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PubMed1997

Work-up of patients with malignancy after an intermediate-probability ventilation-perfusion scan: why don't physicians pursue a definitive diagnosis?

RATIONALE AND OBJECTIVES: The authors determined whether there are specific patient characteristics associated with the clinical decision to eschew further diagnostic testing in patients in whom a ventilation-perfusion (V-P) scan indicates intermediate probability of pulmonary embolism (PE). MATERIALS AND METHODS: The authors reviewed all intermediate-probability V-P scans obtained in a 12-month period. Patients were divided into two groups. Group 1 comprised patients in whom a definitive diagnosis of PE was not obtained and who were not treated for PE (n = 57); group 2 comprised patients in whom the diagnosis of PE was confirmed or excluded and who, if PE was confirmed, received appropriate treatment (n = 14). Age, gender, frequency of malignancy, and survival of patients in groups 1 and 2 were compared. RESULTS: The frequency of malignancy was significantly greater in group 1 than in group 2 (P = .012). Although the estimated 2-year survival of group 1 patients was significantly less than that of group 2 patients (P = .039), this difference is likely due to confounding by age and malignancy. CONCLUSION: When an intermediate-probability V-P scan is obtained, physicians are significantly less likely to pursue a definitive diagnosis of PE in patients with malignancy.

Aged↗

PubMed2002

[Probabilities of controlling tumors and complications (TCP/NTCP) after radiotherapy: methodologic, physical, and biological aspects].

Radiotherapy is aimed at getting the best possible therapeutic ratio (tumor local control versus morbidity). Physicists and radiation oncologists have to evaluate explicitly or implicitly the probability of induced complications to normal surrounding tissues. This is based on published data and clinician's experience. Quantitative methods have been introduced with different models in order to predict the impact of partial or global irradiation on a normal organ. These models correspond to the Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP). These biological models may be useful to evaluate the quality of a treatment planning or for the optimization process. The methodologies used and the clinical data are developed and discussed.

Dose-Response Relationship, Radiation↗

PubMed2003

Count data, detection probabilities, and the demography, dynamics, distribution, and decline of amphibians.

The evidence for amphibian population declines is based on count data that were not adjusted for detection probabilities. Such data are not reliable even when collected using standard methods. The formula C = Np (where C is a count, N the true parameter value, and p is a detection probability) relates count data to demography, population size, or distributions. With unadjusted count data, one assumes a linear relationship between C and N and that p is constant. These assumptions are unlikely to be met in studies of amphibian populations. Amphibian population data should be based on methods that account for detection probabilities.

Amphibians↗

PubMed2001

Difficulties in parentage analysis: the probability that an offspring and parent have the same heterozygous genotype.

Parentage studies often estimate the number of parents contributing to half-sib progeny arrays by counting the number of alleles attributed to unshared parents. This approach is compromised when an offspring has the same heterozygous genotype as the shared parent, for then the contribution of the unshared parent cannot be unambiguously deduced. To determine how often such cases occur, formulae for co-dominant markers with n alleles are derived here for Ph, the probability that a given heterozygous parent has an offspring with the same heterozygous genotype, and Pa, the probability that a randomly chosen offspring has the same heterozygous genotype as the shared parent. These formulae have been derived assuming Mendelian segregation with either (1) an arbitrary mating system, (2) random mating or (3) mixed mating. The maximum value of Pa under random mating is 0.25 and occurs with any two alleles each at a frequency of 0.5. The behaviour with partial selfing (where reproduction is by selfing with probability s, and random mating otherwise) is more complex. For n < or = 3 alleles, the maximum value of Pa occurs with any two alleles each at a frequency of 0.5 if s < 0.25, and with three equally frequent alleles otherwise. Numerically, the maximum value of Pa for n > or = 4 alleles occurs with n* < or = n alleles at equal frequencies, where the maximizing number of alleles n* is an increasing function of the selfing rate. Analytically, the maximum occurs with all n alleles present and equally frequent if s > or = 2/3. In addition, the potential applicability of these formulae for evolutionary studies is briefly discussed.

Alleles↗

PubMed1998

The effects of mating probability on the population genetics of nematodes.

We review how constraints on the mating probability of female worms by segregation within individual host guts form a critical element in the parasite population structure of nematodes. We consider the effects of these constraints on the population genetics of nematodes under various assumptions regarding worm competition as reflected in the relationship between the abundance of a certain genotype within the gut and the probability of reproductive success. The consequences for the emergence of resistance to drugs and immunotherapy and implications for host-parasite coevolution are discussed. We also review evidence for genetic heterogeneity in parasite populations as a necessary prerequisite for the applicability of mating probability models designed to assess the population genetics of nematodes.

Animals↗

PubMed1981

Antibodies to Eubacterium and Peptostreptococcus species and the estimated probability of Crohn's disease.

Anaerobic coccoid rods belonging to species of Eubacterium and Peptostreptococcus agglutinate more frequently with sera from patients with Crohn's disease than with sera from patients suffering from other diseases and from healthy subjects. Results of agglutination test with four strains of coccoid anaerobes were used to estimate the probability that a patient suffers from Crohn's disease. The data on healthy subjects and patients with Crohn's disease were subjected to logistic discriminant analysis. With the methods and interpretation described, 52% of the patients with Crohn's disease were recognized as 'definite' or 'probable' Crohn's disease and 14% as 'suspected'. Only 1% of the healthy subjects were classified as 'suspected' and non as 'definite' or 'probable' Crohn's disease.

Adolescent↗

PubMed1987

Most probable numbers of organisms: revised tables for the multiple tube method.

Estimation of numbers of organisms is often made using dilution series, for example when examining water samples for coliform organisms. In this paper the most probable numbers (MPNs) are calculated for a 15-tube series consisting of five replicates at three consecutive tenfold dilutions. Exact conditional probabilities are computed to replace previous approximations. When growth is observed in several of the tubes it is not realistic to select a single MPN. Instead a most probable range (MPR) should be reported. But using an MPR creates problems when comparison has to be made with a legislated, single-valued Standard. It is suggested that the wording of the Standards should be expressed differently when the multiple tube method is used.

Bacteria↗

PubMed1993

Relative probability of mutagenic translesion synthesis on the leading and lagging strands during replication of UV-irradiated DNA in a human cell extract.

We have previously demonstrated mutagenic bypass of pyrimidine dimers during SV40 origin-dependent replication of UV-irradiated DNA in human cell extracts [Thomas, D. C., & Kunkel, T. A. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 7744-7748]. Here we use two vectors having the origin of replication on opposite sides of a lacZ alpha reporter gene to examine the relative probability of mutagenic translesion synthesis on the leading and lagging strands. Although replication of both vectors is inhibited by UVB irradiation in a dose-dependent manner, the covalently closed DNA products of replication contain T4 endonuclease sensitive sites, indicating that bypass of cyclobutane pyrimidine dimers occurred. At fluences of 70 and 100 J/m2, the mutant frequencies obtained with both vectors are substantially higher than with control DNAs. Sequence analysis of mutants obtained with both vectors reveal three types of mutations at frequencies significantly above those obtained from replication of undamaged DNA. These are C-->T transitions, accounting for about two-thirds of the mutants, a small number of CC-->TT substitutions, and complex mutations. Comparing the distribution of C-->T substitutions in the two spectra permits an estimation of the probability of mutagenic translesion replication of the same sequence when replicated as the leading or lagging strand. The data suggest that the overall average UV-independent C-->T substitution probability per phenotypically detectable dipyrimidine site is the same during leading and lagging strand replication. However, statistically significant differences are observed when the distribution of C-->T substitutions is considered.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗

PubMed2001

Probability of acceptable intubation conditions with low dose rocuronium during light sevoflurane anaesthesia in children.

BACKGROUND: To define the rocuronium doses which would provide 50%, 90%, and 95% probability of 'acceptable' intubation conditions during light sevoflurane anaesthesia, we studied 60 children aged 2-7 years in a prospective, randomised, assessor blinded study. METHODS: After mask ventilation with 1 MAC sevoflurane/N2O for 17+/-1 (x+/-SD) min we administered rocuronium (either 0.15, 0.22, 0.3, 0.5, or 1.0 mg. kg(-1)) or placebo, and quantified the evoked force of the adductor pollicis muscle. Intubation conditions were assessed before and 2 min after injection of the test drug. RESULTS: Intubation conditions were improved significantly with rocuronium and scored 'acceptable' in 70%, 90%, and 100% of the children after injection of rocuronium 0.15, 0.22, and 0.3 mg x kg(-1), respectively. In parallel, twitch tension decreased to 53% (6-100), 26% (11-100), and 11% (0-19) of baseline (median (range)). Recovery of train-of-four ratio to 0.8 was achieved 13 (7-19), 16 (8-28), and 27 (23-44) min after injection of the respective rocuronium doses. Higher rocuronium doses did not further improve intubation conditions but only prolonged time of neuromuscular recovery. Logistic regression analysis revealed that rocuronium 0.11 (CI 0.05-0.16), 0.21 (0.14-0.28), and 0.25 (0.15-0.34) mg x kg(-1) provides a 50%, 90%, and 95% probability of 'acceptable' intubation conditions in children during 1 MAC sevoflurane/N2O anaesthesia, respectively. Furthermore, we calculated that force depression of adductor pollicis muscle to 81% (CI 72-90), 58% (42-74), and 50% (29-71) of baseline is associated with 50%, 90%, and 95% probability of 'acceptable' intubation conditions. CONCLUSIONS: Submaximal depression of muscle force with low dose rocuronium improves intubation conditions in children during light sevoflurane anaesthesia while allowing rapid recovery of neuromuscular function. However, when using low dose rocuronium neuromuscular monitoring may be helpful to detect children with inadequate response to the relaxant so as to avoid an unsuccessful intubation attempt.

Androstanols↗

PubMed1992

Cognitive-experiential self-theory and subjective probability: further evidence for two conceptual systems.

Three experiments (N = 1,331) demonstrated that research findings on suspiciousness about coincidences (Miller, Turnbull, & McFarland, 1989) can be accounted for in terms of subjective probability, as predicted by cognitive-experiential self-theory (CEST) but in contrast with the norm theory (NT) account offered by Miller et al. (1989). Ss participated in a hypothetical (Experiments 1 and 2) or real (Experiment 3) lottery game in which they chose between 2 bowls offering equivalent probabilities of winning or losing but differing with respect to absolute numbers (e.g., 1 in 10 vs. 10 in 100). Responses across 4 conditions (2 probability levels x 2 outcome types) and across the 3 experiments supported predictions derived from CEST but not those derived from NT. Results are discussed in terms of 2 conceptual systems, rational and experiential, that operate by different rules of inference.

Adult↗

PubMed2000

A sampling approach to biases in conditional probability judgments: beyond base rate neglect and statistical format.

Conditional probability judgments of rare events are often inflated. Early accounts assumed a general deficit in using statistical base rates. More recent approaches predict improvement when problems are presented in frequency format or refer to natural categories. The present theory focuses on sampling processes. Experiment 1 showed that a seeming advantage of frequency over probability formats is due to a confounded factor, the need to mentally transform stimulus samples. An information search paradigm was used in Experiment 2. When sampling by the predictor, the probability to be estimated, p(criterion/predictor), was conserved in the samples and judgments were quite accurate. However, when sampling by the criterion, the low base-rate event was strongly overrepresented, accounting for the entire bias. Judgments were quite sensitive to the sampled data, but failed to take sampling constraints into account, as shown in Experiments 3 and 4.

Adult↗

PubMed2000

Probability judgment in three-category classification learning.

People give subadditive probability judgments--in violation of probability theory--when asked to assess each in a set of 3 or more mutually exclusive hypotheses, as indicated by their sum exceeding 1. Three potential evidential influences on subadditivity--cue conflict, cue frequency, and cue redundancy--are distinguished and tested in 5 experiments using a classification-learning task. Results indicate that (a) judgments of probability and of frequency are systematically subadditive even when the judgments are based on cues learned within the experimental context, (b) cue conflict has a reliable influence on the degree of subadditivity, and (c) judgments in this context are well described by a linear-discounting model within the framework of support theory.

Concept Formation↗

PubMed2002

Preparatory processes in the task-switching paradigm: evidence from the use of probability cues.

The purpose of the investigations was to dissociate processes of task preparation from task execution in the task-switching paradigm. The basic assumption was that task repetitions have 2 advantages over task shifts: an activation advantage as a result of the execution of the same task type in the pretrial, and an expectation advantage, because participants, in general, implicitly expect a repetition. In Experiments 1-3, the authors explicitly manipulated expectancies by presenting cues that announced a shift and/or a repetition with probabilities of 1.00, .75, .50, or .25. Increasing latencies with decreasing probability for shifts and repetitions show that the expectation advantage can be equalized by preparation. However, the activation advantage represented by constant shift costs between tasks of the same probability is not penetrable by preparation. In Experiments 4 and 5, the authors found evidence that preparation involves activation of the expected task and inhibition of distracting tasks.

Adaptation, Psychological↗

PubMed2007

Conditional probability versus spatial contiguity in causal learning: Preschoolers use new contingency evidence to overcome prior spatial assumptions.

This study examines preschoolers' causal assumptions about spatial contiguity and how these assumptions interact with new evidence in the form of conditional probabilities. Preschoolers saw a toy that activated in the presence of certain objects. Children were shown evidence for the toy's activation rule in the form of patterns of probability: The toy was more likely to activate either when objects made contact with its surface (on condition) or when objects were several inches above its surface (over condition). In Experiment 1, 61 three-year-olds saw a deterministic activation rule. In Experiments 2 and 3, 48 four-year-olds saw an activation rule that was probabilistic. In Experiment 4, 30 four-year-olds saw a screening-off pattern of activation. In all 4 experiments, children used new evidence in the form of patterns of probability to make accurate causal inferences, even in the face of conflicting prior beliefs about spatial contiguity. However, children were more likely to make correct inferences when causes were spatially contiguous, particularly when faced with ambiguous evidence.

Association Learning↗

PubMed1989

Quantitative meanings of verbal probability expressions.

The meanings of 18 verbal probability expressions were studied in 3 ways: (a) frequency distributions of what single number best represented each expression; (b) word-to-number acceptability functions from what range of numbers from 0% to 100% best represented each expression; and (c) number-to-word acceptability functions from which expressions were appropriate for multiples of 5% from 5% to 95%. These results agreed highly with others and were highly consistent across methods. Expressions incorporating the stem probable were quantitatively synonymous with expressions incorporating the stem likely. Except for expressions using the word chance, positive expressions (e.g., likely) were closer to 50% in meaning than corresponding negative expressions (e.g., unlikely). This method proved very useful in deriving fuzzy-set membership functions for probability words, encouraging us in our ongoing codification effort.

Adult↗

PubMed1992

Probability effects on stimulus evaluation and response processes.

This study investigated the effects of probability information on response preparation and stimulus evaluation. Eight subjects responded with one hand to the target letter H and with the other to the target letter S. The target letter was surrounded by noise letters that were either the same as or different from the target letter. In 2 conditions, the targets were preceded by a warning stimulus unrelated to the target letter. In 2 other conditions, a warning letter predicted that the same letter or the opposite letter would appear as the imperative stimulus with .80 probability. Correct reaction times were faster and error rates were lower when imperative stimuli confirmed the predictions of the warning stimulus. Probability information affected (a) the preparation of motor responses during the foreperiod, (b) the development of expectancies for a particular target letter, and (c) a process sensitive to the identities of letter stimuli but not to their locations.

Attention↗

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↗

PubMed2006

The influence of improper sets of information on judgment: how irrelevant information can bias judged probability.

This article introduces 2 new sources of bias in probability judgment, discrimination failure and inhibition failure, which are conceptualized as arising from an interaction between error prone memory processes and a support theory like comparison process. Both sources of bias stem from the influence of irrelevant information on participants' probability judgments, but they postulate different mechanisms for how irrelevant information affects judgment. The authors used an adaptation of the proactive interference (PI) and release from PI paradigm to test the effect of irrelevant information on judgment. The results of 2 experiments support the discrimination failure account of the effect of PI on probability judgment. In addition, the authors show that 2 commonly used measures of judgment accuracy, absolute and relative accuracy, can be dissociated. The results have broad implications for theories of judgment.

Analysis of Variance↗