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PubMed1979

A mathematical model of speedskating performance improvement for goal setting and program evaluation.

An analysis of world class performance improvement over chronological time was used to develop mathematical curves of performance for each speedskating event. The equations were calculated using an unconstrained non-linear least squares iterative curve-fitting technique. A non-linear model was selected to satisfy the principle of diminishing returns, that is, it is more difficult to achieve a unit of performance improvement as performance approaches the theoretical limits of man. Minimum criteria of acceptance for each curve were: 1) the coefficient of determination must be 0.90; 2) the year 2000 predicted value must be less than the current world record; and 3) the curve must be progressive, i.e. satisfy the principle of diminishing returns. Satisfactory curves were calculated for seven of the eight male and female events studied. A four year Olympic cycle was noted and a definite change in performance trend was identified as occurring in the mid 1960's. The calculated mathematical curves can be used in three applications: 1) setting objective individual goals and evaluating these goals; 2) evaluating and comparing training programs on successive years; and 3) evaluating total programs.

Female↗
PubMed2003

A personality trait-based interactionist model of job performance.

Evidence for situational specificity of personality-job performance relations calls for better understanding of how personality is expressed as valued work behavior. On the basis of an interactionist principle of trait activation (R. P. Tett & H. A. Guterman, 2000), a model is proposed that distinguishes among 5 situational features relevant to trait expression (job demands, distracters, constraints, releasers, and facilitators), operating at task, social, and organizational levels. Trait-expressive work behavior is distinguished from (valued) job performance in clarifying the conditions favoring personality use in selection efforts. The model frames linkages between situational taxonomies (e.g., J. L. Holland's [1985] RIASEC model) and the Big Five and promotes useful discussion of critical issues, including situational specificity, personality-oriented job analysis, team building, and work motivation.

Aptitude↗
PubMed1999

Performance: a multi-disciplinary and conceptual model.

We contend that the scientific study of performance requires a model or paradigm. We propose a performance model with an underlying mathematical basis that is well defined, has explicit assumptions and has the potential to be both heuristic and scientifically testable. The model is based on an integration of concepts from health sciences and psychology that have been adapted to performance measurement in health care. The proposed performance model consists of a combination of four primary elements: quality of care, cost of care, access to care and satisfaction. Satisfaction is defined as a function of perceived and expected outcomes of care and perceived and expected input. This performance model can serve as both a tool for understanding and as a vehicle for comparing performance within and between health care organizations. We believe that this model can be used to develop a performance profile report and the future report card.

Delivery of Health Care↗
PubMed2005

Clinically and mammographically occult breast lesions on MR images: potential effect of computerized assessment on clinical reading.

PURPOSE: To investigate if and how computerized analysis complements characterization of breast lesions with clinical reading at magnetic resonance imaging. MATERIALS AND METHODS: The institutional review board approved the use of data obtained prospectively and analyzed either prospectively with informed patient consent or retrospectively with waiver of consent. An existing computerized analysis system was retrained with 100 breast lesions (in 78 patients with mean age of 46.5 years) and tested with 136 other lesions (in 113 patients with mean age of 48.9 years; P=.15 for age difference between groups). Seventy-five lesions in the training set were previously rated by one of three radiologists in daily clinical practice. Lesion rating (as benign, probably benign, indeterminate, suspicious, or highly suggestive of malignancy) and probability of malignancy calculated with computerized analysis were included as covariates in logistic regression analysis to obtain a combined model. The performance of the model was compared with that of clinical reading alone in a set of 72 clinically and mammographically occult lesions not used to train the computerized analysis system (in 60 patients with mean age of 43.5 years; P=.09 for age difference between training and testing groups). Receiver operating characteristic (ROC) curves were plotted, and areas under the ROC curves were calculated and compared. RESULTS: Performance of reading in the clinical setting, as indicated by area under the ROC curve (Az=0.86), was similar to that of computerized analysis (Az=0.85; P=.99). Significant overall improvement in performance was obtained with the combined model (Az=0.91; P=.03). Improvement was accomplished mostly in characterization of lesions rated indeterminate or suspicious by radiologists. CONCLUSION: Computerized analysis complements clinical reading and makes computer-aided diagnosis feasible. The complementary information has the potential to increase overall performance for clinically and mammographically occult lesions.

Breast Neoplasms↗
PubMed2006

Comparison in a laboratory model between the performance of a urinary closed system bag with double non-return valve and that of a single valve system.

BACKGROUND: Catheter-associated urinary tract infection is the most common nosocomial infection in clinical settings. For bacteria ascending to the bladder the most common route is the extraluminal, but the intraluminal route also plays a role. For this reason, we compared two urinary closed system bags (CSB), one with a double and the other with a single non-return valve (NRV), in a laboratory setting in order to establish their ability to prevent or delay the ascent of bacteria from the drainage bag to the bladder. PATIENTS AND METHODS: The tests were performed in two microbiological laboratories (Copenhagen (C), Denmark and Freiburg (F), Germany). These were blinded to each other. A urinary tract model using artificial urine was set up. Two sets of ten drainage bags each with a double NRV (CSB A), and two sets of ten drainage bags each with a single NRV (CSB B) were inoculated with Escherichia coli (F: ATCC 25922; C: clinical strain). Daily samples were taken from two drainage ports on each system - one above the NRV (Port I), the other above the top of the artificial bladder (Port II). Time till E. coli was detected at the drainage ports (time to positivity) was measured. Colonization of the 'bladder' was defined as time to positivity at Port II. RESULTS: No significant differences in time to positivity at Port I (median 9.0, range: 6-12 for CSB B vs median 9.5 days, range: 6-13 for CSB A) were observed between the two systems. However, substantial differences were seen between the two systems in time to positivity at Port II: Port II on the bladder model using CSB B became positive after a median of 14.0 days (range: 10-22), whereas Port II of the model using CSB A only became positive after 21.5 days (range: 13-24). This amounts to a highly significant difference of 7.5 days (p = 0.0001) in the mean. CONCLUSION: Under laboratory conditions, colonization of the 'bladder' was significantly delayed when the CSB with a double NRV was used in comparison to the results obtained from the single NRV-system. Clinical trials should be conducted to investigate whether the urinary CSB with the double NRV has the ability to prevent (or to delay the onset of) catheter-associated urinary tract infection.

Equipment Contamination↗
PubMed2004

Prediction of phenanthrene uptake by plants with a partition-limited model.

The performance of a partition-limited model on prediction of phenanthrene uptake by a wide variety of plant species was evaluated using a greenhouse study. The model predictions of root or shoot concentrations for tested plant species were all within an order of magnitude of the observed values. Modeled root concentrations appeared to be more accurate than modeled shoot concentrations. The differences of simulated and experimented concentrations of phenanthrene in roots and shoots of three representative plant species, including ryegrass, flowering Chinese cabbage, and three-colored amaranth, were less than 81% for roots and 103% for shoots. Results are promising in that the alpha(pt) values of the partition-limited model for root uptake of phenanthrene correlate well with root lipid contents. Additionally, a significantly positive correlation is also observed between root concentration factors (RCFs, defined as the ratio of contaminant concentrations in root and in soil on a dry weight basis) of phenanthrene and root lipid contents. Results from this study suggest that the partition-limited model may have potential applications for predicting the plant PAH concentration in contaminated sites.

Biodegradation, Environmental↗
PubMed1999

Numerical test of the damping time of layer-by-layer growth on stochastic models.

We perform Monte Carlo simulations on stochastic models such as the Wolf-Villain (WV) model and the Family model in a modified version to measure the mean separation l between islands in a submonolayer regime and the damping time t* of layer-by-layer growth oscillations in one dimension. The stochastic models are modified, allowing for diffusion within interval r upon deposition. It is found numerically that the mean separation and the damping time depend on the diffusion interval r, leading to the fact that the damping time is related to the mean separation as t* approximately l(4/3) for the WV model and t* approximately l(2) for the Family model. The numerical results are in excellent agreement with recent theoretical predictions.

Journal Article↗
PubMed2002

Development of a rat model of sexual performance anxiety: effect of behavioural and pharmacological hyperadrenergic stimulation on APO-induced erections.

As part of the multifactorial nature of erectile dysfunction, anxiety associated with sexual performance (SPA) remains a major contributing factor to its progression. In fact, the heightened sympathetic activity associated with sexual performance anxiety may be a key early component of this disruption of normal erectile responses. We are not aware that any animal models have been developed to assess this phenomenon. Using apomorphine (APO, 80 microg/kg s.c.)-induced erections in rats we characterised the effects of behavioural or pharmacological hyperadrenergic stimulation (that is, anxiety) on erections and hemodynamics. We developed an experimental SPA paradigm by exposing male rats to the stress of being observed by a larger, older male rat placed in close proximity to test rats during APO testing. In a separate group, adrenergic stress was simulated using a sympathomimetic, methoxamine (MXA) given prior to APO testing. In a third group, the changes in circulatory parameters (mean arterial pressure, heart rate) were determined following instrumentation with radiotelemetric transducers for each scenario. APO-induced erections were significantly lower in both the behavioural (1.25+/-0.8) and pharmacological (0.33+/-0.5) stressor paradigms compared to controls (2.81+/-0.9). Further, erections in MXA-treated rats were significantly lower than in the observed scenario. Despite the differences in erections hemodynamic assessments showed no differences in MAP or HR changes between the different experimental conditions. Thus, both the behavioural and pharmacological paradigms of SPA decreased erections, but did not affect the circulation. This suggests that the level of hyperadrenergic input required to induce erectile dysfunction can be subtle, and target only erectogenic pathways.

Animals↗
PubMed2003

The 5-HT 1A receptor antagonist WAY 100635 improves rats performance in different models of amnesia evaluated by the object recognition task.

The effects of the 5-HT(1A) receptor antagonist WAY 100635 on recognition memory were investigated in two different amnestic models in the rat by using the object recognition task. WAY 100635 at 1 mg/kg, but not at 0.3 mg/kg, counteracted scopolamine-induced performance deficits in the acquisition version of this behavioral paradigm. At the same dose, WAY 100635 antagonized extinction of recognition memory in the normal rat, suggesting that it affected acquisition, storage and retrieval of information. These results support and extend prior findings that interactions between the serotonergic and cholinergic systems are relevant to cognition and indicate that WAY 100635 modulates different aspects of recognition memory.

Amnesia↗
PubMed1991

A catastrophe model of anxiety and performance.

An experiment is reported which tests Fazey & Hardy's (1988) catastrophe model of anxiety and performance. Eight experienced basketball players were required to perform a set shooting task, under conditions of high and low cognitive anxiety. On each of these occasions, physiological arousal was manipulated by means of physical work in such a way that subjects were tested with physiological arousal increasing and decreasing. Curve-fitting procedures followed by non-parametric tests of significance confirmed (p less than .002) Fazey & Hardy's hysteresis hypothesis: namely, that the polynomial curves for the increasing vs. decreasing arousal conditions would be horizontally displaced relative to each other in the high cognitive anxiety condition, but superimposed on top of one another in the low cognitive anxiety condition. Other non-parametric procedures showed that subjects' maximum performances were higher, their minimum performances lower, and their critical decrements in performance greater in the high cognitive anxiety condition than in the low cognitive anxiety condition. These results were taken as strong support for Fazey & Hardy's catastrophe model of anxiety and performance. The implications of the model for current theorizing on the anxiety-performance relationship are also discussed.

Achievement↗
PubMed2001

Modeling colloid transport for performance assessment.

The natural system is expected to contribute to isolation at the proposed high-level nuclear waste (HLW) geologic repository at Yucca Mountain, NV (YM). In developing performance assessment (PA) computer models to simulate long-term behavior at YM, colloidal transport of radionuclides has been proposed as a critical factor because of the possible reduced interaction with the geologic media. Site-specific information on the chemistry and natural colloid concentration of saturated zone groundwaters in the vicinity of YM is combined with a surface complexation sorption model to evaluate the impact of natural colloids on calculated retardation factors (RF) for several radioelements of concern in PA. Inclusion of colloids into the conceptual model can reduce the calculated effective retardation significantly. Strongly sorbed radionuclides such as americium and thorium are most affected by pseudocolloid formation and transport, with a potential reduction in RF of several orders of magnitude. Radioelements that are less strongly sorbed under YM conditions, such as uranium and neptunium, are not affected significantly by colloid transport, and transport of plutonium in the valence state is only moderately enhanced. Model results showed no increase in the peak mean annual total effective dose equivalent (TEDE) within a compliance period of 10,000 years, although this is strongly dependent on container life in the base case scenario. At longer times, simulated container failures increase and the TEDE from the colloidal models increased by a factor of 60 from the base case. By using mechanistic models and sensitivity analyses to determine what parameters and transport processes affect the TEDE, colloidal transport in future versions of the TPA code can be represented more accurately.

Adsorption↗
PubMed1994

Electromechanical transduction: reduction-driven hydrophobic folding demonstrated in a model protein to perform mechanical work.

It has long been appreciated that hydrophobic folding is an important element of protein structure formation. Here it is demonstrated for the first time that the electrochemical or chemical reduction of a nicotinamide in a model protein, which increases hydrophobicity, can drive hydrophobic folding and assembly in such a way as to lift a weight or otherwise contract against a constant tensional force. The model protein, poly[0.73(GVGVP),0.27(GK(NMeN)GVP], can be gamma-irradiation cross-linked to form an elastic matrix which contracts on raising the temperature from below to above the transition range for hydrophobic folding and assembly. On reduction of the N-methyl nicotinamide, (NMeN), the transition temperature range is lowered from above to below 20 degrees C to drive contraction due to hydrophobic folding with the performance of mechanical work.

Amino Acid Sequence↗
PubMed1997

Impact of a function-based payment model on the financial performance of acute inpatient medical rehabilitation providers: a simulation analysis.

OBJECTIVES: To operationalize research findings about a medical rehabilitation classification and payment model by building a prototype of a prospective payment system, and to determine whether this prototype model promotes payment equity. This latter objective is accomplished by identifying whether any facility or payment model characteristics are systematically associated with financial performance. DESIGN: This study was conducted in two phases. In Phase 1 the components of a diagnosis-related group (DRG)-like payment system, including a base rate, function-related group (FRG) weights, and adjusters, were identified and estimated using hospital cost functions. Phase 2 consisted of a simulation analysis in which each facility's financial performance was modeled, based on its 1990-1991 case mix. A multivariate regression equation was conducted to assess the extent to which characteristics of 42 rehabilitation facilities contribute toward determining financial performance under the present Medicare payment system as well as under the hypothetical model developed. PARTICIPANTS: Phase 1 (model development) included 61 rehabilitation hospitals. Approximately 59% were rehabilitation units within a general hospital and 48% were teaching facilities. The number of rehabilitation beds averaged 52. Phase 2 of the stimulation analysis included 42 rehabilitation facilities, subscribers to UDS in 1990-1991. Of these, 69% were rehabilitation units and 52% were teaching facilities. The number of rehabilitation beds averaged 48. MAIN OUTCOME MEASURE: Financial performance, as measured by the ratio of reimbursement to average costs. RESULTS: Case-mix index is the primary determinant of financial performance under the present Medicare payment system. None of the facility characteristics included in this analysis were associated with financial performance under the hypothetical FRG payment model. CONCLUSIONS: The most notable impact of an FRG-based payment model would be to create a stronger link between resource intensity and level of reimbursement, resulting in greater equity in the reimbursement of inpatient medical rehabilitation hospitals.

Health Services Research↗
PubMed1999

Interchangeability and predictive performance of empirical tolerance models.

Models of tolerance are commonly derived on empirical grounds, because of lack of knowledge about the mechanism of tolerance or because of the difficulty of appropriately simplifying complex physiological processes. The present study was performed to evaluate the interchangeability of tolerance models used in the literature and to address some determinants for selection of an appropriate design and data analysis strategy. Seven models were chosen (noncompetitive antagonist model, partial agonist model, reverse agonist model, direct moderator model, indirect moderator model, pool model and adaptive pool model) along with their corresponding parameter estimates, representing a wide range of empirical models. The performance of the models on various data sets was evaluated. Data were simulated from each original model and were further analysed by the other models. The effect-time course of each and every data set could be described well by at least 2 different empirical tolerance models, but no model could describe all the data sets adequately. However, all models could adequately describe at least 2 different data sets. This indicates that, without additional knowledge or assumptions, it is unlikely that reliable mechanistic information can be deduced from the mere fact that 1 (or more) of these models can describe the data. Generally, data expressing only limited tolerance can be described by a wide variety of models, whereas few models will be appropriate for data characterised by extensive tolerance. The models that gave an adequate description of a data set were selected for further study that investigated their predictive capacity based on the parameters previously determined. Predictions were made for 4 different administration schemes. The selected models gave similar predictions for the extended designs of 3 data sets for which the original study designs characterised tolerance well. For the other 4 data sets, the selected models gave disparate predictions, although the models described the original data set well. Thus, the predictive capability of a model was linked to the original study design, whereas the correlation between predictive performance and the type of model was weak or absent. Based on the results, factors of importance for the design and evaluation of studies of tolerance were identified and discussed.

Animals↗
PubMed2004

Effect of articulatory suppression on task-switching performance: implications for models of working memory.

In a series of experiments, we examine some effects of articulatory suppression in task switching. The results from Experiments 1a and 2a showed that switch costs in the articulatory suppression condition were larger than those in the control and tapping conditions when the switching cues were not provided. On the other hand, articulatory suppression did not have any effect on switch costs in Experiments 1b and 2b, where the switching cues were provided. In Experiment 3, using a computer-assisted experimentation, this pattern of data was replicated in a two-factor design with articulatory suppression and switching cues factors. The results indicate that a specific component in working memory, the phonological loop, might contribute to the performance in task switching, at least in situations where the external task cues were not available. The data reported here suggest that the phonological loop plays an important role in one of the executive control processes, and challenge the traditional idea that the slave systems are simply governed by the central executive in the working memory.

Adolescent↗