitoring of clinical trials. In particular, they characterise the predictive probability as a "useful conservative measure" for monitoring purposes. In this note the nature and source of this "conservatism" are investigated.

Biometry↗

PubMedDate not supplied

Accuracy of Moyers' probability chart in a group of Thai subjects.

The objective of this study is to investigate the accuracy of Moyers' probability chart in predicting canine and premolar sizes from the sum of lower incisors in a group of Thai subjects. The fifty models of orthodontic patient, Faculty of dentistry, Mahidol University with no loss of tooth material mesio-distally, fully erupted permanent teeth, no mesial or distal restoration and normal tooth morphology were selected. The results of this study show that the under-estimation less than or equal to 2 mm. is 32 casts on upper (64%) and 28 casts on lower (56%) and the over estimation greater than 2 mm. is 16 casts on upper (32%) and 18 casts on lower (36%). In comparison of 14 models which have the same value of sum of lower incisors, there is a significant (alpha = 0.05) difference between the combined canine and premolar size of this study and Moyers' probability chart.

Humans↗

PubMedDate not supplied

[Influence of the probability of the random performance of an acquired reaction on the rate of the formation of an instrumental reflex].

Instrumental reflex formation in rats takes place more rapidly at high probability of random performance of instrumental reaction to light; however, it does not depend on the frequency of correct responses positive reinforcements (from 50 to 100%). In case of low probability, the learning process sharply slows down at 50% reinforcement of correct responses in comparison with 100% one.

Animals↗

PubMed1979

What is the probability that coronary artery surgery prolongs life?

Two-hundred and nine male patients who had coronary artery surgery from 1972 to 1974 at the Marshfield Clinic (MC) were compared with Veterans Administration (VA) coronary patients to determine the probability of coronary surgery prolonging life. The survival data includes operative and late cardiac and noncardiac deaths. Including the MC operative mortality rates but considering late noncardiac deaths withdrawn as alive at the time of death, the MC cumulative 5-year surgical survival rate is 93%. This is identical to predicted 93% 5-year survival rate for any man of 54.5 years, the average age of MC patients living in this geographic locale in 1973. Annual attrition rates, including the noncardiac deaths, are 1.4% for any man 1.5% per year for MC patients, based on MC 5-year survival data. It is probable that coronary surgery prolongs life by sharply reducing late cardiac deaths.

Coronary Artery Bypass↗

PubMedDate not supplied

[Individual behavior characteristics of dogs in conflict between the probability and the quality of reinforcement].

In experiments on dogs with equiprobable right and left reinforcements in the choice of feeder in conditions of free behaviour, direct correlation was found between the strength of the nervous system and the strategy of dogs behaviour. The dogs of strong type, despite the difference in equilibration and lability, manifested one, similar strategy of behaviour with dominating preferences, definite and goal-directed actions; the dogs of the weak type displayed another strategy, characterized by uncertainty, permanent hesitations in choice reaction. In situation of competition of probability and value of reinforcement, some different aspects of animals typology appeared, presumably connected with individual characteristics of functioning of four brain structures as a basis of types of higher nervous activity (frontal cortex, hippocampus, amygdala, hypothalamus). Behaviour of choleric and flegmatic was oriented to a high probability of events and that of sanguinic and melancholic--to a low one. Thus, "informational" and "motivational" factors of behaviour organization are connected with interaction of specialized brain macrostructures, and properties of this interaction become apparent in animals typology.

Animals↗

PubMed1988

An expository review of two methods of calculating the paternity probability.

There are two methods for calculating the posttests probability of paternity, viz., the nonexclusion probability method (E method) and the paternity index method (lambda method). This report reviews these two methods and explains the reasons behind them, in the hope that it might alleviate the current controversy between the advocates of these two methods. The emphasis throughout the paper is on exposition, using simple examples to illustrate certain principles or properties. A discussion follows the presentation of the two methods. The calculation of the paternity index is based on the genotype (or phenotype) of the accused man; and the value of the paternity index remains the same whether the accusation itself is true or false.

Biometry↗

PubMed1987

A contribution to the discussion of probabilities and human hair comparisons.

The paper by Gaudette and Keeping on "An Attempt at Determining Probabilities in Human Scalp Hair Comparison" in the Journal of Forensic Sciences (Vol. 19, No. 3, July 1974, pp. 599-606) has provoked considerable controversy. This paper highlights two of the sources of the controversy and shows how the probability, 1/4500, quoted by Gaudette and Keeping should be treated with caution. The necessity of the use of a likelihood ratio statistic is described. It is suggested that the hair examination form resulting from the responses to the questionnaire recently distributed by the authors and also the discussions at Quantico (Proceedings of the International Symposium on Forensic Hair Comparisons, 25-27 June 1985, Quantico VA) should be used to facilitate the collection of the data which will be necessary to enable a likelihood ratio statistic to be estimated effectively.

Forensic Medicine↗

PubMed1985

[Quantification of the biological effect of photons and electrons. 2. Probability of tumor destruction].

The study comprises two subjects: the probability of destruction of the irradiated tumor and the tumor immunogenicity and its changes in the course of radiotherapy. The distribution of Poisson was adopted in order to describe the tumor destruction. The probability of tumor destruction is analysed under consideration of the "critical cell number". The other part of the study deals with the immune system and its radiosensitivity. It is demonstrated that the patient's immune reaction can contribute to the tumor destruction if the irradiation planning is made in an adequate manner. Furthermore, different irradiation techniques are compared to one another. Pendulum therapy, especially with large fields, seems to be no superior method despite its geometric advantages.

Animals↗

PubMed1974

Elaboration of conditioned alimentary reflexes having different probabilities of reinforcement in rats with hippocampal lesions.

A motor alimentary conditioned reflex was elaborated in hippocampectomized and intact albino rats. Food reinforcement followed 100 percent, 50 percent, 33 percent or 25 percent of conditional stimulus presentations (click from a rotating food box). No differences were found in the rate of conditioned alimentary reflex elaboration between the hippocampectomized and control rats at 100 percent and 50 percent reinforcement, although the time-courses of formation of the conditioned reflex connection differed substantially. With low reinforcement probabilities (33 percent and 25 percent) the operated rats, unlike the intact ones, exhibited no adequate responses throughout the 10 experimental days. The results obtained corroborate an earlier suggestion that the hippocampus is involved in the organization of behavior the reinforcement probability of which is unknown or relatively low.

Acoustic Stimulation↗