Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “model selection”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources

On the use of Bayesian methods for evaluating compartmental neural models.

Computational modeling is being used increasingly in neuroscience. In deriving such models, inference issues such as model selection, model complexity, and model comparison must be addressed constantly. In this article we present briefly the Bayesian approach to inference. Under a simple set of commonsense axioms, there exists essentially a unique way of reasoning under uncertainty by assigning a degree of confidence to any hypothesis or model, given the available data and prior information. Such degrees of confidence must obey all the rules governing probabilities and can be updated accordingly as more data becomes available. While the Bayesian methodology can be applied to any type of model, as an example we outline its use for an important, and increasingly standard, class of models in computational neuroscience--compartmental models of single neurons. Inference issues are particularly relevant for these models: their parameter spaces are typically very large, neurophysiological and neuroanatomical data are still sparse, and probabilistic aspects are often ignored. As a tutorial, we demonstrate the Bayesian approach on a class of one-compartment models with varying numbers of conductances. We then apply Bayesian methods on a compartmental model of a real neuron to determine the optimal amount of noise to add to the model to give it a level of spike time variability comparable to that found in the real cell.

Action Potentials↗

Correlations between patient-controlled epidural analgesia requirements and individual characteristics among gynecologic patients.

BACKGROUND: Patient-controlled epidural analgesia (PCEA) has been used widely to relieve postoperative pain. Although many studies have demonstrated the safety and effectiveness of PCEA, the relationship between patients' characteristics and requirements of PCEA has not been investigated yet. We conducted this retrospective study to explore the correlations between total PCEA demand and patients' characteristics. METHODS: We collected data from patients aged from 20 to 65, receiving gynecologic operations and consenting to epidural analgesia. All patients used postoperative PCEA for at least 3 days. An analgesic solution of bupivacaine (0.0625%) and morphine (0.02 mg/mL) was prepared for PCEA in all patients. The total PCEA consumption was recorded at the end of the 3-day course. Stepwise regression analysis was conducted to sort out influential factors which could determine the total PCEA demand. RESULTS: There were 170 patients (81 benign and 89 malignant cases) included in the analysis. Significant differences existed in age and total PCEA requirement between different disease patterns. The stepwise regression model selection showed that disease patterns, body mass index (BMI) and age were most significant determinants of total PCEA demand. The R and adjusted R square values of the final selected model are 0.339 and 0.099, respectively. The comparison between the standardized regression coefficient of BMI and age suggested that the influence of BMI is greater than that of age. CONCLUSIONS: Disease patterns, BMI and age are associated with total PCEA requirements. Gynecologic patients receiving procedures for malignant diseases consumed more PCEA solution than benign cases. Height is not associated with total PCEA demand. There is a close correlation between BMI and PCEA consumption but age is a negative correlate.

Adult↗

The neurobiology of alcoholism in genetically selected rat models.

Rats selectively bred for their tendency to drink large or small quantities of alcohol are a useful model for investigators examining the possible neurobiological processes underlying alcoholism. Studies with the alcohol-preferring (P) and alcohol-nonpreferring (NP) and the high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) pairs of rat lines developed at Indiana University have illustrated differences in several behavioral and neurobiological characteristics associated with alcohol consumption. Specifically, compared with alcohol-avoiding rats, rats with an affinity for alcohol have a greater sensitivity to the stimulatory effects of low to moderate doses and a reduced sensitivity to the negative effects of high doses. Rats that voluntarily drink large quantities of alcohol also acquire tolerance to alcohol's aversive effects. In addition, these rats differ from their alcohol-avoiding counterparts in the levels of several chemical mediators (i.e., neurotransmitters) found in the brain, including serotonin, dopamine, gamma-aminobutyric acid (GABA), and the endogenous opioids.

Alcohol Drinking↗

Selection among nonlinear models for rate of passage studies in ruminants.

Eight Toggenburg wether goats were fed either Coastal bermudagrass (Cynodon dactylon) or orchardgrass (Dactylis glomerata)-alfalfa (Medicago sativa) hay (57:43%) in a reversal design. Four markers were used to study the movement of different digesta fractions: erbium for large particles greater than 1,700 microns; ytterbium for medium particles less than 1,700 microns and greater than 500 microns; chromium for small particles less than 500 microns and greater than 32 microns; and cobalt to follow liquid passage. Fecal samples were collected every 4 h for 6 d. The excretion curves obtained for every marker in each animal were used for model selection. One-compartment gamma age-dependent models (gamma 2, 3 and 4 age-dependent), two-compartment (gamma 2 and gamma 3 age-dependent, age-independent) models and a biexponential model were fitted to the data. Residual sums of squares and the Davidson and MacKinnon test were used to select the most appropriate models. These procedures indicated that the models best describing the movement of different digesta fractions through the gastrointestinal tract of goats, in this experiment, were the biexponential model for liquids, gamma 2 two-compartment model for small and medium particles and gamma 3 two-compartment model for large particles. To accurately describe the behavior of different components of digesta in the digestive tract, different mathematical models are required. In general, models that describe the movement of large particles have higher orders of age-dependency than models that describe the passage of liquids or small particles.

Animal Feed↗

The effect of branch length variation on the selection of models of molecular evolution.

Models of sequence evolution play an important role in molecular evolutionary studies. The use of inappropriate models of evolution may bias the results of the analysis and lead to erroneous conclusions. Several procedures for selecting the best-fit model of evolution for the data at hand have been proposed, like the likelihood ratio test (LRT) and the Akaike (AIC) and Bayesian (BIC) information criteria. The relative performance of these model-selecting algorithms has not yet been studied under a range of different model trees. In this study, the influence of branch length variation upon model selection is characterized. This is done by simulating sequence alignments under a known model of nucleotide substitution, and recording how often this true model is recovered by different model-fitting strategies. Results of this study agree with previous simulations and suggest that model selection is reasonably accurate. However, different model selection methods showed distinct levels of accuracy. Some LRT approaches showed better performance than the AIC or BIC information criteria. Within the LRTs, model selection is affected by the complexity of the initial model selected for the comparisons, and only slightly by the order in which different parameters are added to the model. A specific hierarchy of LRTs, which starts from a simple model of evolution, performed overall better than other possible LRT hierarchies, or than the AIC or BIC.

Bayes Theorem↗

Some statistical issues related to multiple linear regression modeling of beach bacteria concentrations.

As a fast and effective technique, the multiple linear regression (MLR) method has been widely used in modeling and prediction of beach bacteria concentrations. Among previous works on this subject, however, several issues were insufficiently or inconsistently addressed. Those issues include the value and use of interaction terms, the serial correlation, the criteria for model selection, and model assessment. The present work shows that serial correlations, as often present in sequentially observed data records, deserve full attention from the modeler. The testing and adjustment for the time-series effect should be implemented in a statistically rigorous framework. The R(2) and Cp-statistic as joint criteria are recommended for the model selection process, while using the t-statistics associated with the full model is erroneous. During model selection, using interaction terms can often help to decrease the bias in reduced models, although the resulting improvement in the numerical performance may be limited. For the assessment of the model predictive capacity, which is different from testing the goodness of fit, a comprehensive set of statistics are advocated to allow for an objective evaluation of different models. Results obtained from the data at Huntington Beach, OH, show that erroneous conclusions could be drawn if only the model R(2) and the count of type I and type II errors are considered. In this sense, several previous works deserve further investigation.

Bathing Beaches↗

Error criteria for cross validation in the context of chaotic time series prediction.

The prediction of a chaotic time series over a long horizon is commonly done by iterating one-step-ahead prediction. Prediction can be implemented using machine learning methods, such as radial basis function networks. Typically, cross validation is used to select prediction models based on mean squared error. The bias-variance dilemma dictates that there is an inevitable tradeoff between bias and variance. However, invariants of chaotic systems are unchanged by linear transformations; thus, the bias component may be irrelevant to model selection in the context of chaotic time series prediction. Hence, the use of error variance for model selection, instead of mean squared error, is examined. Clipping is introduced, as a simple way to stabilize iterated predictions. It is shown that using the error variance for model selection, in combination with clipping, may result in better models.

Journal Article↗

A model for background selection in non-equilibrium populations.

In many taxa, levels of genetic diversity are observed to vary along their genome. The framework of background selection models this variation in terms of linkage to constrained sites, and recent applications have been able to explain a large portion of the variation in human genomes. However, these studies have also yielded conflicting results, stemming from two key limitations. First, existing models are inaccurate in a critical region of parameter space (), where the local reduction in diversity is sharpest. Second, they assume a constant population size over time. Here, we develop predictions for diversity under background selection based on the Hill-Robertson system of two-locus statistics, which allows for population size changes. We treat the joint effect of multiple selected loci independently, but we show that interference among them is well captured through local rescaling of mutation, recombination and selection in an iterative procedure that converges quickly. We further accommodate existing background selection theory to non-equilibrium demography, bridging the gap between weak and strong selection. Simulations show that our predictions are accurate across the entire range of selection coefficients. We characterize the temporal dynamics of linked selection under population size changes and demonstrate that patterns of diversity can be misinterpreted by other models. Specifically, biases due to the incorrect assumption of equilibrium carry over to downstream inferences of the distribution of fitness effects and deleterious mutation rate. Jointly modeling demography and linked selection therefore improves our understanding of the genomic landscape of diversity, which will help refine inferences of linked selection in humans and other species.

Journal Article↗

The chimpanzee (Pan troglodytes) as a pharmacokinetic model for selection of drug candidates: model characterization and application.

The chimpanzee (CHP) was evaluated as a pharmacokinetic model for humans (HUMs) using propranolol, verapamil, theophylline, and 12 proprietary compounds. Species differences were observed in the systemic clearance of theophylline (approximately 5-fold higher in CHPs), a low clearance compound, and the bioavailability of propranolol and verapamil (lower in CHPs), both high clearance compounds. The systemic clearance of propranolol (approximately 1.53 l/h/kg) suggested that the hepatic blood flow in CHPs is comparable to that in humans. No substantial differences were observed in the in vitro protein binding. A preliminary attempt was made to characterize cytochrome P450 (P450) activities in CHP and HUM liver microsomes. Testosterone 6beta-hydroxylation and tolbutamide methylhydroxylation activities were comparable in CHP and HUM liver microsomes. In contrast, dextromethorphan O-demethylation and phenacetin O-deethylation activities were approximately 10-fold higher (per mg protein) in CHP liver microsomes. Intrinsic clearance estimates in CHP liver microsomes were higher for propranolol (approximately 10-fold) and theophylline (approximately 5-fold) and similar for verapamil. Of the 12 proprietary compounds, 3 had oral clearances that differed in the two species by more than 3-fold, an acceptable range for biological variability. Most of the observed differences are consistent with species differences in P450 enzyme activity. Oral clearances of proprietary compounds in HUMs were significantly correlated to those from CHPs (r = 0.68; p = 0.015), but not to estimates from rat, dog, and monkey. In summary, the chimpanzee serves as a valuable surrogate model for human pharmacokinetics, especially when species differences in P450 enzyme activity are considered.

Acetaminophen↗

A test of Kinsbourne's selective activation model.

Kinsbourne's selective activation model (1985) was investigated in a sample of 28 strongly right-dominant males. Priming manipulations were hypothesized preferentially to activate a hemisphere and to decrease reaction time on an affect recognition task in the contralateral visual field. The left hemisphere manipulation consisted of subvocal verbal rehearsal, while imagery served as the right hemisphere task. Baseline performance was evaluated via a control condition. No priming was found, but the experimental tasks had significant interference effects. Interference was noted across visual fields for both experimental manipulations relative to the control condition, suggesting the hemispheres were not preferentially recruited. Furthermore, the processing of happy faces was more susceptible to interference than was that of angry faces. Conceptual and methodological issues are presented to account for the former finding and data relevant to the laterality of affect perception may explain the latter.

Adult↗

Reliability of reasons for early termination of breastfeeding: application of a bivariate probability model with sample selection to data from surveys in Malaysia in 1976-77 and 1988-89.

Although extensively collected, data on people's reasons for their behaviour provided retrospectively have been met with some scepticism on the grounds that they may be subject to biases and errors that jeopardize their usefulness. This study investigates, for a sample of 1,327 births, the reliability with which women in Peninsular Malaysia recalled, at intervals 12 years apart, reasons for not initiating or for stopping breastfeeding less than 3 months after a birth. Overall, we find low to moderate reliability of recall. Levels of reliability are relatively high for some reasons (the child died and no or insufficient milk) but low for some others (child ill, breastfeeding inconvenient). Results from selection models show that reliability does not vary with the length of time since the child's birth but is inversely related to socio-economic status (proxied by education and employment). Social status, social norms, and health-related factors appear to be significant influences on women's consistency of reporting.

Breast Feeding↗

Motion estimation using Statistical Learning Theory.

This paper describes a novel application of Statistical Learning Theory (SLT) to single motion estimation and tracking. The problem of motion estimation can be related to statistical model selection, where the goal is to select one (correct) motion model from several possible motion models, given finite noisy samples. SLT, also known as Vapnik-Chervonenkis (VC), theory provides analytic generalization bounds for model selection, which have been used successfully for practical model selection. This paper describes a successful application of an SLT-based model selection approach to the challenging problem of estimating optimal motion models from small data sets of image measurements (flow). We present results of experiments on both synthetic and real image sequences for motion interpolation and extrapolation; these results demonstrate the feasibility and strength of our approach. Our experimental results show that for motion estimation applications, SLT-based model selection compares favorably against alternative model selection methods, such as the Akaike's fpe, Schwartz' criterion (sc), Generalized Cross-Validation (gcv), and Shibata's Model Selector (sms). The paper also shows how to address the aperture problem using SLT-based model selection for penalized linear (ridge regression) formulation.

Algorithms↗

Ion selective transistor modelling for behavioural simulations.

Computer aided design and simulation of complex silicon microsystems oriented for environment monitoring requires efficient and accurate models of ion selective sensors, compatible with the existing behavioural simulators. This paper concerns sensors based on the back-side contact Ion Sensitive Field Effect Transistors (ISFETs). The ISFETs with silicon nitride gate are sensitive to hydrogen ion concentration. When the transistor gate is additionally covered with a special ion selective membrane, selectivity to other than hydrogen ions can be achieved. Such sensors are especially suitable for flow analysis of solutions containing various ions. The problem of ion selective sensor modelling is illustrated here on a practical example of an ammonium sensitive membrane. The membrane is investigated in the presence of some interfering ions and appropriate selectivity coefficients are determined. Then, the model of the whole sensor is created and used in subsequent electrical simulations. Providing that appropriate selectivity coefficients are known, the proposed model is applicable for any membrane, and can be straightforwardly implemented for behavioural simulation of water monitoring microsystems. The model has been already applied in a real on-line water pollution monitoring system for detection of various contaminants.

Computer Simulation↗

Modelling land use change with generalized linear models--a multi-model analysis of change between 1860 and 2000 in Gallatin Valley, Montana.

This paper develops an approach to modelling land use change that links model selection and multi-model inference with empirical models and GIS. Land use change is frequently studied, and understanding gained, through a process of modelling that is an empirical analysis of documented changes in land cover or land use patterns. The approach here is based on analysis and comparison of multiple models of land use patterns using model selection and multi-model inference. The approach is illustrated with a case study of rural housing as it has developed for part of Gallatin County, Montana, USA. A GIS contains the location of rural housing on a yearly basis from 1860 to 2000. The database also documents a variety of environmental and socio-economic conditions. A general model of settlement development describes the evolution of drivers of land use change and their impacts in the region. This model is used to develop a series of different models reflecting drivers of change at different periods in the history of the study area. These period specific models represent a series of multiple working hypotheses describing (a) the effects of spatial variables as a representation of social, economic and environmental drivers of land use change, and (b) temporal changes in the effects of the spatial variables as the drivers of change evolve over time. Logistic regression is used to calibrate and interpret these models and the models are then compared and evaluated with model selection techniques. Results show that different models are 'best' for the different periods. The different models for different periods demonstrate that models are not invariant over time which presents challenges for validation and testing of empirical models. The research demonstrates (i) model selection as a mechanism for rating among many plausible models that describe land cover or land use patterns, (ii) inference from a set of models rather than from a single model, (iii) that models can be developed based on hypothesised relationships based on consideration of underlying and proximate causes of change, and (iv) that models are not invariant over time.

Agriculture↗

Selecting a model system for neurobiological studies of learning and memory.

This article discusses the logic underlying the use of invertebrate model systems for investigating the neurobiological basis of learning and memory, the kinds of questions which can be asked of these systems as well as their limitations. A model system selected to answer specific questions about learning and memory is most useful if its selection is based on strategy rather than chance.

Animals↗

Statistical Tests for Comparing Possibly Misspecified and Nonnested Models.

Model selection criteria (MSC) involves selecting the model with the best estimated goodness-of-fit to the data generating process. Following the method of Vuong (1989), a large sample Model Selection Test (MST), is introduced that can be used in conjunction with most existing MSC procedures to decide if the estimated goodness-of-fit for one model is significantly different from the estimated goodness-of-fit for another model. The MST extends the classical generalized likelihood ratio test, is valid in the presence of model misspecification, and is applicable to situations involving nonnested probability models. Simulation studies designed to illustrate the concept of the MST and its conservative decision rule (relative to the MSC method) are also presented. Copyright 2000 Academic Press.

Journal Article↗

A quantitative model of optimal data selection in Wason's selection task.

The optimal data selection model proposed by Oaksford and Chater (1994) successfully formalized Wason's selection task (Wason, 1966). The model, however, involved some questionable assumptions and was also not sufficient as a model of the task because it could not provide quantitative predictions of the card selection frequencies. In this paper, the model was revised to provide quantitative fits to the data. The model can predict the selection frequencies of cards based on a selection tendency function (STF), or conversely, it enables the estimation of subjective probabilities from data. Past experimental data were first re-analysed based on the model. In Experiment 1, the superiority of the revised model was shown. However, when the relationship between antecedent and consequent was forced to deviate from the biconditional form, the model was not supported. In Experiment 2, it was shown that sufficient emphasis on probabilistic information can affect participants' performance. A detailed experimental method to sort participants by probabilistic strategies was introduced. Here, the model was supported by a subgroup of participants who used the probabilistic strategy. Finally, the results were discussed from the viewpoint of adaptive rationality.

Adult↗