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PubMed2005

Quantitative analysis of group-specific brain tissue probability map for schizophrenic patients.

We developed group-specific tissue probability map (TPM) for gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF) on the common spatial coordinates of an averaged brain atlas derived from normal controls (NC) and from schizophrenic patients (SZ). To identify differences in group-specific TPMs, we used quantitative evaluation methods based on differences in probabilistic distribution as a global criterion, and the mean probability and the similarity index (SI) by lobe as regional criteria. The SZ group showed more spatial variation with a lower mean probability than NC subjects. And, for the right temporal and left parietal lobes, the SI between each group was lower than the other lobes. It can be said that there were significant differences in spatial distribution between controls and schizophrenic patients at those areas. In case of female group, although group differences in the volumes of GM and WM were not significant, global difference in the probabilistic distribution of GM was more prominent and the SI was lower and its descent rate was greater in all lobes, compared with the male group. If these morphological differences caused by disease or group-specific features were not considered in TPM, the accuracy and certainty of specific group studies would be greatly reduced. Therefore, suitable TPM is required as a common framework for functional neuroimaging studies and an a priori knowledge of tissue classification.

Adult↗

PubMed2005

Application of probability circles analysis to the construction of calibration curves for infra red spectroscopy.

A new method, based on the presentation of initial data in the form of probability circles (PC), has been developed for constructing a calibration curve, which shows a monotonic dependence with respect to the given concentration. The centre of the reference probability circle is defined by its mean value and the radius of the circle is calculated as the value of the standard deviation of the sampling considered. The comparative probability circle is defined by the same corresponding parameters but rotated, relative to the initial reference circle, by an angle, which is related to the Pearson's correlation coefficient (PCC). The two parameters of the PCC and the statistical proximity factor (PCF), which defines the positions of the centres of the circles relative to each other, can be chosen as statistical parameters for the construction of the desired calibration curve. Experiments realized with the mixture of two liquids (chloroform serves as the basic matrix) and acetone (serves as an additive) confirm the efficiency of this new analytical method and demonstrate a possible increase sensitivity for the detection of lower concentration limit by approximately one order of magnitude. This new approach, which is free from model assumptions, and having very clear geometrical meaning, can be applied for different types of spectra and has many potential applications in the construction of calibration curves for different additives embedded within different matrices.

Calibration↗

PubMed2003

Hypothesis generation, probability judgment, and individual differences in working memory capacity.

This research examined the role of working memory (WM) in probability judgment and hypothesis generation using a simulated task that involved estimating the likelihood that particular menu items would be ordered by customers at a dinner. Five main findings were observed. First, judgments of the likelihood of individual items were made relative to alternatives retrieved from long-term memory. Second, the number of alternatives retrieved was positively correlated with a measure of WM-capacity (the operation-span task). Third, participants' probability judgments were subadditive (summing to well over 100%). Fourth, the degree to which participants' judgments were subadditive was affected by the number and strength of the alternatives retrieved from long-term memory. Fifth, the degree to which participants were subadditive was negatively correlated with WM-capacity. The results suggest that individual differences in WM-capacity are fundamental to hypothesis generation and probability judgment.

Humans↗

PubMed2000

Selective responsiveness of medial prefrontal cortex neurons to the meaningful stimulus with a low probability of occurrence in rats.

Multi-unit neuronal activity was recorded in the medial prefrontal cortex (mPFC) of 13 chronically prepared male rats while they performed a two-tone discrimination task. Tones at 1000 and 2000 Hz were sequentially presented at intervals of 3-6 s. The duration of each tone was 0.8 s. Rats were trained to press a bar within 1.2 s after the cessation of the 1000 Hz tone (target), and not to press the bar when the other tone (non-target) was presented. Intracranial electrical stimulation (ICS) of the medial forebrain bundle was given as a reward immediately after the rats had correctly responded to the target tone. Probability of the target occurrence was either 30% or 70% in different sessions. When the target tone was presented on only 30% of the trials, the mPFC neurons in the majority of rats tested (10/13) exhibited phasic excitation about 100 ms after the onset of the target tone. However, when the target tone occurred on 70% of the trials, mPFC neurons in most of rats (11/13) did not show excitatory responses, and in some of them (5/13) were inhibited. No mPFC neurons exhibited significant responses to the non-target tone, regardless of its probability. These results suggest that the mPFC neurons selectively respond to meaningful events with a low probability of occurrence.

Acoustic Stimulation↗

PubMed2003

An evidential support accumulation model of subjective probability.

A model of cue-based probability judgment is developed within the framework of support theory. Cue diagnosticity is evaluated from experience as represented by error-free frequency counts. When presented with a pattern of cues, the diagnostic implications of each cue are assessed independently and then summed to arrive at an assessment of the support for a hypothesis, with greater weight placed on present than on absent cues. The model can also accommodate adjustment of support in light of the baserate or prior probability of a hypothesis. Support for alternatives packed together in a "residual" hypothesis is discounted; fewer cues are consulted in assessing support for alternatives as support for the focal hypothesis increases. Results of fitting this and several alternative models to data from four new multiple-cue probability learning experiments are reported.

Cues↗

PubMed1985

Factors affecting the probability of conception after treatment of subfertile men with varicocele by transcatheter embolization with Bucrylate.

Retrospective analysis of 100 patients treated for varicocele-associated infertility by means of transcatheter embolization with 2-isobutyl-cyano acrylate (Bucrylate, Ethicon Inc., Somerville, NJ) reveals that the age of the man and the duration of infertility do not influence the probability of pregnancy after treatment. Patients treated for subclinical varicoceles had the same probability of success as patients with larger varicoceles. The following factors were found to have predictive power as far as the posttreatment success rate is concerned: the coincidence of other disease interfering with the fertility of the man or woman, serum follicle-stimulating hormone concentration, total testicular volume, and pretreatment semen quality. Depending on the latter factors, the probability of conception varies between 8% and 80%. It seems possible to define certain subgroups of varicocele patients with poor, moderate, or good fertility prognosis.

Bucrylate↗

PubMed1983

Energetics of DNA twisting. I. Relation between twist and cyclization probability.

The twisting potential of DNA has been determined directly by a method that measures the cyclization probability or j-factor of EcoRI restriction fragments as a function of DNA twist. The cyclization probability is proportional to Kc, the equilibrium constant for cyclization of the restriction fragment via its cohesive ends (Shore et al., 1981). Here we vary the twist of the DNA by making small internal additions to or deletions from a 242 bp EcoRI restriction fragment. A series of 12 DNA molecules has been studied, which range in length from 237 to 254 bp. The cyclization probability is measured from the rates of covalent closure by phage T4 DNA ligase of two systems: (1) a linear restriction fragment in equilibrium with its cyclized form and (2) half molecules (cut by a blunt-end endonuclease) in equilibrium with joined half molecules. The striking result is that, in this DNA size range, the j-factor depends strongly on the fractional twist: the difference between the total helical twist and the nearest integer. Thus j depends in an oscillatory manner on DNA length between 237 and 254 bp with a period of about 10 bp. These data give the free energy of DNA twisting as a function of twist. The curve of j versus DNA length can be fitted to a harmonic twisting potential with a torsional constant of C = 2.4 X 10(-19) erg cm. This value is in reasonable agreement with different estimates of C made by Barkley & Zimm (1979: C = 1.8 X 10(-19) to 4.1 X 10(-19) erg cm) and is somewhat larger than the value obtained resulting from the kinetics of DNA twisting measured by fluorescence depolarization of ethidium intercalated into DNA (C = 1.4 X 10(-19) erg cm; Millar et al., 1982; Thomas et al., 1980) or from spin label studies (Hurley et al., 1982). Our experiments provide a direct measurement of the torsional free energy and they show that the DNA twisting potential is symmetric. Our experiments also indicate that the DNA helix is continuous, or nearly so, in a nicked circle; presumably this happens because the DNA stacking interaction maintains the double helix in register across a single-strand nick. As a consequence, the twist of a singly nicked DNA circle is integral for small (approximately equal to 250 bp) planar DNA circles and there is a change in twist upon cyclization.(ABSTRACT TRUNCATED AT 400 WORDS)

Autoradiography↗

PubMed1987

How probable are antibody cross-reactions?

Antibodies to polypeptides are increasingly being used in research. Their specificity and tight but reversible binding make them ideal for applications such as identification of proteins, immunological quantification or purification, and peptide mapping. Antibodies are also used in medicine to deliver loads to specific sites in tissues, and in electron microscopy as heavy metal conjugates to locate antigens in thin sections. While these techniques depend on specificity of antibody binding, it is occasionally observed that cross-reactions occur. These cross-reactions are attributed to the existence of one or more antibody binding sites common to both polypeptides. It is important to know whether these cross-reactions are expected due to chance alone, or if they are improbable and likely due to some causative agent. Examples of such causative agents might include gene duplication events or convergence due to functional constraints. At the present time, good methods for predicting the probability and therefore the frequency of cross-reactions are unavailable. In this paper we apply some recently reported mathematical results to address the following questions: (1) What is the probability that polyclonal or monoclonal antibodies raised against a given polypeptide will cross-react with another polypeptide due to chance alone? (2) What is the probability that polyclonal or monoclonal antibodies raised against a given polypeptide will cross-react with one or more polypeptides in a pool of polypeptides? Approximate answers to these questions are presented for cases where amino acid compositions of linear polypeptides are known or unknown, but the amino acid sequence of one or more of the polypeptides is not known. Implications of the results for antibody use in protein research are discussed.

Amino Acid Sequence↗

PubMed1983

Predicting the probability of bone metastasis through histological grading of prostate carcinoma: a retrospective correlative analysis of 81 autopsy cases with antemortem transurethral resection specimen.

In a retrospective correlative analysis of postmortem findings and antemortem transurethral resection specimens from 81 patients with prostatic carcinoma a simple and reliable prediction index was found. This index was derived from the transurethral resection specimen in regard to the probability of ultimate bone metastasis by tumor and was obtained by dividing the number of prostatic tissue chips involved with tumor by the total number of prostatic tissue chips examined microscopically. We found that when 75 per cent or more of the transurethral resection chips were involved with tumor, regardless of the degree of tumor differentiation, the probability of bone metastasis was more than 9.0 (greater than 90 per cent), whereas the probability was 0.58 for 50 to 75 per cent involvement, 0.38 for 30 to 50 per cent involvement, 0.27 for 20 to 30 per cent involvement, 0.10 for 10 to 20 per cent involvement and 0.06 for less than 10 per cent involvement. Other tumor grading systems, such as the Gleason system, also were compared. A good correlation was obtained by the Gleason grading system in the prediction of bone metastasis but the system is not as simple or as reproducible as the tumor involvement index described herein. Other parameters, such as prostatic acid phosphatase and prostatic specific antigen as determined by the immunoperoxidase method, had no specific or significant value in the prediction of bone metastasis. Our findings reaffirm the relatively old concept that the extensiveness of tumor involvement in the transurethral resection specimen is the single most important factor in the prediction of the clinical behavior of the prostatic carcinoma.

Acid Phosphatase↗

PubMed2000

Probability summation for multiple patches of luminance modulation.

When components of a compound pattern stimulate different visual mechanisms, psychophysical performance typically improves by a small amount consistent with probability summation amongst independent detectors. Here we extend previous summation experiments by (i) plotting full psychometric functions; and (ii) using compound stimuli with components that varied in up to three stimulus dimensions: spatial frequency (1, 4, 5 or 11 c/deg), orientation (0 degrees, +/-45 degrees ), and position. Stimulus components were isolated circular sine-phase patches of grating centred on up to four corners of an imaginary square surrounding a fixation-point. Combinations of component patches produced compound stimuli made from up to 16 components that differed in various combinations of the three stimulus dimensions. Other than when the spatial frequency was 11 c/deg, results were well described using: (i) probabilistic summation of individual psychometric functions; (ii) the Quick pooling formula; and (iii) the signal detection analysis for 2IFC developed by Tyler and Chen (2000) [Signal detection theory in the 2AFC paradigm: attention, channel uncertainty and probability summation (under review)]. We conclude that in general, nonlinear spatial summation is consistent with probabilistic summation across independent detecting mechanisms that vary in spatial frequency (a range of at least 1-5 c/deg), orientation (a range of 90 degrees ) and position (a range of at least 24 cycles at 4 c/deg). In further experiments, results were found to be consistent with probability summation for pairs of orthogonally oriented step-edge stimuli and a matrix of randomly oriented 11 c/deg sine-wave patches. This casts doubt on the generality of a recent suggestion that local interactions between colinearly oriented detectors within a spatial neighbourhood of around four cycles may contribute to nonlinear spatial summation [Bonneh & Sagi, 1998; Vision Research, 38, 3541-3553].

Contrast Sensitivity↗

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↗

PubMedDate not supplied

Probability of monozygotic twinning as a reflection of the genetic control of cell development.

The stability of the incidence of monozygotic twinning (MZT) suggests that its origin is genetically, rather than environmentally, controlled. Available data, though scant, supports our hypothesis that the MZT probability is (1/2)K, where K is a species-specific integer parameter. For humans MZT occurs in about four of 1000 births, which is close to one occurrence in 2(8) births, i.e. K = 8. The environmental factors are not the cause of MZT, but may influence its expression. When this influence is in effect under some extreme experimental conditions the above form of MZT probability is observed. Binary structure of the MZT probability provides insight into genetic control mechanism of cell division.

Cell Division↗

PubMed2002

Substratification of stage T1C prostate cancer based on the probability of biochemical recurrence.

OBJECTIVES: To evaluate the influence of preoperative prostate-specific antigen (PSA), biopsy Gleason sum, and prostate biopsy quantitative histologic findings on the probability of biochemical failure in an attempt to identify criteria to substratify Stage T1c prostate cancer more accurately. METHODS: We reviewed the records of 1149 patients who underwent prostatectomy for T1c disease between 1988 and 2000. Biochemical recurrence (PSA 0.2 ng/mL or greater) defined the endpoint in this study. Recursive partitioning analysis was used to establish cutpoints for preoperative PSA level, biopsy Gleason sum, number of positive biopsy cores, and maximal percentage of any single biopsy core involved with cancer. These cutoff values were then evaluated using Kaplan-Meier estimations to determine the probability of remaining biochemically recurrence free. RESULTS: Using a PSA cutpoint of 10 ng/mL or a biopsy Gleason sum of 7, two groups of patients were identified (T1cI and T1cII). The rate of freedom from PSA recurrence at 3, 5, and 10 years after surgery for T1cI was 98%, 96%, and 96%, respectively, and for T1cII was 86%, 83%, and 73%, respectively (P <0.001). For T1cII patients, the greatest percentage of cancer in a single biopsy core was found to be a predictor of biochemical failure on multivariate analysis and, using a cutoff value of 50%, further stratified the PSA recurrence-free rates for the men in group T1cII (90% and 85% versus 75% and 56% at 5 and 10 years after surgery, respectively, P = 0.03). CONCLUSIONS: The results of this study demonstrate that within Stage T1c there are two populations of patients with significantly different recurrence probabilities: T1cI (Gleason sum less than 7 and PSA 10 ng/mL or less) and T1cII (Gleason sum 7 or greater or PSA greater than 10 ng/mL). Furthermore, using a cutpoint of 50% of cancer in a single core of biopsy tissue, additional risk stratification is afforded to men with higher risk "T1cII" cancer.

Aged↗

PubMed2000

The influence of luting cement on the probabilities of survival and modes of failure of cast full-coverage crowns.

OBJECTIVES: This study compares the probabilities of survival and modes of failure of cast full-coverage crowns bonded with five cements when subjected to tensile pull-off testing. METHODS: Five groups of 25 sound human premolar teeth were prepared for full-coverage crowns, impressions recorded and customized castings fabricated in Ni-Cr-Mb bonding alloy. The cements tested were zinc phosphate, a hand-mixed and capsulated conventional glass-ionomer cement, a resin-modified glass-ionomer cement and a resin composite luting cement. The cemented crowns were stored in water at 37 degrees C for 24 h prior to application of a tensile pull-off force at a strain rate of 10 mm/min. The loads at failure were ranked and modelled by derived Weibull functions each describing the probability of a given specimen failing under a given load. Non-parametric statistical analysis was also applied to the results. RESULTS: There were no significant differences between the loads at failure of zinc phosphate cement, the hand-mixed or the capsulated glass-ionomer cements. The resin-modified glass-ionomer cement and the resin composite cement failed at significantly higher loads than the other three cements, but were not significantly different from each other. The Weibull modulus ranking for each cement from highest to lowest was resin composite = zinc phosphate, resin-modified glass-ionomer, hand-mixed conventional glass-ionomer and capsulated conventional glass-ionomer cement. SIGNIFICANCE: Weibull analysis allows dentists to compare the probability of survival of a crown bonded with different cements at a chosen load giving an indication of cement reliability.

Adhesiveness↗

PubMed1999

The re-incarnation, re-interpretation and re-demise of the transition probability model.

There are two classes of models for the cell cycle that have both a deterministic and a stochastic part; they are the transition probability (TP) models and sloppy size control (SSC) models. The hallmark of the basic TP model are two graphs: the alpha and beta plots. The former is the semi-logarithmic plot of the percentage of cell divisions yet to occur, this results in a horizontal line segment at 100% corresponding to the deterministic phase and a straight line sloping tail corresponding to the stochastic part. The beta plot concerns the differences of the age-at-division of sisters (the beta curve) and gives a straight line parallel to the tail of the alpha curve. For the SC models the deterministic part is the time needed for the cell to accumulate a critical amount of some substance(s). The variable part differs in the various variants of the general model, but they do not give alpha and beta curves with linear tails as postulated by the TP model. This paper argues against TP and for an elaboration of SSC type of model. The main argument against TP is that it assumes that the probability of the transition from the stochastic phase is time invariant even though it is certain that the cells are growing and metabolizing throughout the cell cycle; a fact that should make the transition probability be variable. The SSC models presume that cell division is triggered by the cell's success in growing and not simply the result of elapsed time. The extended model proposed here to accommodate the predictions of the SSC to the straight tailed parts of the alpha and beta plots depends on the existence of a few percent of the cell in a growing culture that are not growing normally, these are growing much slower or are temporarily quiescent. The bulk of the cells, however, grow nearly exponentially. Evidence for a slow growing component comes from experimental analyses of population size distributions for a variety of cell types by the Collins-Richmond technique. These subpopulations existence is consistent with the new concept that there are a large class of rapidly reversible mutations occurring in many organisms and at many loci serving a large range of purposes to enable the cell to survive environmental challenges. These mutations yield special subpopulations of cells within a population. The reversible mutational changes, relevant to the elaboration of SSC models, produce slow-growing cells that are either very large or very small in size; these later revert to normal growth and division. The subpopulations, however, distort the population distribution in such a way as to fit better the exponential tails of the alpha and beta curves of the TP model.

Animals↗

PubMed1999

What price information? Modelling threshold probabilities of fetal loss.

This paper is an extension of previous work in which an alternative method of measuring the benefits of antenatal screening was proposed. The method is based on the elicitation of threshold probabilities of fetal loss at which women would be indifferent between having and not having an amniocentesis for the prenatal diagnosis of fetal abnormalities. The aim of this paper is to extend the previous work by modelling the preferences of a larger sample of women and investigating the consistency and validity of their responses. The threshold probabilities are elicited using standard gambles and modelled using Tobit estimation. The results indicate that it is possible to model these probabilities in this way and that it is possible to obtain a high degree of consistency in response to standard gamble questions. While establishing the validity of the responses is more difficult there is some evidence that the technique can provide valid responses.

Adult↗

PubMed1998

[Preoperative coronarography in heart valve disease patients. A probability analysis of coronary lesion].

INTRODUCTION AND OBJECTIVES: The indication of preoperative coronary angiography is routinely performed for patients who are going to valve replacement surgery. The need of coronary angiography is based on age, gender and previous angina, but it is not usually based on risk factors. The purpose of this study has been to find markers to predict the probability of coronary lesion in this group of patients. PATIENTS AND METHODS: We studied retrospectively a population of 541 patients with valvular heart disease who underwent preoperative coronary angiography from 1989 to 1994. Mean age was 61.8 (range 34-82). There were 301 men and 240 women. We analyzed in each patient different variables such as age, gender, previous angina, hypertension, diabetes mellitus, tobacco and familial predisposition. We correlated these variables with the presence of coronary lesion by multivariate analysis. RESULTS: There were 73 patients with coronary lesion greater than 50%. The prevalence of significant coronary artery disease was 13.4%. Angina was present in 34.6%. The risk of coronary lesion was defined as odds ratio: previous angina 3.3; tobacco 2.6; diabetes 2.2; hypertension 1.8 and age 1.4. The others variables were not predictor of coronary lesion. The probability of coronary lesion in patients without those variables (angina, tobacco, diabetes, hypertension) was 4%. If we analyzed age, the probability of coronary lesion was 3% in patients under 65 years and 6% above 65 years. CONCLUSIONS: The lack of previous angina and at least the three risk factors described as predictors of coronary lesion (hypertension, tobacco and diabetes) can define a group of patients with a very low prevalence of coronary lesion, especially if they are under 65 years. It can allow us to avoid preoperatory coronary angiography in patients who undergo valve replacement.

Adult↗

PubMed2001

Stress testing for risk stratification of patients with low to moderate probability of acute cardiac ischemia.

In summary, this article focused on the use of stress testing to risk-stratify patients at the conclusion of their emergency evaluation for ACI. As discussed, those patients in the probably not ACI category require additional risk stratification prior to discharge. It should be kept in mind that patients in this category are heterogeneous, containing subgroups at both higher and lower risk of ACI and cardiac events. The patients with lower pretest probability for ACI may only need exercise testing in the ED. Patients with higher pretest probability should undergo myocardial perfusion or echocardiographic stress testing to maximize diagnostic and prognostic information. Prognostic information is the key to provocative testing in the ED. Prognostic information is the component that will help emergency physicians identify the patients who may be discharged home safely without having to worry about a 6% annual cardiac death rate and a 10% overall death rate over the next 30 months. Stress testing provides this key prognostic data, and it can be obtained in short-stay chest pain observation units in a safe, timely, and cost-effective fashion.

Acute Disease↗