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Results for “Model interpretability”

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PubMed2002

[Sensitivity and parameters of the otolith as a spatially distributed system].

Comparison of the de Vries pendulum and spatially distributed otolith models allowed physical interpretation of the pendulum model parameters and determination of the influence of otolith structure on its mechanical sensitivity when otolith dynamics is represented by a parallel displacement relative to the receptor surface. Proof was obtained that in this case otolith dynamics is independent of total mass, and mechanic sensitivity is not proportional to size of the organ. Possible explanations of the effects of changed dynamics conditions on otolith parameters in the fish are discussed.

Animals↗

PubMed1990

[Strategies in the use of isolated cardiomyocytes in relation to other models in experimental cardiology].

Selection of the optimal model for a specific experiment considerably determines the results and their correct interpretation. The model of the isolated cardiomyocyte is increasingly being used in experimental cardiology as it provides several advantages in comparison to models in which the heart tissue remains relatively complete. Similarly as in other models, the factors limiting its use have to be known also in the case of the isolated cardiomyocyte. To minimalize misinterpretation of results the given problem is to be handled at all available levels.

Heart↗

PubMed1987

Mass transport in dissolution kinetics. I: Convective diffusion to assess the role of fluid viscosity under forced flow conditions.

The quantitative influence of viscosity on dissolution kinetics is assessed under laminar flow conditions by utilizing a convective diffusion model for drug dissolution. Functional dependency of three types of viscosity inducing agents is established with respect to the parameters of fluid flow rate, diffusivity, and solubility. Studies of aqueous solutions of sucrose and of glycerol demonstrate that the decrease in dissolution rate of ethyl p-aminobenzoate is related to the decrease in solute diffusivity in these solutions, whereas the solubility change in the glycerol solutions has an additional independent simultaneous effect. Dissolution in hydroxypropyl cellulose solutions remains constant under fixed fluid flow conditions because of the negligible effect of the polymer upon the drug diffusivity. A change in fluid flow rate, however, alters the dissolution rate and correlates quantitatively with the rate of shear in the convective diffusion model. The interpretation of the effect of viscosity on dissolution kinetics with the convective diffusion model explains these phenomena quantitatively in terms of the fundamental mass transport processes.

Cellulose↗

PubMed2005

The influence of geographic location on population exposure to emissions from power plants throughout China.

This analysis seeks to evaluate the influence of emission source location on population exposure in China to fine particles and sulfur dioxide. We use the concept of intake fraction, defined as the fraction of material or its precursor released from a source that is eventually inhaled or ingested by a population. We select 29 power-plant sites throughout China and estimate annual average intake fractions at each site, using identical source characteristics to isolate the influence of geographic location. In addition, we develop regression models to interpret the intake fraction values and allow for extrapolation to other sites. To model the concentration increase due to emissions from selected power plants, we used a detailed long-range atmospheric dispersion model, CALPUFF. Primary fine particles have the highest average intake fraction (1 x 0(-5)), followed by sulfur dioxide (5 x 10(-6)), sulfate from sulfur dioxide (4 x 10(-6)), and nitrate from nitrogen oxides (4 x 10(-6)). For all pollutants, the intake fractions span approximately an order of magnitude across sites. In the regression analysis, the independent variables are meteorological proxies (such as climate region and precipitation) and population at various distances from the source. We find that population terms can explain a substantial percentage of variability in the intake fraction for all pollutants (R(2) between 0.86 and 0.95 across pollutants), with a significant modifying influence of meteorological regime. Near-source population is more important for primary coarse particles while population at medium to long distance is more important for primary fine particles and secondary particles. A significant portion of intake fraction (especially for secondary particles and primary fine particles) occurs beyond 500 km of the source, emphasizing the need for detailed long-range dispersion modeling. These findings demonstrate that intake fractions for power plants in China can be estimated with reasonable precision and summarized using simple regression models. The results should be useful for informing future decisions about power-plant locations and controls.

Air Pollutants↗

PubMed2003

Review of methods and computer codes for interpretation of bioassay data.

Internal dose determination is an essential component of individual monitoring programmes for workers or members of the public exposed to radionuclides, and methods and computer programs are required for dose assessment. A recent international European Radiation Dosimetry Group (EURADOS) intercomparison has shown unacceptably large ranges in the results assessment. An ICRP working party has been initiated to consider what guidance ICRP can give on the use of models and interpret bioassay data in terms of intake/dose. In this field, six codes for bioassay data interpretation, which implement the current ICRP publication 78 biokinetic models, have been reviewed against several criteria with different levels of importance: minor criteria such as the practical use of the code and the graphical capabilities, and major criteria such as the choice of available parameters, peculiarities of data fitting and interpretation, the choice of biokinetic models and the use of uncertainties. All these criteria were assessed using one artificial set of data and two examples extracted from the previous international EURADOS intercomparison.

Administration, Oral↗

PubMed2001

On the Interpretation of Response Time vs Onset Asynchrony Functions: Application to Dual-Task and Precue-Utilization Paradigms.

The central bottleneck model of dual-task performance (H. Pashler and J. C. Johnston, 1998, Quarterly Journal of Experimental Psychology, 46A, 51-82) and the serial processing model of precue utilization (R. Gottsdanker, 1992, Acta Psychologica, 79, 21-43) are based on a common formal structure: They both represent response time as RT(tau)=max(X-tau, Y)+Z, where X, Y, Z denote the duration of certain processing stages specified by the models and tau denotes the onset asynchrony (SOA) between two stimuli. We consider this model within a stochastic framework in which the stage durations are random variables following an arbitrary joint distribution and derive properties of the function relating E[RT(tau)] to SOA. We present a distribution-free result which relates the slope of this function to the distribution of the random durations of the assumed processing stages. Our results allow for a direct, model-based interpretation of data from related experiments; specifically, they show how the slope of the SOA-function depends on experimental factors which selectively influence individual processing stages. We explain the implications of our results for models of dual-task performance and precue utilization and illustrate their application to data obtained by M. C. Smith (1969, Acta Psychologica, 30, 220-231) and R. Gottsdanker (1992, loc. cit.) Copyright 2001 Academic Press.

Journal Article↗

PubMed1986

Interpretation of oxygen disappearance curves measured in blood perfused tissues.

We have developed a two compartment (tissue and blood) lumped parameter model to interpret oxygen disappearance curves (O2 DCs) measured in vivo with PO2 microelectrodes in tissues which are perfused with blood. To include the properties of the oxyhemoglobin equilibrium curve (HEC), we used an algorithm we have recently developed for both standard and nonstandard conditions. The new blood and tissue model is more useful than a previous analysis using the Hill equation for blood and constant oxygen consumption (VO2). The model can be adapted for constant (zero-order) consumption, Michelis-Menten kinetics, or for double cytochrome systems. Examples for the former include brain, and for the latter, carotid body. The models are discussed in relationship to experimental microelectrode measurements in gerbil brain and in cat carotid body after blood flow occlusion.

Animals↗

PubMed2000

Regularities in mutational variability in selected protein families and the Markovian model of amino acid replacement.

Three families of proteinase inhibitors and the trypsin family were the subjects of the analysis of amino acid replacements at aligned positions. This approach concerned some specific types of replacement and the mechanisms that can be involved in their control. The usefulness of the Markovian model for interpretation of mutational replacement within homologous proteins was examined. The same sequences were also analyzed with the use of the non-Markovian algorithm of genetic semihomology. This study leads to the conclusion that the Markovian model is not suitable for the interpretation of protein mutational variability since: (1) The information about the history of a variable unit is included in its genetic code. (2) This information plays an important role in the probability of further possible changes of the unit.

Algorithms↗

PubMed1997

Computer analysis of two-dimensional electrophoresis gels: a new segmentation and modeling algorithm.

The complexity of the spot patterns of two-dimensional electrophoresis gels made it necessary to use image processing techniques to analyze the gels. An important issue in the analysis is the detection and quantification of the protein spots. In this paper we describe a new technique to segment and model the different spots. For the segmentation of a gel into its different spot regions we apply a watershed technique, which is robust and efficient. For the quantification of the spots, a new spot model is constructed, based on diffusion principles. Besides the advantage of having a physical interpretation, the model is demonstrated to be superior to the commonly used Gaussian models.

Algorithms↗

PubMed2006

Modeling of soiling based on silica-soda-lime glass exposure at six European sites.

Samples of silica-soda-lime float glass, a material selected as a pertinent soiling sensor, were exposed for up to 28 months at four urban sites (Athens, Krakow, London and Prague) and at a semi-urban one (Monte Libretti, near Rome), sheltered from rain. This exhaustive experience permitted to complete and to test the generalisation ability of the results previously obtained on the same material, exposed according to the same protocol, during 24 months, at a single site (Paris). The model previously fitted for the Paris experiment, the Hill equation, could be successfully generalised for four other sites of exposure (Athens, Krakow, Prague and Rome). The analytical form of this model was interpreted in terms of a physical description of the soiling phenomenon. Some of the model coefficients were different from one site to another, depending on the specific environment of exposure (air pollution levels, meteorological factors), while the other ones were rather equivalent. The analysis of the model coefficients, on the one hand, led to an estimation of the period after which soiling is close to its saturation level, and on the other hand, it will permit to correlate these coefficients to the environmental factors, in order to select the most appropriate ones for building dose-response functions for soiling, with broad geographical application.

Journal Article↗

PubMedDate not supplied

A model for case assessment and interpretation.

The authors describe a new approach to decision-making in an operational forensic science organization based on a model, embodying the principles of Bayesian inference, which has been developed through workshops run within the Forensic Science Service for forensic science practitioners. Issues which arise from the idea of pre-assessment of cases are explored by means of a case example.

Bayes Theorem↗

PubMed1991

Utility of phenomenological models for describing temperature dependence of bacterial growth.

We compared three unstructured mathematical models, the master reaction, the square root, and the damage/repair models, for describing the relationship between temperature and the specific growth rates of bacteria. The models were evaluated on the basis of several criteria: applicability, ease of use, simple interpretation of model parameters, problem-free determination of model parameters, statistical evaluation of goodness of fit (chi 2 test), and biological relevance. Best-fit parameters for the master reaction model could be obtained by using two consecutive nonlinear least-square fits. The damage/repair model proved to be unsuited for the data sets considered and was judged markedly overparameterized. The square root model allowed nonproblematical parameter estimation by a nonlinear least-square procedure and, together with the master reaction model, was able to describe the temperature dependence of the specific growth rates of Klebsiella pneumoniae NCIB 418, Escherichia coli NC3, Bacillus sp. strain NCIB 12522, and the thermotolerant coccobacillus strain NA17. The square root and master reaction models were judged to be equally valid and superior to the damage/repair model, even though the square root model is devoid of a conceptual basis.

Bacteria↗

PubMed1989

A strategy for analysing multiple risk factors with application to cervical pain syndrome.

When studying the possible effects of several factors in a given disease, two major problems arise: (1) confounding, and (2) multiplicity of tests. Frequently, in order to cope with the problem of confounding factors, models with multiple explanatory variables are used. However, the correlation structure of the variables may be such that the corresponding tests have low power: in its extreme form this situation is coined by the term "multicollinearity". As the problem of multiplicity is still relevant in these models, the interpretation of results is, in most cases, very hazardous. We propose a strategy--based on a tree structure of the variables--which provides a guide to the interpretation and controls the risk of erroneously rejecting null hypotheses. The strategy was applied to a study of cervical pain syndrome involving 990 subjects and 17 variables. Age, sex, head trauma, posture at work and psychological status were all found to be important risk factors.

Adult↗

PubMed2006

Realistic modeling of entorhinal cortex field potentials and interpretation of epileptic activity in the guinea pig isolated brain preparation.

Mechanisms underlying epileptic activities recorded from entorhinal cortex (EC) were studied through a computational model based on review of cytoarchitectonic and neurobiological data about this structure. The purpose of this study is to describe and use this model to interpret epileptiform discharge patterns recorded in an experimental model of ictogenesis (guinea pig isolated brain perfused with bicuculline). A macroscopic modeling approach representing synaptic interactions between cells subpopulations in the EC was chosen for its adequacy to mimic field potentials reflecting overall dynamics rising from interconnected cells populations. Therefore intrinsic properties of neurons were not included in the modeling design. Model parameters were adjusted from an identification procedure based on quantitative comparison between real and simulated signals. For both EC deep and superficial layers, results show that the model generates very realistic signals regarding temporal dynamics, spectral features, and cross-correlation values. These simulations allowed us to infer information about the evolution of synaptic transmission between principal cell and interneuronal populations and about connectivity between deep and superficial layers during the transition from background to ictal activity. In the model, this transition was obtained for increased excitation in deep versus superficial layers. Transitions between epileptiform activities [interictal spikes, fast onset activity (25 Hz), ictal bursting activity] were explained by changes of parameters mainly related to GABAergic interactions. Notably, the model predicted an important role of GABAa,fast- and GABAb-receptor-mediated inhibition in the generation of ictal fast onset and burst activities, respectively. These findings are discussed with respect to experimental data.

Action Potentials↗

PubMedDate not supplied

A four-compartment model for Ca2+ dynamics: an interpretation of Ca2+ decay after repetitive firing of intact nerve terminals.

In the presynaptic nerve terminals of the bullfrog sympathetic ganglia, repetitive nerve firing evokes [Ca2+] transients that decay monotonically. An algorithm based on an eigenfunction expansion method was used for fitting these [Ca2+] decay records. The data were fitted by a linear combination of two to four exponential functions. A mathematical model with three intraterminal membrane-bound compartments was developed to describe the observed Ca2+ decay. The model predicts that the number of exponential functions, n, contained in the decay data corresponds to n-1 intraterminal Ca2+ stores that release Ca2+ during the decay. Moreover, when a store stops releasing or starts to release Ca2+, the decay data should be fitted by functions that contain one less exponential component for the former and one more for the latter than do the fitting functions for control data. Because of the current lack of a parameter by which quantitative comparisons can be made between two decay processes when at least one of them contained more than one exponential components, we defined a parameter, the overall rate (OR) of decay, as the trace of the coefficient matrix of the differential equation systems of our model. We used the mathematical properties of the model and of the OR to interpret effects of ryanodine and of a mitochondria uncoupler on Ca2+ decay. The results of the analysis were consistent with the ryanodine-sensitive store, mitochondria, and another, yet unidentified store release Ca2+ into the cytosol of the presynaptic nerve terminals during Ca2+ decay. Our model also predicts that mitochondrial Ca2+ buffering accounted for more than 86% of all the flux rates across various membranes combined and that there are type 3 and type 1 and/or type 2 ryanodine receptors in these terminals.

Action Potentials↗

PubMed2000

Interpreting parameters in the logistic regression model with random effects.

Logistic regression with random effects is used to study the relationship between explanatory variables and a binary outcome in cases with nonindependent outcomes. In this paper, we examine in detail the interpretation of both fixed effects and random effects parameters. As heterogeneity measures, the random effects parameters included in the model are not easily interpreted. We discuss different alternative measures of heterogeneity and suggest using a median odds ratio measure that is a function of the original random effects parameters. The measure allows a simple interpretation, in terms of well-known odds ratios, that greatly facilitates communication between the data analyst and the subject-matter researcher. Three examples from different subject areas, mainly taken from our own experience, serve to motivate and illustrate different aspects of parameter interpretation in these models.

Animals↗

PubMed2003

Correlations between small aperture skin suction parameters: statistical analysis and mechanical model.

BACKGROUND/AIMS: Skin suction experiments are widely used in order to evaluate the effects of skin treatments, both for cosmetic and for dermatological purposes. Classically, the elevation of the skin is measured at different discrete time instances after the pressure has been changed. Relations between the classical parameters - Uv, Ur, Ue and Uf - have been investigated and used in order to develop a new model for interpreting the mechanical properties of the skin. METHODS: Within a group of 68 female subjects - aged between 37 and 68 - a Cutometer has been used in order to determine classical skin suction parameters on the female facial skin. Each skin suction measurement consists of three consecutive underpressure cycles. Within the resulting parameter set, a statistical analysis has been performed to investigate interparameter relations. RESULTS: Strong interparameter correlations have been found within a set of 12 classical skin suction parameters. The set contains three independent groups of interrelated parameters. Based on this observation, a one-dimensional mechanical model - consisting of springs and dampers - is constructed. When two extra independent parameters are included in the model, the elevation versus time curves as recorded during three consecutive underpressure cycles can be fully described. The model reveals that typical skin suction data can be described in terms of a quick and a slow deformation process. The two characteristic time scales are 0.1 and 7 s approximately. The 0.1 s-value matches the response time of the device used. In reality, the quick deformation process in the skin may have a shorter time scale. CONCLUSIONS: In skin suction data, each underpressure cycle is usually characterized by four classical parameters - Uv, Ur, Ue and Uf. Within the 12 parameters of a three-cycle measurement, three independent groups of interrelated parameters have been found. These groups can be represented by the parameters Uv1, Ur1 and Uf1 of the first underpressure cycle. A model that is based on these three independent groups and two other independent parameters is proposed. The model provides an accurate description of the skin deformation as recorded during a measurement involving three underpressure cycles. The model is an improvement over classical interpretations of skin suction data where interrelated parameters are used. Moreover, the five-parameter model accounts for well-known mechanical characteristics of the skin such as preconditioning and visco-elastic behavior.

Adaptation, Physiological↗

PubMed1998

Interpreting comparative experiments on parasite burdens in animals using randomization and canonical variates.

Comparative experiments on parasite burdens present difficulties for modelling and interpretation: data tend to have highly skewed distributions, some standard methods of testing for effects have low power, and there is a need to make allowance for dependencies among the various measurements. Randomization testing and canonical variates analysis are advocated as a means of minimising these problems.

Abomasum↗