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PubMedDate not supplied

Generalization of map estimation in SAAM II: validation against ADAPT II in a glucose model case study.

Bayesian approaches to model identification [e.g., maximum a posteriori (MAP) estimation] are receiving increasing attention in metabolism since important quantitative knowledge has become available in the last decades, e.g., from tracer experiments. By suitably exploiting this knowledge, more complex physiological models than those solely based on experimental data (Fisherian approach) become resolvable. While ADAPT II is the reference software for MAP estimation in pharmacokinetic/pharmacodynamic/metabolic system analysis, another popular, user-friendly and state-of-the-art software is SAAM II. However, SAAM II does not handle a priori information on correlation among parameters, thus allowing a limited version of MAP estimation to be performed. The aim here is twofold. First, we show that this limitation of SAAM II can be easily overcome by resorting to a probability theory result. Second, we test SAAM II vs ADAPT II implementation of MAP estimation in a real case study: the Bayesian identification of a recently proposed two-compartment minimal model of glucose kinetics during an intravenous glucose tolerance test. SAAM II MAP estimates of glucose effectiveness (SG) and insulin sensitivity (S(I)) obtained in a group of 22 healthy humans are in excellent agreement with those of ADAPT II: S(G) = 2.84 +/- 0.27 vs. 2.84 +/- 0.27 (mlmin(-1) kg(-1), mean +/- SD) and S(I) = 11.46 +/- 1.69 vs. 11.47 +/- 1.69 [10(-2) ml kg(-1) min(-1)/ (microU ml(-1))]. The SAAM II vs. ADAPT II estimates are virtually identical (P > 0.44 and 0.68 for S(G) and S(I), respectively) and also closely correlated (p = 0.9998 and 0.9999).

Algorithms↗
PubMed1999

Unconditional security of quantum key distribution over arbitrarily long distances

Quantum key distribution is widely thought to offer unconditional security in communication between two users. Unfortunately, a widely accepted proof of its security in the presence of source, device, and channel noises has been missing. This long-standing problem is solved here by showing that, given fault-tolerant quantum computers, quantum key distribution over an arbitrarily long distance of a realistic noisy channel can be made unconditionally secure. The proof is reduced from a noisy quantum scheme to a noiseless quantum scheme and then from a noiseless quantum scheme to a noiseless classical scheme, which can then be tackled by classical probability theory.

Journal Article↗
PubMed1996

Learning multiple causes by competition enhanced least mean square error reconstruction.

In this paper we studied a self-organization principle that input should be best reconstructed from a factorial distributed hidden representation, which has been addressed in the literature recently. An auto-encoder network is trained by the Least Mean Square Error Reconstruction (LMSER) while the redundance in the representation is reduced by a proposed anti-Hebbian scheme, in which a penalty term called Receptive Field Overlapping Index (RFOI) is combined into the objective function for enhancing competition among nodes in the network. Our learning scheme provides a way for balancing the cooperation and competition necessary for the self-organization process thus realizes the multiple causes model, which accounts for an observed data by combining assertions from the discovered causes or features in the data. Our experiment results demonstrate again the powerful information processing capability inherent to the popular weighted sum followed by sigmoid squashing. Comparing with previous probability theory based multiple causes models, our scheme is much easier to implement and quite reliable.

Algorithms↗
PubMed2002

Strategies and statistics of sampling for rare individuals.

Diverse subdisciplines within entomology recognize the detection of rare individuals as the precursor to effective management of these individuals. Unfortunately, detection methods have often developed on a case-by-case basis, and advances in one subdiscipline have not carried over to similarly related fields. The biology of a particular organism will certainly affect sampling methods, but the underlying principles governing the power of a sampling strategy to detect rare individuals will apply across taxa. Our review of the sampling literature demonstrates the common problem of detecting rare individuals, reviews the fundamentals of probability theory as a foundation for any monitoring program, and discusses the inferences that can be drawn from samples, especially when resources limit sampling efforts. Particular emphasis is placed on binomial-, beta-binomial-, and hypergeometric-based sampling strategies as they pertain to quarantine inspections for exotic pests, veterinary/medical entomology, and insecticide resistance monitoring.

Animals↗
PubMed1999

Causal interactions, fuzzy sets and cerebrovascular 'accident': the limits of evidence-based medicine and the advent of complexity-based medicine.

In evidence-based medicine, stroke subtype is diagnosed after a sequential search for etiology; the first positive test result of significant severity rounds off to one overwhelming cause. Degree of severity, interaction among variables, and concomitant variable conditions are not considered in defining the cause of stroke. Yet, thrombus formation, and possibly vascular rupture, is an interactive process involving the vascular wall, flow properties of the blood and blood constituents; this process occurs in homeostasis and pathology. Evidence-based medicine ignores this process and instead studies stroke using crisp 'all or none' classification where subtypes are distinct and interactively relate only to outcome. As a result, scientific inquiry is focused on prediction for the collective of patients. The statistical approach of evidence-based medicine is founded on probability theory, itself rooted in classical set theory where elementhood is all (1) or none (0), and opposites interact only to form the null set. Fuzzy set theory, where set membership is to degree [0, 1], encompasses classical set theory, allows for an interactive process between variables, and therefore becomes the measure of complexity. Fuzzy set theory can change the scientific method of evidence-based medicine.

Cerebrovascular Disorders↗
PubMedDate not supplied

Predictive value of sequential testing in screening for silent myocardial ischemia in asymptomatic middle-aged men (the ECCIS Project).

The accuracy of sequential testing in the noninvasive diagnosis of coronary artery disease has been established in the symptomatic clinical populations, while little is known about its value when applied to low prevalence groups, such as totally asymptomatic men. To evaluate the accuracy of noninvasive sequential testing in the diagnosis of silent myocardial ischemia, data were collected from exercise electrocardiogram, 201Tl perfusion scintigraphy and radionuclide angiography for 62 totally asymptomatic middle-aged men who underwent coronary arteriography because they were positive for two or more markers of myocardial ischemia as determined by a diagnostic screening of a nonbiased population consisting of 4,842 presumably healthy men aged 40-59 years (the ECCIS Project). The predictive value of serial testing procedures for significant coronary artery obstruction was 35%. Predictive values of an abnormal electrocardiogram associated with either an abnormal 201Tl scintigram, an abnormal isotopic ventriculography, or both were 33, 38 and 31%, respectively. In asymptomatic middle-aged men, there is at least a 50% likelihood that an abnormal radionuclide test is a false-positive result, and the positive predictive value is not enhanced by the concordance of an abnormal 201Tl scintigraphy with an abnormal isotopic ventriculography. Thus, the application of noninvasive sequential testing in screening for asymptomatic coronary artery disease is limited by its low predictive value in accordance with the Bayesian probability theory.

Adult↗
PubMed1993

Accuracy of exercise 201Tl myocardial scintigraphy in asymptomatic young men.

BACKGROUND: Little is known about the diagnostic usefulness of 201Tl scintigraphy for detecting asymptomatic coronary artery disease in apparently healthy men. We thus evaluated planar 201Tl exercise myocardial scintigraphy in 845 asymptomatic male military aircrew undergoing coronary arteriography because of abnormal noninvasive tests suggesting possible myocardial ischemia. METHODS AND RESULTS: Patients were stratified by prior disease risk into six subgroups using age (< 45 and > or = 45 years) and ratio of total to high density lipoprotein cholesterol (< 4.5, 4.5-6.0, and > 6.0). Significant coronary artery disease (> or = 50% diameter stenosis in any major coronary artery) was present in 143 (16.9% prevalence). Overall sensitivity and specificity of 201Tl scintigraphy adjusted for verification bias were estimated to be 45 +/- 4% and 78 +/- 1%, respectively. These values are lower than corresponding values accepted for clinical populations. Positive and negative predictive values varied across subgroups. A normal thallium scan indicated low risk of disease, but an abnormal test was likely to be a false-positive result. A logistic equation was retrospectively fit to the data for estimating the probability of disease given age, cholesterol ratio, and thallium results. Within each quintile of estimated risk, the average risk did not differ significantly from the observed disease prevalence. CONCLUSIONS: Exercise 201Tl scintigraphy is limited by the frequent occurrence of false-positive tests in detecting asymptomatic, anatomic coronary artery disease in young men in accordance with Bayesian probability theory.

Adult↗
PubMed2006

Computation of madalines' sensitivity to input and weight perturbations.

The sensitivity of a neural network's output to its input and weight perturbations is an important measure for evaluating the network's performance. In this letter, we propose an approach to quantify the sensitivity of Madalines. The sensitivity is defined as the probability of output deviation due to input and weight perturbations with respect to overall input patterns. Based on the structural characteristics of Madalines, a bottom-up strategy is followed, along which the sensitivity of single neurons, that is, Adalines, is considered first and then the sensitivity of the entire Madaline network. By means of probability theory, an analytical formula is derived for the calculation of Adalines' sensitivity, and an algorithm is designed for the computation of Madalines' sensitivity. Computer simulations are run to verify the effectiveness of the formula and algorithm. The simulation results are in good agreement with the theoretical results.

Animals↗
PubMed1967

Blood ferrokinetics in normal man.

The clearance of radioiron from plasma and its appearance in circulating erythrocytes in normal subjects are studied. The importance of correcting for plasma iron fluctuations and for mean body hematocrit is illustrated. The data are analyzed by probability theory to determine relationships between intravascular and extravascular iron. Two refluxes are described, one of about 7 particles of every 100 leaving the plasma, and the second of about 23. The return times of these are about 5 hours and 8 days, respectively.

Adult↗
PubMed2004

In vivo MRS measurement of liver lipid levels in mice.

A magnetic resonance spectroscopy (MRS) procedure for in vivo measurement of lipid levels in mouse liver is described and validated. The method uses respiratory-gated, localized spectroscopy to collect proton spectra from voxels within the mouse liver. Bayesian probability theory analysis of these spectra allows the relative intensities of the lipid and water resonances within the liver to be accurately measured. All spectral data were corrected for measured spin-spin relaxation. A total of 48 mice were used in this study, including wild-type mice and two different transgenic mouse strains. Different groups of these mice were fed high-fat or low-fat diets or liquid diets with and without the addition of alcohol. Proton spectra were collected at baseline and, subsequently, every 4 weeks for up to 16 weeks. Immediately after the last MRS measurement, mice were killed and their livers analyzed for triglyceride level by conventional wet-chemistry methods. The excellent correlation between in vivo MRS and ex vivo wet-chemistry determinations of liver lipids validates the MRS method. These results clearly demonstrate that in vivo MRS will be an extremely valuable technique for longitudinal studies aimed at providing important insights into the genetic, environmental, and dietary factors affecting fat deposition and accumulation within the mouse liver.

Animals↗
PubMed1996

Do people with knowledge fake better?

Research on malingering that involves analog methods is frequently criticized for using normal subjects Critics have suggested that analog subjects probably perform differently from clinical Malingerers because of the absence of an identifiable incentive for analog malingerers, and because analog subjects have no opportunity to gain knowledge about the disorder to be malingered In contrast, clinical malingerers have an obvious incentive and may have at least a basic knowledge of the characteristics of the disorder they are feigning In this study, psychology graduate students and faculty were asked to malinger a memory deficit on several brief neuropsychological instruments on the premise that malingering would be difficult to detect in this population because of their supposed sophistication Results indicated that in sophisticated subjects, malingering was relatively easy to detect using indices of pattern of performance on standardized neuropsychological instruments, but more difficult to detect using instruments designed to detect malingering based on probability theory, and on specified knowledge of the effects of brain damage.

Journal Article↗
PubMed1987

Extracellular matrix and cell migration: locomotory characteristics of MOS-11 cells within a three-dimensional hydrated collagen lattice.

The locomotory trajectories of MOS-11 cells migrating in a three-dimensional hydrated collagen lattice have been determined using a computer-assisted optical sectioning unit. The trajectories have been quantified using a three-dimensional continuous-time Markov probability theory consisting of eight directional states and one stationary state; in the latter the cells are not locomoting. Markov analysis shows that these cells are locomoting in a random manner with regard to direction and remain stationary for about three times as long as they are locomoting. Analysis of persistence also implies random locomotion. Compilation of the distribution of angles between steps reveals that the cells exhibit a predilection for turns around 30 degrees and 150 degrees on either side of the previous step. Time-lapse video recordings show that the cells are bi-polar with ruffling membranes at opposite poles. Ruffling, and hence locomotion, occurs alternately at one pole and then the other, which would account for the distribution of angles encountered. The mean speed of the cells was of the order of 3 microns min-1 including the time stopped and approximately twice this if the time stopped (state 0) is not included. The results obtained provide base-line data on the locomotory characteristics of MOS-11 cells locomoting in a 1.2 mg ml-1 collagen gel. It is now possible to study the role of various matrix components in cell locomotion. Such studies are of importance to embryology, wound healing, host defence mechanisms and the invasion of cancer cells.

Animals↗
PubMed1995

Random drug tests at work: the probability of identifying frequent and infrequent users of illicit drugs.

Random drug testing in the workplace has become more common since federal guidelines were issued in 1988, despite the criticism that most positive tests are the result of occasional use of illicit drugs. In order to determine the relative probabilities of detecting frequent versus infrequent users of illicit drugs, a survey of 15 experts in the drug abuse field was conducted. Based on the responses, it was estimated that 55% of employed people who used any illicit drugs in the prior year were annual drug users, 37% were monthly users, and 8% were daily users. Analysis using probability theory indicated that among workplace drug users who test positive, 52% will be daily users, 41% will be monthly users, and only 7% will be annual users. At a 50% testing rate, random drug tests identify 40% of daily users, 8% of monthly users and only 1% of annual users during the course of a year. The estimated rate of illicit drug use among employees is approximately eight times the average random testing positive rate. Random drug tests in the workplace are effective in identifying near daily users of illicit drugs, but they are less effective at identifying infrequent drug users. Employers have found that random drug testing is a deterrent to both frequent and occasional use of illicit drugs.

Employment↗
PubMed2004

Bayesian neural-networks-based evaluation of binary speckle data.

We present a new method using Bayesian probability theory and neural networks for the evaluation of speckle interference patterns for an automated analysis of deformation and erosion measurements. The method is applied to the fringe pattern reconstruction of speckle measurements with a Twyman-Green interferometer. Given a binary speckle image, the method returns the fringe pattern without noise, thus removing the need for smoothing and allowing a straightforward unwrapping procedure and determination of the surface shape. Because no parameters have to be adjusted, the method is especially suited for continuous and automated monitoring of surface changes.

Journal Article↗
PubMed2002

Equivalence of cost generators for minimum cost flow phase unwrapping.

Phase unwrapping represents a crucial step in processing phase data obtained with techniques such as synthetic aperture radar interferometry, speckle interferometry, and magnetic resonance imaging. The so-called branch-cut approaches form an important class of phase unwrapping algorithms. In 1996, Costantini proposed to transform the problem of correctly placing branch cuts into a minimum cost flow problem [Proceedings of the Fringe '96 Workshop (European Space Agency, Munich, 1996), pp. 261-272]. The critical point of this new approach is to generate cost functions that have to represent all the a priori knowledge necessary for phase unwrapping. Any function transforming a priori knowledge into a cost function is called a cost generator. Several types of algorithms ranging from heuristic approaches to generators based on probability-theory interpretations were suggested. A problem arising from the growing diversity of algorithms is to find a criterion for the equivalence of different cost generators. Two cost generators are equivalent if they produce cost functions with the same minimal flow for every residue configuration on every image with all possible a priori knowledge. Comparing the results of different cost generators on test scenes can show only their non-equivalence. We solve this problem by proving the following mathematical classification theorem: Two cost generators are equivalent if and only if one can be transformed into the other by multiplication by a fixed constant.

Journal Article↗
PubMed1976

Nephelometric density adjustment of leptospiral antigen.

In testing leptospirosis by microagglutination, reproducibility of the results is affected by population age and germ concentration. These undersirable factors can be avoided if antibody identification is made with cultures incubated for 7 to 21 days and adjusted to 50 X 10(6) leptospires per millilitre. Most suitable for the purpose is an analogue mode based on nephelometry and the probability theory. The obtained statistical data furnish calculated and tabulated apparatus values which are used for standardizing with the aid of a newly developed nepheloflask with compression-spring stirrer.

Agglutination Tests↗
PubMed1999

[The functional interrelationships of blood glucose and immunoreactive insulin in the intravenous glucose tolerance test in coronary atherosclerosis patients].

Measurements of blood glucose and immunoreactive insulin (IRI) during glucose tolerance test (GTT) in patients with coronary atherosclerosis and with hereditary predisposition to this condition were carried out. The results were processed using programs based on the least squares method, theoretically based on the main assumptions of the probability theory. A strong (virtually linear) correlation between glucose and IRI was detected in the studied groups. Shift of the glucose level by 1 unit in patients with coronary atherosclerosis leads to an almost twofold increase in IRI level, as against subjects with hereditary liability to coronary atherosclerosis. Nonlinear relationship between glucose and IRI in the GTT is described for the control group.

Adult↗