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Results for “Model performance”

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PubMed1993

Quality of laboratory performance in testing for human immunodeficiency virus type 1 antibody. Identification of variables associated with laboratory performance.

To identify factors that may affect the quality of laboratory performance of human immunodeficiency virus type 1 (HIV-1) antibody testing, the Centers for Disease Control and Prevention Model Performance Evaluation Program surveyed laboratories in 1989 that performed enzyme immunoassay (EIA) and Western blot tests for HIV-1 antibody. Panels of 10 HIV-1-antibody-positive and antibody-negative plasma samples, some of which were duplicates, were mailed to program-participating laboratories. Laboratories were also mailed survey questionnaires to ascertain their laboratory characteristics and testing practices. Using 1988 data, researchers previously found that the overall analytic performance of laboratories performing HIV-1 antibody testing was independently associated with the following: (1) requiring a minimum degree of testing personnel; (2) having written criteria for identifying unsatisfactory specimens; (3) requiring in-house training for testing personnel; (4) having tested more than 10,000 specimens; (5) being identified as an "other" laboratory type; (6) having more than 24 months of testing experience; (7) laboratory uses specific (Abbott) materials for EIA; and (8) testing specimens collected by family-planning clinics. To verify these findings, we performed multivariate analysis on 1989 performance data. For the 1989 EIA analytic sensitivity, significant positive (P < or = .05) associations were detected with having written criteria for identifying unsatisfactory specimens and with having tested more than 10,000 specimens. For the 1989 overall EIA analytic performance, a significant negative (P < or = .05) association was found with using specific (Abbott) EIA materials, and a significant positive (P < or = .05) association was found with having tested more than 10,000 specimens. For Western blot results, the only significant (P < or = .05) associations were for both analytic sensitivity and overall analytic performance and having tested more than 10,000 specimens.

Blotting, Western↗

PubMed2026

Genetic Susceptibility to Incisional Hernia Evaluation of Hernia Polygenic Risk Scores.

OBJECTIVES: Incisional hernia (IH) affects 13-30% of people after abdominal surgery, resulting in substantial morbidity and costs. While clinical risk factors have been studied extensively, genomic risk for IH is incompletely understood. We aimed to evaluate the impact of polygenic risk scores (PRS) on IH risk prediction. METHODS: We created and evaluated three PRS for abdominal hernia, ventral hernia and latent hernia susceptibility for prediction of IH in an institutional biobank. The primary outcome was defined as the diagnosis or repair of an IH based on ICD-9/10-CM/PCS and CPT codes. Clinical covariates included age, sex, body mass index (BMI), smoking status, index procedure type, and perioperative surgical site infection. A phenome-wide association study (PheWAS) was performed to assess clinical associations with increased PRS. We then tested the ability of the PRS to improve prediction for IH by modeling clinical covariates with and without PRS in patients who underwent abdominal surgery. Model performance was assessed using 10 iterations of 5-fold cross-validation to estimate Brier scores and area under the receiver operating characteristic curve (AUROC), which were compared using cross-model Bayesian analysis of variance. RESULTS: In 55,809 subjects, assessed PRS was significantly associated with incisional, umbilical, and ventral hernia on PheWAS, with 1.19 greater odds of developing IH per 1-SD increase in PRS (95% CI: 1.13-1.25, P < 0.001). Of 9,909 subjects who underwent qualifying abdominal surgery, 706 developed IH. In this cohort, the latent hernia susceptibility PRS was associated with a 16% increased hazard of developing IH per 1-SD increase (HR 1.16; 95% CI: 1.07-1.26; P < 0.001). Compared to a predictive model using clinical covariates (Brier score = 0.047, 95% CI: 0.046-0.048; AUROC = 0.660, 95% CI: 0.653-0.666), addition of the PRS showed similar Brier score and AUROC estimates (Brier score = 0.047, 95% CI: 0.046-0.048; AUROC: 0.667, 95% CI: 0.661-0.673) at five years. Cross-model Bayesian analysis demonstrated >99% probability of practical equivalence when trying to detect a difference of ≥ 0.02. CONCLUSION: All three PRS for hernia were independently associated with IH, suggesting that genomic factors contribute significantly to IH development. However, none of the three PRS meaningfully improved clinical IH risk prediction in patients who underwent abdominal surgery. This suggests that clinical comorbidities and surgical techniques may be equally as important as genomic architecture.

Bayesian analysis↗

PubMed1991

Adequacy of a systems structure in the modeling of training effects on performance.

A systems model of training effects on performance was applied to eight initially untrained subjects who were volunteers for an endurance training program for the purpose of verifying the statistical adequacy of the systems structure. In the model initially proposed by T. W. Calvert, E. W. Banister, M. V. Savage, and T. Bach (IEEE Trans. Syst. Man Cybern. 6: 94-102, 1976), the performance changes were related to the successive training loads by three first-order transfer functions. In the present study, the number of first-order components was statistically tested. A model including only one component, which had a positive effect on the performance, provided a significant fit with the performances in every subject. A second component significantly improved the fit in only two subjects. This further component, which had a negative effect on performance, was identified as fatigue. Nevertheless, a two-antagonistic component model is proposed to provide a good representation of the training responses. However, the low level of exercise demands and the inaccuracy of the fit could have impaired the evidencing of a fatiguing effect during the presently studied training protocol.

Adult↗

PubMed1996

Change processes in a creation of meaning event.

Creation of meaning events are in-therapy change episodes that occur when a patient seeks to understand the meaning of an emotional experience. A performance model of this task was developed in an earlier study. The present study was conducted to determine which client performance components distinguish successful from unsuccessful creation of meaning episodes. Measures of referential activity were also applied to the events and uncovered important features of the therapist intervention that accompanied successful meaning making. The implications of these results for psychotherapy are discussed.

Adult↗

PubMed1981

The invariance of sentence performance structures across language modality.

Native users of American Sign Language were asked to manipulate sentences in four different ways: sign them at slow rate, parse them, make relatedness judgments of pairs of signs taken from each sentence, and recall the sentences. The data obtained from these four tasks (pause durations, parsing values, indices of relatedness and probe latencies) were used to construct hierarchical performance structures for each of the sentences. The resulting structures were highly similar across tasks; that is, performance structures are not task specific. The four measures at each sign boundary in each sentence were well predicted by a performance model, elaborated by Grosjean, Grosjean, and Lane for speech, that combines a parsing measure with a symmetry measure. Thus performance structures appear to be founded in the processing of language, be it visual or oral, and not in the properties of any particular communication modality.

Adult↗

PubMed2025

Examining Transcriptomic Markers Associated With Neutrophil Extracellular Traps to Predict Mortality Risk in Neonatal Sepsis.

BACKGROUND: Neonates are highly susceptible to sepsis, which is often accompanied by fatal coagulopathy. Anticoagulant therapies have not reduced sepsis-related mortality in clinical trials, possibly due to patient heterogeneity. Neutrophil extracellular traps (NETs) enhance coagulation by activating platelets, suggesting that NET-specific biomarkers may identify patients who may benefit from targeted anticoagulant treatment. This study evaluated the association between NET gene expression and adverse outcomes in neonatal sepsis. METHODS: We analyzed whole blood transcriptomes from 123 neonates with sepsis and developed a predictive model, the NET score, based on NET-related gene expression. Model performance was assessed in two independent validation sets. Mediation and correlation analyses explored the relationship between the NET score and a coagulation score. Temporal transcriptomic data from septic shock cases further tested this interaction. RESULTS: The NET score achieved AUCs of 88.7% and 85.4% in validation Sets 1 and 2, respectively, indicating strong predictive performance. Mediation and temporal analyses supported a sequential relationship between NETosis and coagulation in sepsis. Age-specificity of the model was confirmed using pediatric (n = 163) and adult (n = 86) sepsis transcriptomic datasets. Neonates with disseminated intravascular coagulation exhibited a trend toward elevated NET scores. CONCLUSIONS: Our findings support a novel risk stratification approach using the NET score to identify neonates at increased risk for sepsis-associated coagulopathy and poor outcomes, potentially guiding targeted therapeutic strategies.

neonatal sepsis↗

PubMed1998

A computational role for dopamine delivery in human decision-making.

Recent work suggests that fluctuations in dopamine delivery at target structures represent an evaluation of future events that can be used to direct learning and decision-making. To examine the behavioral consequences of this interpretation, we gave simple decision-making tasks to 66 human subjects and to a network based on a predictive model of mesencephalic dopamine systems. The human subjects displayed behavior similar to the network behavior in terms of choice allocation and the character of deliberation times. The agreement between human and model performances suggests a direct relationship between biases in human decision strategies and fluctuating dopamine delivery. We also show that the model offers a new interpretation of deficits that result when dopamine levels are increased or decreased through disease or pharmacological interventions. The bottom-up approach presented here also suggests that a variety of behavioral strategies may result from the expression of relatively simple neural mechanisms in different behavioral contexts.

Cerebral Cortex↗

PubMed1992

Monte Carlo modelling of the performance of a rotating slit-collimator for improved planar gamma-camera imaging.

Planar imaging with a gamma camera is currently limited by the performance of the collimator. Spatial resolution and sensitivity trade off against each other; it is not possible with conventional parallel-hole collimation to have high geometric sensitivity and at the same time excellent spatial resolution unless field-of-view is sacrificed by using fan- or cone-beam collimators. We propose a rotating slit-collimator which collects one-dimensional projections from which the planar image may be reconstructed by the theory of computed tomography. The performance of such a collimator is modelled by Monte Carlo methods and images are reconstructed by a convolution and backprojection technique. The performance is compared with that of a conventional parallel-hole collimator and it is shown that higher spatial resolution with increased sensitivity is possible with the slit-collimator. For a point source a spatial resolution of some 6 mm at a distance of 100 mm from the collimator with a x7 sensitivity compared with a parallel-hole collimator was achieved. Applications to bone scintigraphy are modelled and an improved performance in hot-spot imaging is demonstrated. The expected performance in cold-spot imaging is analytically investigated. The slit-collimator is not expected to improve cold-spot imaging. Practical design considerations are discussed.

Equipment Design↗

PubMed1992

Assessment of a model for overall left ventricular three-dimensional motion from MRI data.

In this paper we present a complete methodology to evaluate a model for overall three-dimensional (3D) motion of the human left ventricle (LV) from MRI data. The left ventricular motion is approximated by a linear model associated with an affine transformation to determine parameters for non-rigid motion of the LV. The proposed method has been applied to a normal patient and to a patient with cardiac disease. Results obtained show that the linear model provides a fairly good approximation of normal left ventricular motion, whereas serious cardiac disease produces abnormal motion, yielding altered model performances.

Heart Diseases↗

PubMed1995

Statistical response models for ozone exposure: their generality when applied to human spirometric and animal permeability functions of the lung.

Exposure of humans or animals to ozone (O3) alters spirometric and permeability functions of the lung. While these responses show clear concentration (C) dependency, the interactive role of exposure duration (T) has not been well defined. Ozone-induced alterations in forced expiratory volume in 1 s (FEV1) obtained from human studies and in levels of bronchoalveolar lavage fluid protein (BALP) obtained from studies of rats and guinea pigs were used to compare the utility of several proposed response models as functions of C and T. A large human-study database compiled for T = 2 h and a wide-ranging C and T study on animals were used to contrast each model. The models examined included the quadratic, logistic, log regression, and exponential models. This work suggests that models used for risk assessment should incorporate both T and C. Our results suggest that modified forms of many of these models perform well with both human and animal responses and can be additionally modified to include ventilation rate. As a simple biological model, the exponential model showed advantages. The absolute concentration rates-of-change in the exponential function of integrated physiological changes like BALP and FEV1 were equal for low O3 exposure.

Animals↗

PubMed1994

The identification of Class III malocclusions by discriminant analysis.

Lateral cephalometric radiographs of 210 control and 285 Class III subjects were traced, digitized, and 43 calculated variables submitted to a stepwise discriminant analysis. A 10-factor model was generated, giving 95.2 per cent correct classification of the control children and 95.1 per cent accurate identification of the Class III group. Ten control and 14 Class III children were categorized incorrectly. To test the validity of the analysis, radiographs of these 24 individuals were examined in detail. In all cases, a satisfactory reason for the misgrouping was identified. This investigation underlined the importance of rigorous standards of case selection when compiling the groups. The robustness of the 10-factor model was also examined. Subjects were arbitrarily split into two groups, the odd- and the even-numbered cases, and the discriminant analysis repeated on each. Both new models contained the same 10 variables, but with slightly different values for their accompanying coefficients. The cases erroneously identified by the whole group analysis were again misclassified, together with a few additional cases. Each new model performed equally well on the data from the opposing group as on that from which it had been derived. Thus, the model generated in this study was both valid and acceptably robust. It would therefore appear that discriminant analysis may be a viable tool in the identification and classification of groups of individuals.

Adolescent↗

PubMed1997

Development and prospective validation of a clinical index to predict survival in ambulatory patients referred for cardiac transplant evaluation.

BACKGROUND: Risk stratification of patients with end-stage congestive heart failure is a critical component of the transplant candidate selection process. Accurate identification of individuals most likely to survive without a transplant would facilitate more efficient use of scarce donor organs. METHODS AND RESULTS: Multivariable proportional hazards survival models were developed with the use of data on 80 clinical characteristics from 268 ambulatory patients with advanced heart failure (derivation sample). Invasive and noninvasive models (with and without catheterization-derived data) were constructed. A prognostic score was determined for each patient from each model. Stratum-specific likelihood ratios were used to develop three prognostic-score risk groups. The models were prospectively validated on 199 similar patients (validation sample) by calculation of the area under the receiver operating characteristic curve for 1-year event-free survival, the censored c-index for event-free survival, and comparison of event-free survival curves for prognostic-score risk strata. Outcome events were defined as urgent transplant or death without transplant. The noninvasive model performed well in both samples, and increased performance was not attained by the addition of catheterization-derived variables. Prognostic-score risk groups derived from the noninvasive model in the derivation sample effectively stratified the risk of an outcome event in both samples (1-year event-free survival for derivation and validation samples, respectively: low risk, 93% and 88%; medium risk, 72% and 60%; high risk, 43% and 35%). CONCLUSIONS: Selection of candidates for cardiac transplantation may be improved by use of this noninvasive risk-stratification model.

Cardiac Output, Low↗

PubMed1995

Predicting future functional status for seriously ill hospitalized adults. The SUPPORT prognostic model.

OBJECTIVE: To develop a model estimating the probability of an adult patient having severe functional limitations 2 months after being hospitalized with one of nine serious illnesses. DESIGN: Prospective cohort study. SETTING: Five teaching hospitals in the United States. PARTICIPANTS: 1746 patients (model development) who survived 2 months and completed an interview, selected from 4301 patients in the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT); independent validation sample of 2478 patients. MEASUREMENTS AND MAIN OUTCOMES: Patient function 2 months after admission categorized as absence or presence of severe functional limitations (defined as Sickness Impact Profile scores > or = 30 or as activities of daily living scores > or = 4 [levels that require near-constant personal assistance]). A logistic regression model was constructed to predict severe functional limitation. RESULTS: One third (n = 590) of patients who were interviewed at 2 months had severe functional limitations. Changes in functional status were common: Of those with no baseline dependencies (not dependent on personal assistance), 21% were severely limited at 2 months; of those with 4 or more baseline limitations, 30% had improved. The patient's ability to do activities of daily living was the most important predictor of functional status. Physiologic abnormalities, diagnosis, days in hospital, age, quality of life, and previous exercise capacity also contributed substantially. Model performance, assessed using receiver-operating characteristic curves, was 0.79 for the development sample and 0.75 for the validation sample. The model was well calibrated for the entire risk range. CONCLUSIONS: Functional outcome varied substantially after hospitalization for a serious illness. A small amount of readily available clinical information can estimate the probability of severe functional limitations.

Activities of Daily Living↗

PubMed1987

Collicular ensemble coding of saccades based on vector summation.

The superior colliculus in the monkey contains a topographically organized representation of the target in its upper layers and saccade-related activity in its deeper layers. Since collicular movement fields are quite large, a considerable region of the colliculus is active whenever a saccade is made. We have modelled the collicular role in saccade generation based on the idea, proposed earlier in the literature, that each movement cell causes a movement tendency in the direction of the external world point which it represents in the collicular map. The model is organized as follows: An anisotropic logarithmic mapping transforms retinal coordinates into collicular coordinates. A two-dimensional Gaussian function describes the spatial extent of the movement-related activity in the deeper layers. An efferent mapping function specifies how the direction and the size of the movement contribution of each colliculus neuron depends on its location and its firing rate. The total saccade is the vector sum of the individual cell contributions. This very simple model (seven fixed parameters) has been used to simulate metrical properties of saccades: in response to visual targets; in response to electrical stimulation in one colliculus, and after a colliculus lesion. Model performance appears to be remarkably realistic but cannot account for some border effects and responses to double stimulation. Suggestions on how the model can be improved and extended will be presented.

Brain Mapping↗

PubMed1975

Cost-performance analysis of cataloging and card production in a medical center library.

The unit cost of cataloging current English language monographs was studies and compared with the cost of purchasing catalog cards from a commercial source. Two hypotheses were proposed: (1) in-library costs for cataloging and card production are higher than those for the purchased-card method; (2) throughput time is faster for the in-library method. In addition, the data can be used to develop an analytical cost-performance model for administrative purposes. The data presented support the hypotheses. The model developed provides a mechanism for arriving at a cost for different levels of service and can be used to measure the performance of other alternative methods of cataloging. Implications for the use of CATLINE are discussed and suggestions for further studies are described.

Cataloging↗

PubMed1997

Lateralized spatial strategies in oscillating drawing movements.

Kinematic characteristics and lateral differences between two upper extremities were investigated in a unimanual graphic task involving fast and precise oscillating movements on the vertical plane. The spatial locations of sequential reversal points were used to calculate the pairs of angles, relative to the horizontal axis. The point biserial coefficient of correlation was used to analyze the difference between big and large angles and their sequence in each pair. Three main groups (A, B, and C) of performance models were distinguished in 132 tests by 33 strongly right-handed male subjects. Group A showed strong variation in vertical movement, Group B covariation in vertical and horizontal vectors, while Group C reflected independent variation of both vertical and horizontal directions. It is suggested that the movement strategies might reflect three different models of motor control involving coupling of an oscillator controlling pools of motoneurons which regulates horizontal movements with an oscillator controlling vertical movement (Groups A + B) or with nonoscillating control signal (Group B). It is argued that Group A represents the simplest strategy and only performance Type A met by the left hand.

Adult↗

PubMed2025

Opportunities for machine learning to predict cross-neutralization in FMDV serotype O.

Accurately estimating cross-neutralization between serotype O foot-and-mouth disease viruses (FMDVs) is critical for guiding vaccine selection and disease management. In this study, we developed a machine learning approach to estimate r1 values-an established measure of antigenic similarity-using VP1 sequence data and published virus neutralization titer (VNT) results. Our dataset comprised 108 serum-virus pairs representing 73 distinct FMDV strains. We applied Boruta feature selection and random forest classifiers, optimizing model performance through tenfold cross-validation and sub-sampling to address class imbalance. Predictors included pairwise amino acid distances, site-specific polymorphisms, and differences in potential N-glycosylation sites. Using a 0.3 r1 threshold to define cross-neutralization, the final model achieved high accuracy (0.96), sensitivity (0.93), and specificity (0.96) in training, and performed robustly on independent test sets - accuracy was 0.75 (95% CI 0.60 and 0.90), F1 score 0.86% and PPV 0.77. Importantly, key VP1 residues-positions 48, 100, 135, 150, and 151-emerged as strong predictors of antigenic relationships. Our results demonstrate the utility of integrating routinely generated genomic data with machine learning to inform vaccine candidate selection and anticipate immune interactions among circulating FMDV strains. This approach offers a practical tool for accelerating vaccine decision-making and can be adapted to other FMDV serotypes. The latest version of the r1 predictive model is available for access via a Shiny dashboard (https://dmakau.shinyapps.io/PredImmune-FMD/).

Foot-and-Mouth Disease Virus↗

PubMed1998

Time series forecasts of ambulance run volume.

To test the hypothesis that time series analysis can provide accurate predictions of future ambulance service run volume, a prospective stochastic time series modeling study was conducted at a community-based regional ambulance service. For all requests for ambulance transport during two sequential years, the time and date, total run time, and acuity code of the run were recorded in a computer database. Time series variables were formed for ambulance service runs per hour, total run time, and acuity. Prediction models were developed from one complete year's data (1994) and included four model types: raw observations, moving average, means with moving average smoothing, and autoregressive integrated moving average. Forecasts from each model were tested against observations from the first 24 weeks of the subsequent year (1995). Each model's adequacy was tested on residuals by autocorrelation functions, integrated periodograms, linear regression, and differences among the variances. A total of 68,433 patients were seen in 1994 and 32,783 in the first 24 weeks of 1995. Large periodic variations in run volume with time of day were found (P < .001). A model based on arithmetic means of each hour of the week with 3-point moving average smoothing yielded the most accurate forecasts and explained 54.3% of the variation observed in the 1995 test series (P < .001). Time series analysis can provide powerful, accurate short-range forecasts of future ambulance service run volume. Simpler, less expensive models performed best in this study.

Ambulances↗