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PubMed2005

Aging and conditional probability judgments: a global matching approach.

Age differences in bias in conditional probability judgments were investigated based on predictions derived from the Minerva-Decision Making model (M. R. P. Dougherty, C. F. Gettys, & E. E. Ogden, 1999), a global matching model of likelihood judgment. In this study, 248 younger and older adults completed frequency judgment and conditional probability judgment tasks. Age differences in the frequency judgment task are interpreted as an age-related deficit in memory encoding. Older adults' stronger biases in the probability judgment task point to age differences in criterion setting. Age-related biases were eliminated when age groups were equated on memory encoding by means of study time manipulation. The authors conclude that older adults' stronger judgment biases are a function of memory impairment.

Adolescent↗

PubMed1989

Probability matching in visual selective attention.

Jonides (1980, p. 111) suggested a model to account for shifts of spatial attention in visual search tasks with less than 100% cue validity. This two-stage probability matching model was subsequently tested by Jonides (1983). Reaction time distribution characteristics indeed provided some support for the model. In the present paper the relevant data presented in Jonides (1980, 1981, 1983) are further analysed. The results of this analysis strongly support the probability matching hypothesis. Probability matching is apparently a very important strategic characteristic of visual spatial attention that deserves much more study.

Attention↗

PubMed2002

Probability matching: encouraging optimal responding in humans.

Two hundred undergraduate students participated in a repeated-trials binary choice procedure in which choice of one outcome was correct on 75% of trials. Subjects received 192 trials and were divided into five conditions: (1) control; (2) subjects were given the actual probabilities; (3) subjects were told if they did well they could leave early; (4) competition condition; (5) midway through the task subjects were asked to recommend a strategy for another subject. Half of the subjects in each group were told that the best they could do was to be correct on 75% of the trials. This manipulation permitted assessment of the hypothesis that subjects in probability-matching tasks are seeking a strategy that will be correct on 100% of the trials. The results partially confirmed this hypothesis. In addition, two of the variables improved performance significantly (giving probabilities and asking subjects to recommend a strategy). However, while subjects in all groups improved significantly over trials, optimal choice did not occur in this task.

Adult↗

PubMed1995

Nonindependence of matches at different loci in DNA profiles: quantifying the effect of close relatives on the match probability.

In comparing a particular DNA profile with that from an unknown (but distinct) individual, matches at different loci between the profiles will not be independent, even in a randomly mating population, because of the presence in the population of relatives of the individuals. The paper contains a theoretical analysis of the extent of this effect on the match probability, for profiling techniques which separately probe different loci. Naive calculation using the product rule could substantially understate the match probability. Past a certain point, the testing of additional loci provides no more information than would be available in discriminating between sibs. The correlation effect described here would be unimportant in criminal casework if close relatives of the suspect, and in particular full-sibs, were excluded as possible culprits. In the absence of such exclusions the current practice of effectively ignoring such relatives in presenting match probabilities could be extremely prejudicial to a suspect, even in cases in which there is no direct evidence to incriminate his/her relatives.

Alleles↗

PubMed2003

Learning new words II: Phonotactic probability in verb learning.

Phonotactic probability, a measure of the likelihood of occurrence of a sound sequence, appears to facilitate noun learning (H. L. Storkel, 2001). Nouns and verbs, however, tend to differ in rate of acquisition, indicating that word-learning mechanisms may differ across grammatical class. The purpose of the current study was to examine the effect of phonotactic probability on verb learning. Thirty-four typically developing preschool children participated in a multitrial word-learning task involving nonwords varying in phonotactic probability paired with unfamiliar actions. Multiple measures of word learning were obtained at increasing numbers of exposures. Correct responses were analyzed to examine rate of word learning. Results paralleled those of the previous noun-learning study, with common sound sequences being learned more rapidly than rare sound sequences. The results are interpreted in relation to the effect of distributional regularities on acquisition and the reported discrepancy between noun and verb learning in English.

Analysis of Variance↗

PubMed2002

Diagnostic value of d-dimer in patients with a moderate pretest probability of deep venous thrombosis.

The negative predictive value (NPV) of d-dimer (DD) for the exclusion of venous thromboembolism is, overall, high and tends to increase as clinical pretest probability decreases. We have assessed the accuracy of a diagnostic protocol including clinical evaluation and DD in 134 outpatients presenting with a moderate pretest probability of proximal deep venous thrombosis (DVT). In these patients, a negative DD value safely excluded DVT (NPV 100%, 95% CI 85-100) In our experience, these results are equivalent to those found for low-pretest probability patients and therefore the same diagnostic strategy can be used for both risk groups.

Aged↗

PubMed1996

The probabilities of supercoil removal and decatenation by yeast DNA topoisomerase II.

BACKGROUND: In yeast a single type II DNA topoisomerase is involved in both the removal of DNA supercoils and the unlinking of intertwined pairs of newly replicated chromosomes or plasmids; in bacteria, two type II enzymes, DNA gyrase and DNA topoisomerase IV, function separately in the passage of DNA segments in cis and in trans. To deduce the molecular characteristics of these enzyme-mediated reactions, the efficiencies of supercoil removal and decatenation by the yeast enzyme upon the addition of a nonhydrolysable ATP analogue were determined. RESULTS: The probability that a bound enzyme transports a DNA segment in cis increases with positive or negative supercoiling of the DNA, and transport is nearly quantitative at high degrees of supercoiling. The relative probabilities of transporting a contiguous and noncontiguous DNA segment by a yeast enzyme bound to one member of a singly linked pair of 3.6-kb rings were calculated from the observed efficiency of decatenation. When the enzyme-bound ring is highly supercoiled, transport of a noncontiguous segment is more probable than a contiguous one. CONCLUSION: A DNA-bound yeast enzyme has no intrinsic bias in its selection of a contiguous or noncontiguous DNA segment for transport, and the selection is determined by DNA conformations. For the singly linked dimeric catenane studied, a high degree of supercoiling of the enzyme-bound DNA does not make supercoil removal more favourable than decatenation. In the case of bacterial gyrase, however, wrapping of a DNA segment around the enzyme is expected to strongly favour the transport of a contiguous segment.

Biological Transport, Active↗

PubMed1989

Paternity testing with an absent mother. The probability of exclusion of red cell surface antigen, Gm, Hp, and HLA systems in North American whites and blacks.

Blood tests in cases of disputed paternity can be extremely useful even when the mother's blood sample is not available. The mean probability of exclusion (A) of red cell surface antigen, Gm, Hp, and HLA systems was determined in this situation for North American whites and blacks by creating pairs of a man and an unrelated child. In whites, the most valuable of the systems investigated to indicate nonpaternity for false fathers were HLA, Rh, Fy, and MNSs, in that order. HLA, MNSs, and Gm were the most valuable systems in blacks. With all of the genetic systems used in this study, the combined probability of exclusion (CPE) of men falsely accused of paternity, in cases where the mother is absent, is approximately 95 percent for whites and 92 percent for blacks. Since only indirect exclusions are possible without the mother, the common test panel of HLA and red cell antigens may not always allow an adequate study. Extended testing is recommended to include additional genetic systems in order to achieve an average combined probability of exclusion of at least 95 percent.

Black People↗

PubMedDate not supplied

Validating the probability of paternity.

In cases of disputed parentage, it is commonly thought that the probability of paternity (P) represents the probability that the tested man is the biologic father of the child whose parentage is in doubt and that the paternity index (PI) is the likelihood ratio that enters into this probability. Using the results of HLA typing in a sample of disputed parentage cases, the distribution of P was examined within two groups: actual mother-alleged father-child trios, and simulated mother-unrelated man-child trios. These distributions were found to be roughly consistent with the usual understanding of P.

Female↗

PubMed2003

The utility of pretest probability assessment in patients with clinically suspected venous thromboembolism.

The assessment of pretest probability (PTP), with stratification into low-, intermediate- and high-risk groups is an essential initial step in the current diagnostic management of patients with suspected venous thromboembolism (VTE). In combination with additional information, it reduces the need for initial and supplementary imaging, and allows considerable refinement of the posterior probability of VTE following non-invasive imaging. PTP may be assessed either empirically or by using various decision rules or scoring systems, the best known of which are the simplified Wells scores for suspected deep vein thrombosis (DVT) and pulmonary embolism (PE), and the Geneva score for suspected PE. Each of these approaches shows similar directional and categorical accuracy, and has been validated as facilitating clinically useful classification of the PTP, although an overview of data suggests that fewer patients tend to be classified as low PTP when assessed empirically. This group is the most important to identify, as several outcome studies have shown that imaging and treatment are safely obviated in outpatients with suspected DVT or PE who have a low PTP in combination with negative d-dimer testing, a subgroup accounting for up to half of all patients studied. Hence, while probably not of critical importance, the explicit approach offered by scoring systems might be preferred over empirical assessment, particularly when used by more junior staff.

Bayes Theorem↗

PubMed1991

[Prognostic factors in Crohn's disease. Is the probability of a later operation assessable at the initial diagnosis?].

Data were retrospectively analysed of 492 patients (268 women, 224 men; mean age 27 [9-71] years) to find out what features present at time of first diagnosis (age, sex, site of disease, biochemical findings) will play a role in determining the probability of surgery ultimately becoming necessary. The probability of an operation ten years after first diagnosis was 55%, after 20 years it was 88%, significantly higher if the ileum rather than only the colon was affected. Age and sex had no influence. Patients with a haemoglobin content below 12 g/dl (women) or below 13.5 g/dl (men), or an albumin concentration under 4.0 g/dl, or a blood sedimentation rate over 30 mm in the first hour had a probability of operation after ten years nearly three times higher than those without one of these findings. A prognosis about the likely future course of the disease can be made from its localization and the biochemical values. Thus patients with an early ileocolitis and unfavourable biochemical findings apparently constitute a subgroup in which the disease takes a primarily aggressive course.

Age Factors↗

PubMed1984

Care of patients with a low probability of acute myocardial infarction. Cost effectiveness of alternatives to coronary-care-unit admission.

We conducted a cost-effectiveness analysis to examine the clinical and economic consequences of alternatives to admission to a coronary-care unit for patients who have a relatively low probability of acute myocardial infarction. Despite the fact that all our assumptions were slanted to favor the current standard policy of admission to a coronary-care unit, our analysis shows that admission to an intermediate-care unit providing resuscitative facilities and prophylactic lidocaine is highly cost effective. For patients with about a 5 per cent probability of infarction, admission to a coronary-care unit would cost $2.04 million per life saved and $139,000 per year of life saved, as compared with intermediate care. For the expected number of such patients annually in the United States, the cost would be $297 million to save 145 lives. At probabilities of infarction up to about 20 per cent, the incremental cost to save a year of life by choosing a coronary-care unit over an intermediate-care unit would be higher than the estimated cost of saving a year of life by treating a 40-year-old man with mild hypertension. Our results suggest that many patients who have a low risk of acute myocardial infarction would be appropriate candidates for admission to an intermediate-care unit.

Ambulatory Care↗

PubMed1998

Objective estimates of the probability of death from burn injuries.

BACKGROUND: Over the past 20 years, there has been remarkable improvement in the chances of survival of patients treated in burn centers. A simple, accurate system for objectively estimating the probability of death would be useful in counseling patients and making medical decisions. METHODS: We conducted a retrospective review of all 1665 patients with acute burn injuries admitted from 1990 to 1994 to Massachusetts General Hospital and the Shriners Burns Institute in Boston. Using logistic-regression analysis, we developed probability estimates for the prediction of mortality based on a minimal set of well-defined variables. The resulting mortality formula was used to determine whether changes in mortality have occurred since 1984, and it was tested prospectively on all 530 patients with acute burn injuries admitted in 1995 or 1996. RESULTS: Of the 1665 patients (mean [+/-SD] age, 21+/-20 years; mean burn size, 14+/-20 percent of body-surface area), 1598 (96 percent) lived to discharge. The mean length of stay was 21+/-29 days. Three risk factors for death were identified: age greater than 60 years, more than 40 percent of body-surface area burned, and inhalation injury. The mortality formula we developed predicts 0.3 percent, 3 percent, 33 percent, or approximately 90 percent mortality, depending on whether zero, one, two, or three risk factors are present. The results of the prospective test of the formula were similar. A large increase in the proportion of patients who chose not to be resuscitated complicated comparisons of mortality over time. CONCLUSIONS: The probability of mortality after burns is low and can be predicted soon after injury on the basis of simple, objective clinical criteria.

Adolescent↗

PubMed2005

Probability current in protein electron transfer reactions: a Green function pathway model.

In a biological electron transfer reaction problem we have found distinct electron probability current representations of macromolecular currents, amino acid and interamino acid currents, atomic and interatomic currents. We present a general interatomic current approach to obtain the electron probability current from donor to acceptor sites, and vice versa. Symmetric (or antisymmetric) renormalizable interatomic currents provide exact (or approximate) effective tunneling matrix element between donor and acceptor states. The electron probability currents allow us to investigate stationary tunneling pathways through protein bridge medium, from molecular to subatomic resolution at any level of electronic description of the biological structure. Analytical comparison among interatomic pathway models is presented and we found equivalent interatomic current representations with distinct dependence on the tunneling energy from the weak to strong coupling between protein bridge and the donoracceptor sites.

Electron Transport↗

PubMed2000

Estimating the probability for a protein to have a new fold: A statistical computational model.

Structural genomics aims to solve a large number of protein structures that represent the protein space. Currently an exhaustive solution for all structures seems prohibitively expensive, so the challenge is to define a relatively small set of proteins with new, currently unknown folds. This paper presents a method that assigns each protein with a probability of having an unsolved fold. The method makes extensive use of protomap, a sequence-based classification, and scop, a structure-based classification. According to protomap, the protein space encodes the relationship among proteins as a graph whose vertices correspond to 13,354 clusters of proteins. A representative fold for a cluster with at least one solved protein is determined after superposition of all scop (release 1.37) folds onto protomap clusters. Distances within the protomap graph are computed from each representative fold to the neighboring folds. The distribution of these distances is used to create a statistical model for distances among those folds that are already known and those that have yet to be discovered. The distribution of distances for solved/unsolved proteins is significantly different. This difference makes it possible to use Bayes' rule to derive a statistical estimate that any protein has a yet undetermined fold. Proteins that score the highest probability to represent a new fold constitute the target list for structural determination. Our predicted probabilities for unsolved proteins correlate very well with the proportion of new folds among recently solved structures (new scop 1.39 records) that are disjoint from our original training set.

Amino Acid Sequence↗

PubMed1974

Probability of gene fixation in an expanding finite population.

A mathematical theory was developed, based on diffusion models, that enables us to compute the probability of a rare mutant allele eventually spreading through a population when the population size changes with time. In particular, we elaborated the case in which the mutant allele has a definite selective advantage and the population expands following the logistic law. In this case, the probability of ultimate fixation of a single mutant is given by u = 2s(Z/N), where s is the selective advantage and Z/N is a factor by which the probability of fixation is modified through population expansion. Analytical expression was obtained for Z/N, and the validity of the formula for u was checked by Monte Carlo experiments.

Alleles↗

PubMed2001

The effects of event rate and signal probability on children's vigilance.

Using the study of vigilance in adults as their model, the researchers examined task parameters and their interactions in a study of sustained attention in children from a non-clinical population. Two levels of event rate (low and high) were combined with two levels of signal probability (low and high) in 14-minute vigilance tasks in which children viewed small and large squares presented successively on a computer screen. Seven- and eight-year-old children were instructed to press a button whenever a small square appeared. Signal detection analyses were employed, as well as the traditional measures identifying hits, false alarms, and reaction time. The results support the traditional findings in adult tasks: participants performed most accurately and quickly in the high event rate and high probability condition; low probability elicited a more conservative decision-making criterion, a standard characterized by less willingness to risk false alarms; such conservatism increased over the periods of watch; and the vigilance decrement emerged over time. However, the finding that the high event rate condition improved perceptual sensitivity reversed the event rate effect consistently reported in the adult literature. The above findings are discussed in light of both research and clinical implications.

Age Factors↗

PubMed2005

Spatial summation in the tactile sensory system: probability summation and neural integration.

Psychophysical thresholds for the detection of a 300-Hz burst of vibration applied to the thenar eminence were measured for stimuli applied to the skin through 1.5 cm2 and through 0.05 cm2 contactors. Thresholds were approximately 13 dB lower when the area of the contactor was 1.5 cm2 than when it was 0.05 cm2. The difference between the thresholds measured with the large and small contactors was significantly reduced when only the lowest thresholds obtained in the testing sessions were considered. This result supports the hypothesis that one component of spatial summation in the P channel is probability summation. In addition, threshold measurements within a session were less variable when measured with the 1.5 cm2 contactor. We conclude that spatial summation in the P channel is a joint function of two processes that occur as the areal extent of the stimulus increases: probability summation in which the probability of exceeding the psychophysical detection threshold increases as the number of receptors of varying sensitivities increases, and neural integration in which neural activity originating from separate receptors is combined within the central nervous system rendering the channel more sensitive to the stimulus.

Adult↗