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A literature-based model of the determinants of the accuracy of performance ratings is presented. The model indicates that the major determinants of accuracy are: (a) rater motivation; (b) rater ability; and (c) availability of appropriate judgmental norms. Several propositions and suggestions for further research are derived from the components of the model.
This Project evaluated a human visual system model (JNDmetrix) based on just noticeable difference (JND) and frequency-channel vision-modeling principles to assess whether a Cathode ray tube (CRT) or a liquid crystal display (LCD) monochrome display monitor would yield better observer performance in radiographic interpretation. Key physical characteristics, such as veiling glare and modulation transfer function (MTF) of the CRT and LCD were measured. Regions of interest from mammographic images with masses of different contrast levels were shown once on each display to six radiologists using a counterbalanced presentation order. The images were analyzed using the JNDmetrix model. Performance as measured by receiver operating characteristic (ROC) analysis was significantly better overall on the LCD display (P = 0.0120). The JNDmetrix model predicted the result (P = 0.0046) and correlation between human and computer observers was high (r (2) (quadratic) = 0.997). The results suggest that observer performance with LCD displays is superior to CRT viewing, at least for on-axis viewing.
Transitive performance (TP) is a learning-based behaviour exhibited by a wide range of species, where if a subject has been taught to prefer A when presented with the pair AB but to prefer B when presented with the pair BC, then the subject will also prefer A when presented with the novel pair AC. Most explanations of TP assume that subjects recognize and learn an underlying sequence from observing the training pairs. However, data from squirrel monkeys (Saimiri sciureus) and young children contradict this, showing that when three different items (a triad) are drawn from the sequence, subjects' performance degrades systematically (McGonigle and Chalmers, Nature 267:694-696, 1977; Chalmers and McGonigle, Journal of Experimental Child Psychology 37:355-377, 1984; Harris and McGonigle, The Quarterly Journal of Experimental Psychology 47B:319-348, 1994). We present here the two-tier model, the first learning model of TP which accounts for this systematic performance degradation. Our model assumes primate TP is based on a general-purpose task learning system rather than a special-purpose sequence-learning system. It supports the hypothesis of Heckers et al. (Hippocampus 14:153-162, 2004) that TP is an expression of two separate general learning elements: one for associating actions and contexts, another for prioritising associations when more than one context is present. The two-tier model also provides explanations for why phased training is important for helping subjects learn the initial training pairs and why some subjects fail to do so. It also supports the Harris and McGonigle (The Quarterly Journal of Experimental Psychology 47B:319-348, 1994) explanation of why, once the training pairs have been acquired, subjects perform transitive choice automatically on two-item diads, but not when exposed to triads from the same sequence.
The Joint Commission on Accreditation of Healthcare Organizations has attempted to move away from simple measures of organizational process to measures of organizational performance. As no measures of organizational performance existed, the Joint Commission was forced to embark upon a lengthy search for methodologies and technologies to measure organizational performance. In addition, an approach to the use of performance measures, which would be acceptable to the health service community, and which was compatible with the process of accreditation, had to be found.
PURPOSE: The aims of the study were to assess the degree of accuracy of model surgery performed manually using the Eastman technique and to compare it with model surgery performed with the aid of a robot arm. PATIENTS AND METHODS: Twenty-one patients undergoing orthognathic surgery gave consent for this study. They were divided into 2 groups based on the model surgery technique used. Group A (52%) had model surgery performed manually, whereas group B (48%) had their model surgery performed using the robot arm. Patients' maxillary casts were measured before and after model surgery, and results were compared with those for the original treatment plan in horizontal (x-axis), vertical (y-axis), and transverse (z-axis) planes. RESULTS: Statistical analysis using Mann-Whitney U test for x- and y-axis and independent sample t test for z-axis have shown significant differences between both groups in x-axis (P =.024) and y-axis (P =.01) but not in z-axis (P =.776). CONCLUSIONS: Model surgery performed with the aid of a robot arm is significantly more accurate in anteroposterior and vertical planes than is manual model surgery. Robot arm has an important role to play in orthognathic surgery planning and in determining the biometrics of orthognathic surgical change at the model surgery stage.
We have developed an immunization procedure for the production of effective anti-beta-amyloid (anti-Abeta) antibodies, using filamentous phage displaying only 4 amino acids. The EFRH sequence, encompassing amino acids 3-6 of the 42 residues of Abeta peptide, was found previously to be the main regulatory site for amyloid modulation and the epitope of anti-aggregating antibodies. Engineered filamentous phage enable the display of various numbers of EFRH copies on the phage and serve as potent carriers of antigens. In the present study we have found that phage displaying high EFRH copy number are effective in eliciting humoral response against the EFRH sequence, which in turn relieves the amyloid burden in the brains of amyloid precursor protein Tg mice and improves their ability to perform cognitive tasks.
Most computational models for gender classification use global information (the full face image) giving equal weight to the whole face area irrespective of the importance of the internal features. Here, we use a global and feature based representation of face images that includes both global and featural information. We use dimensionality reduction techniques and a support vector machine classifier and show that this method performs better than either global or feature based representations alone. We also present results of human subjects performance on gender classification task and evaluate how the different dimensionality reduction techniques compare with human subjects performance. The results support the psychological plausibility of the global and feature based representation.
Biofilter, dynamic modeling software characterizing contaminant removal via biofiltration, was used in the preliminary design of a biofilter to treat odorous hydrogen sulfide (H2S). Steady-state model simulations were run to generate performance plots for various influent concentrations, loadings, residence times, media sizes, and temperatures. Although elimination capacity and removal efficiency frequently are used to characterize biofilter performance, effluent concentration can be used to characterize performance when treating to a target effluent concentration. Model simulations illustrate that, at a given temperature, a biofilter cannot reduce H2S emissions below a minimum value, no matter how large the biofilter or how long the residence time. However, a higher biofilter temperature results in lower effluent H2S concentrations. Because dynamic model simulations show that shock loading can significantly increase the effluent concentration above values predicted by the steady-state model simulations, it is recommended that, to consistently meet treatment objectives, dynamic feed conditions should be considered. This study illustrates that modeling can serve as a valuable tool in the design and performance optimization of biofilters.
STUDY OBJECTIVE: Evaluation of the performance of the APACHE (acute physiology and chronic health evaluation) III ICU and hospital mortality models at an Australian tertiary adult ICU. DESIGN: Noninterventional, observational study. SETTING: Metropolitan, Australian, tertiary referral medical/surgical ICU. PATIENTS: A total of 3,398 consecutive eligible admissions from January 1, 1995, to December 31, 1997. MEASUREMENTS: Prospective collection of demographic, diagnostic, physiologic, laboratory, admission, and discharge data. RESULTS: The patient sample was younger and more commonly male, with more comorbidities and a different operative and referral source mix, compared to the APACHE III development sample. Receiver operating characteristic curve areas for ICU (0.92) and hospital mortality (0.90) demonstrated excellent discrimination. Observed ICU mortality (9.9%) did not significantly differ from the prediction of the APACHE III model (8.9%) or the APACHE III model adjusted for hospital characteristics (10.5%). The hospital mortality (16.0%) was underestimated by the APACHE III model [13.6%; chi(2)(1) = 7.4; p = 0.01]. With proprietary adjustments for hospital characteristics (14.9%) or referenced to the US database (15.6%), agreement was closer. Good calibration was found with all models except the unadjusted hospital mortality model. CONCLUSION: In contrast to other non-American studies, this Australian study demonstrates that the APACHE III can perform well on independent assessment. As perfect discrimination and calibration cannot coexist in a probabilistic model with dichotomous outcomes, performance of APACHE III models with proprietary adjustment for hospital characteristic provide a good compromise for use in quality surveillance.
Some of the effects of noise on the perception of plosive-vowel syllables have been investigated. It was found that noise added to the syllables for the duration of the speech had a more deleterious effect on perception than noise of the same intensity played continuously. Physiological experiments have shown that the response thresholds of cochlear nerve fibers to tones are raised by continuous background noise but not by short bursts of noise. It is suggested that this may be responsible for the speech perception results. In order to investigate this, an auditory model was developed which incorporated response threshold shifts. This was interfaced to a hidden Markov model recognizer and tested with the same sounds that were employed in the human perception experiments. The recognition scores were greater with the threshold shifts than without them.
This paper presents a case study in simulating leachate generation and transport at a 2000 ton/day landfill facility and assesses leachate migration away from the landfill in order to control associated environmental impacts, particularly on groundwater wells down gradient of the site. The site offers unique characteristics in that it is a former quarry converted to a landfill and is planned to have refuse depths that could reach 100 m, making it one of the deepest in the world. Leachate quantity and potential percolation into the subsurface are estimated using the Hydrologic Evaluation of Landfill Performance (HELP) model. A three-dimensional subsurface model (PORFLOW) was adopted to simulate ground water flow and contaminant transport away from the site. A comprehensive sensitivity analysis to leachate transport control parameters was also conducted. Sensitivity analysis suggests that changes in partition coefficient, source strength, aquifer hydraulic conductivity, and dispersivity have the most significant impact on model output indicating that these parameters should be carefully selected when similar modeling studies are performed.
Model-based elastography is fraught with problems owing to the ill-posed nature of the inverse elasticity problem. To overcome this limitation, we have recently developed a novel inversion scheme that incorporates a priori information concerning the mechanical properties of the underlying tissue structures, and the variance incurred during displacement estimation in the modulus image reconstruction process. The information was procured by employing standard strain imaging methodology, and introduced in the reconstruction process through the generalized Tikhonov approach. In this paper, we report the results of experiments conducted on gelatin phantoms to evaluate the performance of modulus elastograms computed with the generalized Tikhonov (GTK) estimation criterion relative to those computed by employing the un-weighted least-squares estimation criterion, the weighted least-squares estimation criterion and the standard Tikhonov method (i.e., the generalized Tikhonov method with no modulus prior). The results indicate that modulus elastograms computed with the generalized Tikhonov approach had superior elastographic contrast discrimination and contrast recovery. In addition, image reconstruction was more resilient to structural decorrelation noise when additional constraints were imposed on the reconstruction process through the GTK method.
OBJECTIVE: Determining prognosis is an important part of medical planning for long-term care residents. Clarifying the resident characteristics associated with increased mortality has received little attention from investigators, and many approaches that have been suggested are unsuitable for widespread use. Using a readily available database, we sought to determine factors associated with 1-year mortality in established long-term care residents. DESIGN: A retrospective cohort study. SETTING: A 725-bed long-term care facility. MEASUREMENTS: We examined Minimum Data Set (MDS) information on 780 residents from April 1994 through August 1997. The association between death and 65 resident factors, covering a broad array of physical, functional, medical, and psychosocial measures, was examined initially in bivariate proportional hazards models. Putative factors with P values < .10 in bivariate analysis were considered in the multivariate analysis. Using these factors, we employed a forward step-wise multivariate proportional hazards regression method to select the set of factors associated independently with mortality at a P value < .05. A mortality score was developed by assigning points to each factor based on the risk ratio in the multivariate proportional hazards model. The performance characteristics of the model were examined using logistic regression. RESULTS: Forty-four of the 65 factors examined were associated with 1-year mortality in bivariate proportional hazards analysis. Eight of these 44 factors were associated with 1-year mortality in the multivariate proportional hazards regression. These factors were functional impairment, weight loss, shortness of breath, male gender, low body mass index, swallowing problems, congestive heart failure, and advanced age. A higher mortality score was associated with a higher death rate in the subsequent year. The model demonstrated good performance with an area under the ROC curve of 0.77. CONCLUSIONS: Using a widely available database that requires no additional medical testing or staff training, a useful model for identifying factors associated with 1-year mortality in established long-term care residents can be developed. Widespread use of such a practical approach to assess mortality risk could be of benefit to patients, their families, and physicians for informing care plan decisions.
The Model for End-Stage Liver Disease (MELD) score is now used for allocation in liver transplantation (LT) waiting lists, replacing the Child-Turcotte-Pugh (CTP) score. However, there is debate as whether it is superior to CTP score to predict mortality in patients with cirrhosis on the LT waiting list and after LT. We reviewed studies comparing the accuracy of MELD vs. CTP score in transplantation settings. We found that in studies of the LT waiting list (12,532 patients with cirrhosis), only 4 of 11 showed MELD to be superior to CTP in predicting short-term (3-month) mortality. In addition, 2 of 3 studies (n = 1,679) evaluating the changes in MELD score (DeltaMELD) showed that DeltaMELD had better prediction for mortality than the baseline MELD score. The impact of MELD on post-LT mortality was assessed in 15 studies (20,456 patients); only 6 (9,522 patients) evaluated the discriminative ability of MELD score using the concordance (c) statistic (the MELD score had always a c-statistic < 0.70). In 11 studies (19,311 patients), high MELD score indicated poor post-LT mortality for cutoff values of 24-40 points. In re-LT patients, 2 of 4 studies evaluated the discriminative ability of MELD score on post-LT mortality. Finally, several studies have shown that the predictive ability of MELD score increases by adding clinical variables (hepatic encephalopathy, ascites) or laboratory (sodium) parameters. On the basis of the current literature, MELD score does not perform better than the CTP score for patients with cirrhosis on the waiting list and cannot predict post-LT mortality.
Personal PM(2.5) data from two recent exposure studies, the Scripted Activity Study and the Older Adults Study, were used to develop models predicting 24-h personal PM(2.5) exposures. Both studies were conducted concurrently in the summer of 1998 and the winter of 1999 in Baltimore, MD. In the Scripted Activity Study, 1-h personal PM(2.5) exposures were measured. Data were used to identify significant factors affecting personal exposures and to develop 1-h personal exposure models for five different micro-environments. By incorporating the time-activity diary data, these models were then combined to develop a time-weighted microenvironmental personal model (model M1AD) to predict the 24-h PM(2.5) exposures measured for individuals in the Older Adults Study. Twenty-four-hour time-weighted models were also developed using 1-h ambient PM(2.5) levels and time-activity data (model A1AD) or using 24-h ambient PM(2.5) levels and time-activity data (model A24AD). The performance of these three models was compared to that using 24-h ambient concentrations alone (model A24). Results showed that factors affecting 1-h personal PM(2.5) exposures included air conditioning status and the presence of environmental tobacco smoke (ETS) for indoor micro-environments, consistent with previous studies. ETS was identified as a significant contributor to measured 24-h personal PM(2.5) exposures. Staying in an ETS-exposed microenvironment for 1 h elevated 24-h personal PM(2.5) exposures by approximately 4 microg/m 3 on average. Cooking and washing activities were identified in the winter as significant contributors to 24-h personal exposures as well, increasing 24-h personal PM(2.5) exposures by about 4 and 5 microg/m 3 per hour of activity, respectively. The ability of 3 microenvironmental personal exposure models to estimate 24-h personal PM(2.5) exposures was generally comparable to and consistently greater than that of model A24. Results indicated that using time-activity data with 1-h exposure information, either as micro-environment-specific exposures (model M1AD) or as ambient concentrations (model A1AD), improves our ability to estimate 24-h personal PM(2.5) exposure over the model using 24-h averaged ambient levels alone (model A24). Model performance was higher in the summer than in the winter season. In addition, higher crude R(2) values were reported for subjects participating in both seasons, where the R(2) values equaled.53,.55,.46, and.38 for models M1AD, A1AD, A24AD, and A24, respectively. The low predictive ability of the microenvironmental exposure models in the winter might, in part, be attributed to the narrow dynamic range of personal PM(2.5) exposures.
An animal model was used to test the hypothesis that in heart failure the decrease in the ability to resynthesize ATP through the creatine kinase (CK) reaction (which we call energy reserve) contributes to the inability of the heart to maintain its normal function and contractile reserve. One-week-old turkey poults were fed furazolidone for 14 days to induce dilated cardiomyopathy. Isolated Langendorff-perfused hearts from these myopathic animals showed a 73% decrease in baseline isovolumic contractile performance. Neither increasing [Ca2+]o nor electrical pacing rate increased isovolumic contractile performance. Measured by 31P nuclear magnetic resonance magnetization transfer and chemical assay, ATP concentration was decreased by 23%, phosphocreatine concentration by 42%, CK enzyme activity by 34%, and the pseudo first-order rate constant for the CK reaction by 50%. Measured CK reaction velocity decreased by 71%. The reduced ability to increase cardiac performance in response to increasing [Ca2+]o in hearts with lower CK reaction velocity was reproduced in part by feeding a separate group of turkey poults beta-guanidino-propionic acid to specifically reduce CK reaction velocity by decreasing guanidino substrate concentration. These hearts had normal baseline performance but blunted contractile reserve. These observations provide further support for the hypothesis that a decrease in energy reserve via the CK system contributes to reduced cardiac function in the failing heart.
The three-parameter Sokoloff equation is used to measure the rates of glucose consumption in the brain in vivo. This equation depends linearly on one of its parameters, k1, which is responsible for the glucose transport from plasma to tissue. By equating to zero the first derivative of the minimization function with respect to k1, it is possible to express this parameter as a function of the other two and reduce the non-linear search from three to two dimensions. This approach was examined by the Nelder-Mead simplex method and the Levenberg-Marquardt algorithm. In both cases the process of convergence was more robust and required fewer iterations to achieve a given accuracy than the direct three-parameter non-linear search.
BACKGROUND: Previous studies have reported conflicting results concerning the influence of age and gender on the pharmacokinetics and pharmacodynamics of fentanyl, alfentanil, and sufentanil. The aim of this study was to determine the influence of age and gender on the pharmacokinetics and pharmacodynamics of the new short-acting opioid remifentanil. METHODS: Sixty-five healthy adults (38 men and 27 women) ages 20 to 85 y received remifentanil by constant-rate infusion of 1 to 8 micrograms.kg-1.min-1 for 4 to 20 min. Frequent arterial blood samples were drawn and assayed for remifentanil concentration. The electroencephalogram was used as a measure of drug effect. Population pharmacokinetic and pharmacodynamic modeling was performed using the software package NONMEM. The influence of volunteer covariates were analyzed using a generalized additive model. The performances of the simple (without covariates) and complex (with covariates) models were evaluated prospectively in an additional 15 healthy participants ages 41 to 84 y. RESULTS: The parameters for the simple three-compartment pharmacokinetic model were V1 = 4.98 l, V2 = 9.01 l, V3 = 6.54 l, Cl1 = 2.46 l/min, Cl2 = 1.69 l/min, and Cl3 = 0.065 l/min. Age and lean body mass were significant covariates. From the ages of 20 to 85 y, V1 and Cl1 decreased by approximately 25% and 33%, respectively. The parameters for the simple sigmoid Emax pharmacodynamic model were Ke0 = 0.516 min-1, E0 = 20 Hz, Emax = 5.62 Hz, EC50 = 11.2 ng/ml, and gamma = 2.51. Age was a significant covariate of EC50 and Ke0, with both decreasing by approximately 50% for the age range studied. The complex pharmacokinetic-pharmacodynamic model performed better than did the simple model when applied prospectively. CONCLUSIONS: This study identified (1) an effect of age on the pharmacokinetics and pharmacodynamics of remifentanil; (2) an effect of lean body mass on the pharmacokinetic parameters; and (3) no influence of gender on any pharmacokinetic or pharmacodynamic parameter.