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PubMed2000

Modeling traffic-related air pollution in street canyons of Beijing.

It is important to develop a general model to accurately simulate the air pollution in urban street areas. In this paper, the Operational Street Pollution Model (OSPM) initially developed in Denmark is tested with measured data from a relatively wide and open street in Beijing. Major factors influencing the dispersion, such as emission factors, stationary source emissions, and solar radiation, are analyzed. Results show that the model can reflect the basic dispersion pattern in the street but gives systematically higher concentrations. After modifications to estimate street-level wind speed in the model, performance is obviously improved.

Air Movements↗

PubMed2004

[A dynamic knowledge model for nitrogen and water management of cotton].

Through analyzing and extracting the newest research results on nitrogen and water management of cotton, a dynamic knowledge model for decision-making on total nitrogen and water supply levels and their distribution among main growth stages of cotton under different environments and yield targets was developed, with the principles of nitrogen balance and water demand and by integrating the factors of climate, soil, yield and variety. Case studies on the knowledge model with the experiment data sets of different eco-sites, varieties and soil characters indicated a good model performance in decision-making and applicability.

Fertilizers↗

PubMed2004

Environmental variables for modeling wheat yields in the southwest pampa region of Argentina.

Two types of time scales--10-day intervals (D) and phenological phases (P)--were applied to environmental variables for the development of statistical regression models relating to the southwest pampa region of Argentina, with the aim of detecting the effects of weather on wheat yields for the period 1977-1999. The parameters were grouped as meteorological and processed variables and indices. The processed variables used were total soil water availability (SWA) and the ratio of actual evapotranspiration to potential evapotranspiration (alpha), obtained from a water-balance model in which the moisture anomaly index (Z) and the Palmer drought severity index (PDSI) were calculated according to Palmer's model. For these parameters it was possible to establish the times of year and the phenological phases with the best correlation to grain yield. The regression equation for meteorological variables on a 10-day scale provides one of the best fits. Using mixed parameters, the two models, D and P, give rise to a standard error of estimate of approximately 200 kg ha(-1). Truncated models perform better on a P scale than on a D scale. The use of phenological stages improved yield assessment, particularly for those years with extreme meteorological conditions. The optimum models were tested and root-mean-square errors (RMSE) of 440 kg ha(-1) and 470 kg ha(-1) were obtained for P and D scales respectively.

Argentina↗

PubMed1996

Validation of a methodology for modelling PCDD and PCDF intake via the foodchain.

The US EPA foodchain exposure methodology has been assessed, linking background concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in the atmosphere with eventual intake of these chemicals by humans via the foodchain. The methodology is assessed against background environmental concentrations of PCDD/Fs and the background daily adult intake of PCDD/Fs in the UK diet comprising meats, vegetables, dairy produce, fish and miscellaneous food groups. The environmental fate and transport of PCDD/Fs is estimated for each of the seventeen, 2,3,7,8-positional PCDD/F isomers individually from the atmospheric burden in the atmosphere and into the environmental medium or food product of interest. The model predicts PCDD/F deposition rate and soil concentration to within +/-50% of the measured I-TEQ values. For grass, the model underpredicts PCDD/F concentrations but the lack of a reliable and coherent data set precludes further investigation as to the likely causes. The model performs well on food products, with the exception of potatoes (under-predicts by a factor of 20) and 'other' vegetables (underpredicts by a factor of 3). The total modelled PCDD/F intake via the diet is 61 pg I-TEQ day-1 as opposed to the measured intakes of 69 pg I-TEQ day-1 (excluding plant foods) and 81 pg day-1 (including data for plant foods measured in a previous survey, and not representative of contemporary exposures). The major contributor to total PCDD/F intake is via milk and milk products, accounting for about 40% of the daily dietary intake. 'Hidden' fats and oils account for 35% of the PCDD/F intake, followed by the ingestion meat and meat products (12%). As a group, vegetables do not appear to contribute significantly to the total adult background intake of PCDD/Fs via the diet.

Adult↗

PubMed2002

Preoperative risk prediction and intraoperative events in cardiac surgery.

OBJECTIVE: To examine the relationship between preoperative risk prediction and intraoperative events. METHODS: A total of 3118 patients operated in 1999 and 2000 at our institution were analysed, all of whom had their EuroSCORE collected prospectively. The intraoperative variables studied were consultant or trainee operating, long bypass time, long ischaemic time, return on bypass in theatre and use of intra-aortic balloon pump at the end of the procedure. The outcomes are reported as hospital mortality, prolonged length of stay in the intensive therapy unit (pLOS-ITU, >48 h) and death or pLOS-ITU. Risk models were constructed by logistic regression for predicting these three outcomes. RESULTS: With the exception of prolonged cross-clamp time, all variables analysed were independently predictive of a negative outcome. Trainee operating had an apparent protective effect. All risk models performed well. The area under the receiver operating characteristic (ROC) curve (95% CI) increased from 0.857 (0.81, 0.90) for EuroSCORE to 0.874 (0.83, 0.92) for the risk of death model. Similarly, the area under the ROC curve for the pLOS-ITU model increased from 0.687 (0.642, 0.732) to 0.734 (0.691, 0.777) and for the death or pLOS-ITU model from 0.717 (0.677, 0.756) to 0.757 (0.719, 0.795). CONCLUSIONS: Knowledge of adverse intraoperative events enhances preoperative risk prediction. This type of analysis could be used for identifying "near miss" outcomes in adult cardiac surgery.

Cardiac Surgical Procedures↗

PubMed2004

Ergonomics modelling and evaluation of automobile seat comfort.

Automobile seats are developed in an iterative manner because subjective feedback, which is usually of questionable quality, drives the design. The time and cost associated with iteration could be justified if the process was guaranteed to produce a comfortable seat. Unfortunately, this is not the case. Current practices are based on the premise that seat system design teams need objective, measurable laboratory standards, which can be linked to subjective perceptions of comfort. Only in this way can predictions be made regarding whether or not a particular design will be viewed by the consumer as comfortable. This type of forecasting ability would effectively improve the efficiency with which automobile seats are designed. In this context, the research reported, developed, and validated a stepwise, multiple linear regression model relating seat interface pressure characteristics, occupant anthropometry, occupant demographics, and perceptions of seat appearance to an overall, subjective comfort index derived from a survey with proven levels of reliability and validity. The model performance statistics were: adjusted r(2)=0.668, standard error of estimate=2.308, F (6, 38)=15.728, p=0.000, and cross-validated r (15)=0.952, p=0.000. From the model, human criteria for seat interface pressure measures were established. These findings could not have been attained without first demonstrating that (1) the data collection protocol for seat interface pressure measurement was repeatable and (2) seat interface pressure measurements can be used to distinguish between seats.

Analysis of Variance↗

PubMed1997

Testing the self-efficacy-performance linkage of social-cognitive theory.

Past empirical research examining the relationship of self-efficacy perceptions and performance has had several limitations. Most studies were performed in the laboratory with tasks not directly related to individual work performance. As a consequence, many findings are not generalizable to individual work performance. This study tested the self-efficacy-performance model found in Bandura's social-cognitive theory in a work setting, with a sample of 776 American university employees, and with discriminant function analyses. Respondents indicated that performance with computers significantly predicted perceptions of high and low self-efficacy. Results provide additional support for social-cognitive theory as outlined by Bandura.

Adult↗

PubMed1996

Predicting delirium in elderly patients: development and validation of a risk-stratification model.

Delirium is a common and serious complication of acute illness in elderly patients. The aim of this study was to develop and validate a model for predicting development of delirium in elderly medical inpatients who did not have delirium on admission. Consecutive admissions to an acute geriatric unit underwent standardized cognitive assessment every 48 hours. Delirium was diagnosed according to DSM-3 criteria. Independent predictors of delirium in a derivation group of 100 patients were determined using stepwise logistic regression analysis; the predictive model comprised dementia, severe illness and elevated serum urea. This model performed well in a validation group of 84 patients. We conclude that elderly medical patients can be stratified according to their risk for developing delirium using a simple clinical model.

Aged↗

PubMed1992

Analytic sensitivity and specificity of enzyme immunoassay results in testing for human immunodeficiency virus type 1 antibody.

In 1986, a performance evaluation program at the Centers for Disease Control was implemented to assess the quality of performance of laboratories testing for human immunodeficiency virus type 1 antibody and to identify problems that occur during the testing process. Laboratories participating in the Centers for Disease Control Model Performance Evaluation Program for human immunodeficiency virus type 1 antibody testing furnished enzyme immunoassay results after they tested performance evaluation panels that were sent to them in August and November 1989. The panels consisted of 10 individual samples containing antibody-negative and antibody-positive samples, some of which were duplicates. Not all laboratories received the same panel of samples. Low false-negative and false-positive rates, as well as high intrashipment and intershipment reproducibility, indicate that most laboratories did not experience difficulty in testing performance evaluation samples sent to them in August and November 1989.

Evaluation Studies as Topic↗

PubMed2002

The effects of anxiety and strategic planning on visual search behaviour.

The past decade has witnessed increased interest in the visual search behaviour of athletes. Little is known, however, about the relationship between anxiety and eye movements in sport performers or about the extent to which athletes' planned and actual visual search strategies correspond. To address these issues, we conducted two studies. In Study 1, eight expert female gymnasts were presented with three digital slides of a model performing a skill that is known to be anxiety-provoking in this sport--namely, the 'back flip' on the beam. By varying the height of the beam and the presence or absence of safety mats, the slides differed in the amount of anxiety that they elicited vicariously in the viewer. In the study, the gymnasts were asked to imagine themselves in the position of the depicted model and to describe the anxiety that they felt. As they viewed the slides, their eye movements were recorded. As predicted, anxiety was associated with an increase in the number of fixations to peripheral areas. In addition, the more 'threatening' slides elicited significantly more fixations than the less feared images. In Study 2, the plans of 15 equestrian performers (5 expert, 5 intermediate and 5 novice) were elicited as they engaged in a virtual 'walk' around a computerized show-jumping course. Contrary to expectations, the congruence between intended and actual search behaviour was not significantly greater for expert riders than for the less skilled groups. Also, the fact that the top riders allocated more fixations to slides than the less skilled performers challenged the prediction that expertise would be associated with economy of visual search. Finally, as expected, the expert riders were significantly less dependent on the overall 'course plan' than the intermediate and novice equestrian performers when inspecting the fences.

Anxiety↗

PubMed1985

Parametric approaches to the analysis of in vivo cytogenetics studies.

A number of parametric models are evaluated for the analysis of data arising from in vivo cytogenetics studies. Parallels between the structure of data arising from these studies and teratology studies are discussed. Evaluation of historical control data demonstrates the importance of recognizing non-independence of responses among cells within an animal. Models investigated that take into account this non-independence of responses include the beta-binomial, negative binomial, and correlated binomial models. Results indicate that the beta-binomial model performs best in terms of its ability to fit available control data. Suggestions for the incorporation of historical control data, based upon the two-stage structure of the candidate models, are made.

Animals↗

PubMed1992

Two models for transforming auditory signals from head-centered to eye-centered coordinates.

Two models for transforming auditory signals from head-centered to eye-centered coordinates are presented. The vector subtraction model subtracts a rate-coded eye position signal from a topographically weighted auditory target position signal to produce a rate-code of target location with respect to the eye. The rate-code is converted into a place-code through a graded synaptic weighting scheme and inhibition. The dendrite model performs a mapping of head-centered auditory space onto the dendrites of eye-centered units. Individual dendrites serve as logical comparators of target location and eye position. Both models produce a topographic map of auditory space in eye-centered coordinates like that found in the primate superior colliculus. Either type can be converted into a model for transforming visual signals from retinal to head-centered coordinates.

Auditory Perception↗

PubMed2006

A minimal model for the respiratory sinus arrhythmia.

The cardiac and respiratory rhythms in humans are known to be coupled by several mechanisms. In particular, the first rhythm is deeply modulated by the second. In this report we propose a simple operational model for heart rate variability which, taking such modulation into account, reproduces the main features of some experimental sequences of RR intervals recorded from healthy subjects in the resting condition. Also, peer analysis of the model performance allows us to answer the question whether the observed behaviour should be ascribed to phase synchronisation of the heart beating to the respiratory rhythm. Lastly, the changes of the model activity brought about by changing its relevant parameters are analysed and discussed.

Arrhythmia, Sinus↗

PubMed2005

Nonlinear regression and ARIMA models for precipitation chemistry in East Central Florida from 1978 to 1997.

Continuous monitoring of precipitation in East Central Florida has occurred since 1978 at a sampling site located on the University of Central Florida (UCF) campus. Monthly volume-weighted average (VWA) concentration for several major analytes that are present in precipitation samples was calculated from samples collected daily. Monthly VWA concentration and wet deposition of H(+), NH(4)(+), Ca(2+), Mg(2+), NO(3)(-), Cl(-) and SO(4)(2-) were evaluated by a nonlinear regression (NLR) model that considered 10-year data (from 1978 to 1987) and 20-year data (from 1978 to 1997). Little change in the NLR parameter estimates was indicated among the 10-year and 20-year evaluations except for general decreases in the predicted trends from the 10-year to the 20-year fits. Box-Jenkins autoregressive integrated moving average (ARIMA) models with linear trend were considered as an alternative to the NLR models for these data. The NLR and ARIMA model forecasts for 1998 were compared to the actual 1998 data. For monthly VWA concentration values, the two models gave similar results. For the wet deposition values, the ARIMA models performed considerably better.

Acid Rain↗

PubMed2003

Breast cancer risk prediction with a log-incidence model: evaluation of accuracy.

OBJECTIVE: We examined whether a breast cancer risk prediction model other than the Gail et al. model performs better at discriminating between women who will and who will not develop the disease. METHODS: We applied the two published versions of the Rosner and Colditz log-incidence model of breast cancer, developed on data from the Nurses' Health Study, to the estimation of 5-year risk for the period 1992 to 1997 in the same cohort. The first version contained reproductive factors only, and the second version contained a more extensive list of risk factors. RESULTS: Both versions of the model fit well. The ratio of expected to observed numbers of cases (E/O) in the first version was 1.00 (95% confidence interval [CI] 0.93-1.07); for the extended version the E/O was 1.01 (95% CI 0.94-1.09). The age-adjusted concordance statistic was 0.57 for the first model version and 0.63 for the extended version. CONCLUSION: The discriminatory accuracy of the two versions was modest, although the addition of the variables in the extended version meaningfully increased the discriminatory accuracy of risk prediction over that found with the more parsimonious model.

Aged↗

PubMed2005

Predictors of antral follicle count during the reproductive years.

BACKGROUND: We sought to identify indicators of antral follicle count which would be serviceable to clinicians seeking to estimate the number of ovarian follicles without relying on sonographic counts. METHODS: We examined the relations of chronological age and four potential indicators of ovarian age-ovarian volume, FSH, dimeric inhibin B and estradiol-to antral follicle count in 176 recently pregnant women. We identified the regression models which best predict low antral follicle count (< or =10 follicles). RESULTS: Chronological age, ovarian volume, FSH and inhibin B were each significantly associated with antral follicle count. Fifty-three (30.1%) women had < or =10 antral follicles. In the total sample, at the cutpoint corresponding to 80% sensitivity, the positive predictive value for a regression model with all four variables was 60%. All regression models performed less well in women <35 years (13.9% with low count) than in women > or =35 years (52.0% with low count). In older women, the positive predictive value for the model with all four variables was 79%, compared with 60% for a model with chronological age alone. CONCLUSIONS: Our models provide a basis for advising women aged > or =35 years who are either trying to conceive or wish to learn whether they may postpone childbearing.

Adult↗

PubMed2006

Development and validation of a psychiatric case-mix system.

BACKGROUND: Although difficulties in applying risk-adjustment measures to mental health populations are increasingly evident, a model designed specifically for patients with psychiatric disorders has never been developed. OBJECTIVE: Our objective was to develop and validate a case-mix classification system, the "PsyCMS," for predicting concurrent and future mental health (MH) and substance abuse (SA) healthcare costs and utilization. SUBJECTS: Subjects included 914,225 veterans who used Veterans Administration (VA) healthcare services during fiscal year 1999 (FY99) with any MH/SA diagnosis (International Classification of Diseases, 9th Revision, Clinical Modification [ICD-9-CM] codes 290.00-312.99, 316.00-316.99). METHODS: We derived diagnostic categories from ICD-CM codes using Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition definitions, clinical input, and empiric analyses. Weighted least-squares regression models were developed for concurrent (FY99) and prospective (FY00) MH/SA costs and utilization. We compared the predictive ability of the PsyCMS with several case-mix systems, including adjusted clinical groups, diagnostic cost groups, and the chronic illness and disability payment system. Model performance was evaluated using R-squares and mean absolute prediction errors (MAPEs). RESULTS: Patients with MH/SA diagnoses comprised 29.6% of individuals seen in the VA during FY99. The PsyCMS accounted for a distinct proportion of the variance in concurrent and prospective MH/SA costs (R=0.11 and 0.06, respectively), outpatient MH/SA utilization (R=0.25 and 0.07), and inpatient MH/SA utilization (R=0.13 and 0.05). The PsyCMS performed better than other case-mix systems examined with slightly higher R-squares and lower MAPEs. CONCLUSIONS: The PsyCMS has clinically meaningful categories, demonstrates good predictive ability for modeling concurrent and prospective MH/SA costs and utilization, and thus represents a useful method for predicting mental health costs and utilization.

Aged↗

PubMed2002

A cancer survival model that takes sociodemographic variations in "normal" mortality into account: comparison with other models.

STUDY OBJECTIVES: Sociodemographic differentials in cancer survival have occasionally been studied by using a relative survival approach, where all cause mortality among persons with a cancer diagnosis is compared with that among similar persons without such a diagnosis ("normal" mortality). One should ideally take into account that this "normal" mortality not only depends on age, sex, and period, but also various other sociodemographic variables. However, this has very rarely been done. A method that permits such variations to be considered is presented here, as an alternative to an existing technique, and is compared with a relative survival model where these variations are disregarded and two other methods that have often been used. DESIGN, SETTING, AND PARTICIPANTS: The focus is on how education and marital status affect the survival from 12 common cancer types among men and women aged 40-80. Four different types of hazard models are estimated, and differences between effects are compared. The data are from registers and censuses and cover the entire Norwegian population for the years 1960-1991. There are more than 100 000 deaths to cancer patients in this material. MAIN RESULTS AND CONCLUSIONS: A model for registered cancer mortality among cancer patients gives results that for most, but not all, sites are very similar to those from a relative survival approach where educational or marital variations in "normal" mortality are taken into account. A relative survival approach without consideration of these sociodemographic variations in "normal" mortality gives more different results, the most extreme example being the doubling of the marital differentials in survival from prostate cancer. When neither sufficient data on cause of death nor on variations in "normal" mortality are available, one may well choose the simplest method, which is to model all cause mortality among cancer patients. There is little reason to bother with the estimation of a relative-survival model that does not allow sociodemographic variations in "normal" mortality beyond those related to age, sex, and period. Fortunately, both these less data demanding models perform well for the most aggressive cancers.

Adult↗