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PubMed1997

P300 sequence effects, probability, and interstimulus interval.

Probability and interstimulus interval effects on P3(00) event-related potential (ERP) stimulus sequences were examined in 2 experiments. ERPs were elicited with an auditory-discrimination paradigm in which subjects were instructed to detect target stimuli from a series of target (T) and standard (S) tones that were varied by randomly presenting 1 of 4 sequence patterns (SS, TS, TT, ST). Experiment 1 manipulated target stimulus probability as either 0.33 or 0.67; Experiment 2 kept target probability at 0.33 and manipulated the interstimulus interval (ISI) as either 2 or 6 s. Increases in target stimulus probability produced smaller P300 amplitudes that were additive with stimulus sequence type. ISI did not reliably affect P300 amplitude, although ISI interacted with stimulus sequence. P300 latency from the stimulus sequences was influenced weakly by the probability and ISI factors, with few consistent sequence effects obtained for the N1, P2, and N2 potentials. The results suggest that even relatively short sequences can affect P300 amplitude in the same way as longer sequences: as the number of standard stimuli preceding the target increased, P300 amplitude increased. The theoretical implications of the findings are discussed in the context of applied testing situations.

Adolescent↗

PubMed2001

Sign of lipid peroxidation as measured in the urine of patients with probable Alzheimer's disease.

Free radical-induced oxidative damage may be involved in the neurodegenerative process associated with Alzheimer's disease (AD). 8-Isoprostaglandin F(2alpha) (iPF(2alpha)-III) is an isoprostane derived from free radical-induced non-enzymatic oxidation of arachidonic acid. It is formed in vivo and is an indicator of lipid peroxidation. Measurements were made of iPF(2alpha)-III in the urine of patients with mild to moderate dementia associated with probable AD and compared to those in the urine of non-demented subjects, who were similar in age and gender. 2,3-Dinor thromboxane B(2) (dinor TXB(2)), a urinary metabolite of TXB(2) was also measured, and served as an indicator of the enzymatic transformation of a product of arachidonic acid. Enzyme linked immunoassays were used to measure iPF(2alpha)-III and dinor TXB(2) in the urine. The concentration of iPF(2alpha)-III was significantly elevated in urine of patients assessed to have mild to moderate dementia as compared to non-demented patients. The concentration of urinary dinor TXB(2) was also significantly elevated in the patients with dementia and probable AD as compared to the non-demented subjects. There was considerable overlap of values obtained for demented and non-demented patients for iPF(2alpha)-III and dinor TXB(2), respectively. The observed elevation of iPF(2alpha)-III suggests that patients with mild to moderate dementia associated with probable AD are experiencing significant oxidative stress. This finding is consistent with current data suggesting that oxidative stress may be occurring in patients with dementia and probable AD. The increase of dinor TXB(2) may indicate that enzymatic processes related to the metabolism of arachidonic acid-derived products are also increased in demented patients with probable AD.

Aged↗

PubMed2002

Multi-male mating, probability of conception, and litter size in the prairie vole (Microtus ochrogaster).

We conducted a mating experiment in the laboratory using prairie voles, Microtus ochrogaster, to document that multi-male mating (MMM) can occur in this supposedly monogamous species and to test two hypotheses for the advantages of MMM in female mammals. The two hypotheses are that MMM (1) increases the probability of pregnancy and (2) increases litter size. We also tested the hypothesis that multiple copulations, rather than multiple partners, increases litter size and/or probability of pregnancy. Females were given a choice of mating with any of three males, each of which was tethered in a separate compartment. The mate choice bouts were recorded on videotape. We recorded the number of copulations and number of males with which females mated over a 24 h period. Litter size and probability of pregnancy were not significantly different for females that mated with one, two or three males. Increasing numbers of copulations, independent from the number of males, also did not increase litter size but did significantly increase the probability of pregnancy. MMM, at least in prairie voles, must serve some function other than increasing litter size and probability of conception.

Journal Article↗

PubMedDate not supplied

The albedo effect on neutron transmission probability.

The aim of this study is to evaluate the albedo effect on the neutron transmission probability through slab shields. For this reason we have considered an infinite homogeneous slab having a fixed thickness equal to 20 lambda (lambda is the mean free path of the neutron in the slab). This slab is characterized by the factor Ps (scattering probability) and contains a vacuum channel which is formed by two horizontal parts and an inclined one (David, M. C. (1962) Duc and Voids in shields. In Reactor Handbook, Vol. III, Part B, p. 166). The thickness of the vacuum channel is taken equal to 2 lambda. An infinite plane source of neutrons is placed on the first of the slab (left face) and detectors, having windows equal to 2 lambda, are placed on the second face of the slab (right face). Neutron histories are sampled by the Monte Carlo method (Booth, T. E. and Hendricks, J. S. (1994) Nuclear Technology 5) using exponential biasing in order to increase the Monte Carlo calculation efficiency (Levitt, L. B. (1968) Nuclear Science and Engineering 31, 500-504; Jehouani, A., Ghassoun, J. and Abouker, A. (1994) In Proceedings of the 6th International Symposium on Radiation Physics, Rabat, Morocco) and we have applied the statistical weight method which supposes that the neutron is born at the source with a unit statistical weight and after each collision this weight is corrected. For different values of the scattering probability and for different slopes of the inclined part of the channel we have calculated the neutron transmission probability for different positions of the detectors versus the albedo at the vacuum channel-medium interface. Some analytical representations are also presented for these transmission probabilities.

Monte Carlo Method↗

PubMed2000

Calculation of emission probabilities of X-rays and Auger electrons emitted in radioactive disintegration processes

A complete set of data for the decay scheme of a radionuclide requires knowledge of the emission probabilities of X-rays and Auger electrons. If adopted sets of transition probabilities for the transitions of the decay scheme and atomic shell data (such as fluorescence yields and relative emission probabilities) are available, the emission probabilities of the X-rays and Auger electrons can be calculated from these data. Only data calculated in this way are consistent with the adopted input data and can be compared with measured data. Conclusions can be drawn with respect to the internal consistency of the data sets by comparing the measured and calculated data. Hence, the EMISSION program has been developed and tested to calculate X-ray and Auger electron emission probabilities along with their error propagation.

Journal Article↗

PubMed2002

The probability that similar haplotypes are identical by descent.

The logic of gene mapping in highly penetrant diseases is to find the minimal overlap of haplotypes that are identical by descent (IBD). If the pedigree is unknown, identity by descent of haplotype overlap cannot be established with certainty. In many cases, it is intuitively clear that similar haplotypes are indeed IBD. The logical and statistical evaluation of haplotype overlap requires that probabilities of IBD are substantial. It is, therefore, important to estimate these probabilities. In this paper, we derive a recursive formula for the probability of IBD. Simulations are used to validate the expected values and to study the variability around the expected value. We demonstrate that for populations 1000 generations of age - without bottlenecks - haplotypes of 1 cM consisting of at least five microsatellite markers have a significant probability to be IBD. Likewise, SNP haplotypes of 1 cM should consist of at least nine identical SNP alleles for a similar probability of IBD. Without considering bottlenecks, haplotypes consisting of as few as three SNPs spanning a region of less than 0.01 cM are likely IBD in populations that are 10000 generations of age.

Chromosome Mapping↗

PubMed1992

Why people with probable minor psychiatric morbidity consult a doctor.

This epidemiological investigation examines factors determining medical consultation in people with probable minor psychiatric morbidity. About 54% of people with probable minor psychiatric morbidity and about 23% of the (numerically much greater) remainder with lower probability of psychiatric morbidity consulted a doctor, usually a primary care physician, in the two weeks prior to a research interview. Medical consultation rates were higher in females than in males. The dominant finding was that in people with probable minor psychiatric morbidity physical illness was strongly associated with medical consultation. Almost 89% of males and 97% of females with probable minor psychiatric morbidity and physical illness consulted a doctor in the two weeks prior to interview. Logistic regression modelling was used to investigate the joint effects on medical consultation of physical illness and six socio-demographic variables, and physical illness emerged as the major single determinant of medical consultation in women and, in men, it exerted its effect through an interaction with lower educational level.

Adolescent↗

PubMed1998

Children's construction of fair chances: adjusting probabilities.

A probability-adjustment task was presented to 6-14-year-old children. In 2 experiments, children had to generate equal probabilities by completing the missing beads in a target urn with 1 type of beads presented beside a full urn with both winning and losing beads. The task was embedded in a competitive game. This relevant-involvement method secured optimal understanding and motivation. The analysis was based on number of matches with, and sum of distances from, the correct response and the predictions of other strategies. The results indicate that only at around the age of 13 did most children proportionally integrate the 2 dimensions (i.e., the numbers of winning and losing beads). The youngest sometimes relied on 1 dimension, and 9- and 10-year-olds partly combined the 2 types of quantities additively. The cognition involved in probability adjustment was analytic rather than global or intuitive. The ability to generate equal probabilities is discussed in terms of the many faces of probability.

Adolescent↗

PubMed2006

Target location probability effects in visual search: an effect of sequential dependencies.

Target location probability was manipulated in a visual search task. When the target was twice as likely to appear on 1 side of the display as the other, manual button-press response times were faster (Experiment 1A) and first saccades were more frequently directed (Experiment 1B) to the more probable locations. When the target appeared with equal probability at each location in this search task, performance benefited from repetition of target location in the preceding trials (Experiment 2). When the trial sequence was constrained so that target location did not repeat within a series of 4 trials, there was no longer an advantage for more probable locations (Experiment 3). The authors conclude that the search benefits for more probable locations resulted from short-term target location repetitions.

Adolescent↗

PubMed2004

The emerging lexicon of children with phonological delays: phonotactic constraints and probability in acquisition.

The effects of phonotactic constraints (i.e., the status of a sound as correctly or incorrectly articulated) and phonotactic probability (i.e., the likelihood of a sound sequence) on lexical acquisition have been investigated independently. This study investigated the interactive influence of phonotactic constraints and phonotactic probability on lexical acquisition in 3 groups of children: children with functional phonological delays (PD), phonology-matched, younger, typically developing children (PM), and age-/vocabulary-matched typically developing peers (AVM). Sixty-eight children participated in a multitrial word-learning task involving nonwords varying in phonotactic constraints (IN vs. OUT) and phonotactic probability (common vs. rare). Correct and error responses were analyzed. Results indicated that OUT sound sequences were learned more rapidly than IN sound sequences. This suggests that OUT sounds may be salient because they represent only a small subset of the child's sound system. The effect of phonotactic probability varied across groups: Children with PD showed a common sound sequence disadvantage, younger PM children showed a common sound sequence advantage, and AVM children showed no effect. Moreover, error analyses indicated that children with PD had particular difficulty creating lexical representations and associations between lexical and semantic representations when learning common sound sequences. Children with PD may rely more heavily on lexical representations to learn new words or may have difficulty learning common sound sequences because of the high degree of similarity between these sequences and other known words. Finally, the effect of phonotactic probability was consistent across IN and OUT sound sequences, suggesting that the lexical representation of both correctly articulated and misarticulated words is based on the adult-target pronunciation.

Articulation Disorders↗

PubMed2003

Eye movements reveal the on-line computation of lexical probabilities during reading.

Skilled readers are able to derive meaning from a stream of visual input with remarkable efficiency. In this article, we present the first evidence that statistical information latent in the linguistic environment can contribute to an account of reading behavior. In two eye-tracking studies, we demonstrate that the transitional probabilities between words have a measurable influence on fixation durations, and using a simple Bayesian statistical model, we show that lexical probabilities derived by combining transitional probability with the prior probability of a word's occurrence provide the most parsimonious account of the eye movement data. We suggest that the brain is able to draw upon statistical information in order to rapidly estimate the lexical probabilities of upcoming words: a computationally inexpensive mechanism that may underlie proficient reading.

Bayes Theorem↗

PubMed2002

Probability of assertive behaviour, interpersonal anxiety and self-efficacy of South African registered dietitians.

OBJECTIVES: There is little information on the probability of assertive behaviour, interpersonal anxiety and self-efficacy in the literature regarding dietitians. The objective of this study was to establish baseline information of these attributes and the factors affecting them. METHOD: Questionnaires collecting biographical information and self-assessment psychometric scales measuring levels of probability of assertiveness, interpersonal anxiety and self-efficacy were mailed to 350 subjects, who comprised a random sample of dietitians registered with the Health Professions Council of South Africa. RESULTS: Forty-one per cent (n=145) of the sample responded. Self-assessment inventory results were compared to test levels of probability of assertive behaviour, interpersonal anxiety and self-efficacy. The inventory results were compared with the biographical findings to establish statistical relationships between the variables. The hypotheses were formulated before data collection. CONCLUSION: Dietitians had acceptable levels of probability of assertive behaviour and interpersonal anxiety. The probability of assertive behaviour was significantly lower than the level noted in the literature and was negatively related to interpersonal anxiety and positively related to self-efficacy.

Adult↗

PubMed2004

Factors affecting the probability of first year medical student dropout in the UK: a logistic analysis for the intake cohorts of 1980-92.

BACKGROUND: In the context of the 1997 Report of the Medical Workforce Standing Advisory Committee, it is important that we develop an understanding of the factors influencing medical school retention rates. AIMS: To analyse the determinants of the probability that an individual medical student will drop out of medical school during their first year of study. METHOD: Binomial and multinomial logistic regression analysis of individual-level administrative data on 51 810 students in 21 medical schools in the UK for the intake cohorts of 1980-92 was performed. RESULTS: The overall average first year dropout rate over the period 1980-92 was calculated to be 3.8%. We found that the probability that a student would drop out of medical school during their first year of study was influenced significantly by both the subjects studied at A-level and by the scores achieved. For example, achieving 1 grade higher in biology, chemistry or physics reduced the dropout probability by 0.38% points, equivalent to a fall of 10%. We also found that males were about 8% more likely to drop out than females. The medical school attended also had a significant effect on the estimated dropout probability. Indicators of both the social class and the previous school background of the student were largely insignificant. CONCLUSIONS: Policies aimed at increasing the size of the medical student intake in the UK and of widening access to students from non-traditional backgrounds should be informed by evidence that student dropout probabilities are sensitive to measures of A-level attainment, such as subject studied and scores achieved. If traditional entry requirements or standards are relaxed, then this is likely to have detrimental effects on medical schools' retention rates unless accompanied by appropriate measures such as focussed student support.

Adult↗

PubMedDate not supplied

Paternity probabilities of biologic fathers and unexcluded, falsely accused men using blood group markers.

A frequent legal argument raised in defense of men accused of paternity, but not excluded by genetic tests, is that the probabilities of paternity of falsely accused men are similar to those of biologic fathers. This assertion was tested in a computer simulation experiment that used a database of 15,000 actual paternity cases to provide red cell and HLA phenotypes of mothers, children, and putative fathers. Tests had a combined probability of exclusion of 97.3 percent. Equal numbers of true and false fathers were generated from the data by computer to achieve a prior probability of paternity of 0.5. True fathers' phenotypes were those of unexcluded men from actual cases (Group A) or of mothers from actual cases (Group B) in which paternity was not excluded. The false father group was created by assigning the phenotypes of racially identical men who were selected at random from among cases other than their own. Probabilities of paternity were calculated for the men in each group and were classified into descriptive intervals. The frequency of men in each group was compared in each interval. The frequency distributions of probabilities of paternity for true fathers and unexcluded, falsely accused men (false fathers) were markedly dissimilar.

Computer Simulation↗

PubMed2003

Probability of anti-D development in D- patients receiving D+ RBCs.

BACKGROUND: In some situations, the administration of D+ RBCs to D- patients is necessary. The probability of a subsequent anti-D formation is assumed to be around 80 percent, a figure based primarily on studies in healthy volunteers. It was hypothesized that patients requiring blood transfusion have a much lower probability of developing antibodies. STUDY DESIGN AND METHODS: A retrospective analysis was performed whereby 78 D- patients were evaluated for the development of RBC antibodies after administration of D+ RBCs. For the analysis of the cross-sectional observations, parametric models were used for interval-censored data. RESULTS: Anti-D was detected in 16 of 78 patients. Considering the individual patient's inspection times, the calculated probability of developing antibody following D+ RBC supply was shown to be below 41.7 percent (upper 95% confidence bound) and estimated as 30.4 percent. The data hinted toward an inverse correlation between the number of transfused units and the probability of antibody formation. Interestingly, 6 of these 16 patients developed additional IgG autoantibody. In 3 of those cases, evidence for prolonged hemolysis was found. CONCLUSION: The actual frequency of antibody formation in our patients is much lower than assumed. On the other hand, prolonged hemolysis probably induced by additional autoreactive antibodies might occur. This possible complication has not yet been addressed. Further studies might reveal whether a less restricted transfusion policy with respect to D matching is justified in selected patients.

Adult↗

PubMed2005

A novel KCNJ11 mutation associated with congenital hyperinsulinism reduces the intrinsic open probability of beta-cell ATP-sensitive potassium channels.

The beta-cell ATP-sensitive potassium (KATP) channel controls insulin secretion by linking glucose metabolism to membrane excitability. Loss of KATP channel function due to mutations in ABCC8 or KCNJ11, genes that encode the sulfonylurea receptor 1 or the inward rectifier Kir6.2 subunit of the channel, is a major cause of congenital hyperinsulinism. Here, we report identification of a novel KCNJ11 mutation associated with the disease that renders a missense mutation, F55L, in the Kir6.2 protein. Mutant channels reconstituted in COS cells exhibited a wild-type-like surface expression level and normal sensitivity to ATP, MgADP, and diazoxide. However, the intrinsic open probability of the mutant channel was greatly reduced, by approximately 10-fold. This low open probability defect could be reversed by application of phosphatidylinositol 4,5-bisphosphates or oleoyl-CoA to the cytoplasmic face of the channel, indicating that reduced channel response to membrane phospholipids and/or long chain acyl-CoAs underlies the low intrinsic open probability in the mutant. Our findings reveal a novel molecular mechanism for loss of KATP channel function and congenital hyperinsulinism and support the importance of phospholipids and/or long chain acyl-CoAs in setting the physiological activity of beta-cell KATP channels. The F55L mutation is located in the slide helix of Kir6.2. Several permanent neonatal diabetes-associated mutations found in the same structure have the opposite effect of increasing intrinsic channel open probability. Our results also highlight the critical role of the Kir6.2 slide helix in determining the intrinsic open probability of KATP channels.

Animals↗

PubMed2005

Probability models to facilitate a declaration of pest-free status, with special reference to tsetse (Diptera: Glossinidae).

A methodology is presented to facilitate a declaration that an area is 'pest-free' following an eradication campaign against an insect pest. This involves probability models to assess null trapping results and also growth models to help verify, following a waiting period, that pests were not present when control was stopped. Two probability models are developed to calculate the probability of negative trapping results if in fact insects were present. If this probability is sufficiently low, then the hypothesis that insects are present is rejected. The models depend on knowledge of the efficiency and the area of attractiveness of the traps. To verify the results of the probability model, a waiting period is required to see if a rebound occurs. If an incipient but non-detectable population remains after control measures are discontinued, then a rebound should occur. Using a growth model, the rate of increase of an insect population is examined starting from one gravid female or one male and a female. An example is given for tsetse in which both means and confidence limits are calculated for a period of 24 reproductive periods after control is terminated. If no rebound is detected, then a declaration of eradication can be made.

Animals↗

PubMed2005

Estimating the probability of the public perceiving a decrease in atmospheric haze.

Regional haze regulations require progress toward reducing atmospheric haze as measured by particle scattering coefficient of visible light. From a practical perspective, this raises the following question: Given a decrease in extinction, what is the probability that people will notice an improvement in visibility? This paper proposes a quantitative definition of the probability of a perceptible increase in visibility given a decrease in light extinction and a general method to estimate this probability from perception measurements made in the field under realistic conditions. Using data from a recent study of visibility perception by 8 observers, it is estimated that a 2-4 deciview change gives a 67% maximum probability of detecting the improvement. Stated another way, the odds of seeing a difference are at most 2:1 for a change of 2-4 deciviews. A 90% probability requires a change of at least 3.5-7.0 deciviews. The limitations and possible bias in the results of this study are discussed. These results may have a major effect on the cost-benefit analysis of regulatory actions to improve visibility.

Air↗