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PubMed1998

Median and ulnar nerve conduction studies among workers: normative values.

To determine normative values for nerve conduction studies among workers, we selected a subset of 326 workers from 955 subjects who participated in medical surveys in the workplace. The reference cohort was composed exclusively of active workers, in contrast to the typical convenience samples. Nerve conduction measures included bilateral median and ulnar sensory amplitude and latency (onset and peak). Workers with upper extremity symptoms, medical conditions that could adversely affect peripheral nerve function, low hand temperature, or highly repetitive jobs were excluded from the "normal" cohort. Linear regression models explained between 21% and 51% of the variance in nerve function, with covariates of age, sex, hand temperature, and anthropometric factors. The most robust models were fitted for sensory amplitudes in the median and ulnar nerves for dominant and nondominant hands. The median-ulnar difference was least sensitive to adjustment, indicating it is the best measure to use if corrections are not made to account for relevant covariates. A key point was that the magnitude of variance increased with age and anthropometric factors. These findings provide strong evidence that to improve diagnostic accuracy, electrodiagnostic testing should control for relevant covariates, particularly age, sex, hand temperature, and anthropometric factors.

Adult↗

PubMed2002

Risk-adjusted capitation funding models for chronic disease in Australia: alternatives to casemix funding.

Under Australian casemix funding arrangements that use Diagnosis-Related Groups (DRGs) the average price is policy based, not benchmarked. Cost weights are too low for State-wide chronic disease services. Risk-adjusted Capitation Funding Models (RACFM) are feasible alternatives. A RACFM was developed for public patients with cystic fibrosis treated by an Australian Health Maintenance Organization (AHMO). Adverse selection is of limited concern since patients pay solidarity contributions via Medicare levy with no premium contributions to the AHMO. Sponsors paying premium subsidies are the State of Victoria and the Federal Government. Cost per patient is the dependent variable in the multiple regression. Data on DRG 173 (cystic fibrosis) patients were assessed for heteroskedasticity, multicollinearity, structural stability and functional form. Stepwise linear regression excluded non-significant variables. Significant variables were 'emergency' (1276.9), 'outlier' (6377.1), 'complexity' (3043.5), 'procedures' (317.4) and the constant (4492.7) (R(2)=0.21, SE=3598.3, F=14.39, Prob<0.0001. Regression coefficients represent the additional per patient costs summed to the base payment (constant). The model explained 21% of the variance in cost per patient. The payment rate is adjusted by a best practice annual admission rate per patient. The model is a blended RACFM for in-patient, out-patient, Hospital In The Home, Fee-For-Service Federal payments for drugs and medical services; lump sum lung transplant payments and risk sharing through cost (loss) outlier payments. State and Federally funded home and palliative services are 'carved out'. The model, which has national application via Coordinated Care Trials and by Australian States for RACFMs may be instructive for Germany, which plans to use Australian DRGs for casemix funding. The capitation alternative for chronic disease can improve equity, allocative efficiency and distributional justice. The use of Diagnostic Cost Groups (DCGs) is a promising alternative classification system for capitation arrangements.

Journal Article↗

PubMed2005

Patient and physician perspectives of maximum acceptable waiting times for cataract surgery.

BACKGROUND: Lengthy waiting times for cataract surgery are an important issue in countries with publicly funded health care systems. To improve the fairness, timeliness, and certainty of waiting-time management, the Western Canada Waiting List Project has developed priority criteria scores (PCSs) related to urgency and linked to maximum acceptable waiting times (MAWTs). The purpose of our study was to compare patient and physician perspectives of MAWT for different levels of urgency. A second aim was to assess the determinants of patient and surgeon perspectives on MAWT. METHODS: Ophthalmologists assessed consecutive patients waitlisted for cataract surgery. Data included a MAWT, a visual analogue scale of urgency (VAS urgency), and the cataract PCS. Patients were mailed questionnaires to assess their perspectives of MAWT and VAS urgency. They were also sent a measure of visual function called the Visual Function Assessment. We used hierarchical linear regression to assess the determinants of MAWT. RESULTS: The mean age of the 213 patients was 73.9 years; 56.8% were female and 71.8% were booked for first eye surgery. Physician-rated MAWT was significantly longer than patient-rated MAWT (mean 15.1 vs. 9.9 weeks). Median physician MAWTs ranged from 12 (most urgent) to 20 (least urgent) weeks, and patient MAWTs, from 4 to 8 weeks. A 3-step hierarchical linear regression model showed that, after adjusting for age and sex, the priority criteria added significantly to the surgeon model (R2 change = 0.22). Significant predictors were ocular comorbidity, impairment in visual function, and ability to work or live independently or care for dependents. After the addition of VAS urgency, the final model explained 42% of the variance in surgeon MAWT. Significant predictors were age-related macular degeneration and VAS urgency. A 4-step hierarchical regression model for patient MAWT showed that after step 2, sex and visual acuity in the nonsurgery eye were significant predictors. The final model accounted for 11% of the variance in patient MAWT. Significant predictors were sex (males had lower MAWT) and VAS urgency. INTERPRETATION: Patient and physician views on MAWT differ, yet both are critical to a fair process for developing standardized waiting times related to levels of urgency. Results from this study provide initial inputs to the formulation of benchmark waiting times for different levels of the cataract PCS.

Aged↗

PubMed2001

Effect of pH on skin permeation enhancement of acidic drugs by l-menthol-ethanol system.

The effect of pH on the skin permeation enhancement of three acidic drugs by the l-menthol-ethanol system was investigated. The total flux of acidic drugs from the system remarkably varied over the pH range 3.0-8.0, and the permeation enhancement factor depended on the system pH and drug. A skin permeation model, which consists of two permeant (unionized and ionized) species, two system (oily and aqueous) phases, and two permeation (lipid and pore) pathways, was developed. The assumptions were made that only the unionized species can distribute to the oily phase and transport via the lipid pathway. The model explained the relationship between the concentration of drug in the aqueous phase and system pH. The skin permeability data were also described by the model and permeability coefficients corresponding to the physicochemical properties of permeant were calculated for the lipid and pore pathways. The model simulation showed that the permeation of acidic drugs occurred from the aqueous phase and the oily phase acted as a reservoir. Whether the total flux increased with increase of pH was dependent on the lipophilicity of drug. These results suggest that the pH of l-menthol-ethanol system should be given attention to elicit the maximum permeation enhancement.

Animals↗

PubMed2005

Core self-evaluations and job and life satisfaction: the role of self-concordance and goal attainment.

The present study tested a model explaining how the core self-evaluations (i.e., positive self-regard) concept is linked to job and life satisfaction. The self-concordance model, which focuses on motives underlying goal pursuit, was used as an explanatory framework. Data were collected from 2 samples: (a) 183 university students (longitudinal measures of goal attainment and life satisfaction were used) and (b) 251 employees (longitudinal measures of goal attainment and job satisfaction were utilized). In both studies, the core self-evaluations concept was positively related to goal self-concordance, meaning that individuals with positive self-regard were more likely to pursue goals for intrinsic and identified (value-congruent) reasons. Furthermore, in both studies, goal self-concordance was related to satisfaction (job satisfaction in Study 1 and life satisfaction in Study 2).

Adult↗

PubMed2003

Psychopathology and quality of life: psychogenic non-epileptic seizures versus epilepsy.

BACKGROUND: HRQOL is lower in patients with psychogenic non-epileptic seizures (PNES) than in epilepsy patients. Although psychopathology may reduce HRQOL, it is not known whether patients with PNES and epilepsy are similarly affected. We aimed to compare the relationship between psychopathology and HRQOL in PNES and treatment resistant epilepsy. MATERIAL/METHODS: 106 patients with definite diagnosis of PNES or epilepsy were recruited from Epilepsy Monitoring Unit. Patients completed QOLIE-89, Profile of Mood States (POMS), and Adverse Events Profile (AEP). Total Mood Disturbance (TMD) was derived from POMS. We used chi-square and t tests and hierarchical multiple regression to compare HRQOL and its mental status correlates in patients with PNES and epilepsy. RESULTS: Psychiatric history was more prevalent and depression/dejection and TMD were higher in PNES than epilepsy (P<=0.003). PNES patients had a lower adjusted mean HRQOL than epilepsy patients (P<0.01). Mood problems and AEP were strong predictors of HRQOL (P<0.001) and explained the lower HRQOL in PNES vis-l-vis epilepsy. Decreases in HRQOL due to mood problems were similar in both groups. The model explained 62% of the variation in HRQOL. CONCLUSIONS: Although more severe psychopathology in PNES explains the lower HRQOL in PNES relative to epilepsy, the negative association between psychopathology and HRQOL remains stable across the groups. PNES patients with severe mood problems show similar, low levels of HRQOL as patients with severe mood problems who have epilepsy. Future studies should examine causal linkages between psychopathology and PNES and other explanations in seizure-related QOL.

Adult↗

PubMed2006

Surface comparison of active and inactive protein kinases identifies a conserved activation mechanism.

The surface comparison of different serine-threonine and tyrosine kinases reveals a set of 30 residues whose spatial positions are highly conserved. The comparison between active and inactive conformations identified the residues whose positions are the most sensitive to activation. Based on these results, we propose a model of protein kinase activation. This model explains how the presence of a phosphate group in the activation loop determines the position of the catalytically important aspartate in the Asp-Phe-Gly motif. According to the model, the most important feature of the activation is a "spine" formation that is dynamically assembled in all active kinases. The spine is comprised of four hydrophobic residues that we detected in a set of 23 eukaryotic and prokaryotic kinases. It spans the molecule and plays a coordinating role in activated kinases. The spine is disordered in the inactive kinases and can explain how stabilization of the whole molecule is achieved upon phosphorylation.

Algorithms↗

PubMed1996

Screening for osteopenia and osteoporosis: selection by body composition.

There is a great need for simple means of identifying persons at low risk of developing osteoporosis, in order to exclude them from screening with bone mineral measurements, since this procedure is too expensive and time-consuming for general use in the unselected population. We have determined the relationships between body measure (weight, height, body mass index, lean tissue mass, fat mass, waist-to-hip ratio) and bone mineral density (BMD) in 175 women of ages 28-74 years in a cross-sectional study in a county in central Sweden. Dual-energy X-ray absorptiometry was performed at three sites: total body, L2-4 region of lumbar spine, and neck region of the proximal femur. Using multiple linear regression models, the relationship between the dependent variable, BMD, and each of the body measures was determined, with adjustment for confounding factors. Weight alone, in a multivariate model, explained 28%, 21% and 15% of the variance in BMD of total body, at the lumbar spine and at the femoral neck according to these models. The WHO definition of osteopenia was used to dichotomize BMD, which made it possible, in multivariate logistic regression models, to estimate the risk of osteopenia with different body measures categorized into tertiles. Weight of over 71 kg was associated with a very low risk of being osteopenic compared with women weighing less than 64 kg, with odds ratios (OR) of 0.01 (95% confidence interval (CI) 0.00-0.09), 0.06 (CI 0.02-0.22) and 0.13 (CI 0.04-0.42) for osteopenia of total body, lumbar spine and femoral neck, respectively. Furthermore a sensitivity/specificity analysis revealed that, in this population, a woman weighing over 70 kg is not likely to have osteoporosis. Test specifics of a weight under 70 kg for osteoporosis (BMD less than 2.5 SD compared with normal young women) of femoral neck among the postmenopausal women showed a sensitivity of 0.94, a specificity of 0.36, positive predictive value (PPV) of 0.21, and negative predictive value (NPV) of 0.97. Thus, exclusion of the 33% of women with the highest weight meant only that 3% of osteoporotic cases were missed. The corresponding figures for lumbar spine were sensitivity 0.89, specificity 0.38, PPV 0.33, and NPV 0.91. All women who were defined as being osteoporotic of total body weighed under 62 kg. When the intention was to identify those with osteopenia of total body among the postmenopausal women we attained a sensitivity of 0.92 and a NPV of 0.91 for a weight under 70 kg, whereas we found that weight could not be used as an exclusion criterion for osteopenia of femoral neck and lumbar spine. Our data thus indicate that weight could be used to exclude women from a screening program for postmenopausal osteoporosis.

Absorptiometry, Photon↗

PubMed1995

Discrimination of compound gratings: spatial-frequency channels or local features?

Models based on spatial-frequency channels and local features provide alternative explanations for suprathreshold pattern discrimination. We compared psychophysical discrimination data with the predictions of the Wilson and Gelb channel model and three local-feature models. The features were peak-valley local contrast, peak-peak local contrast, and luminance gradients. We measured visual sensitivity for discriminating compound gratings (F + 3F or F + 5F, in peaks-add or peaks-subtract phases) whose component contrasts were yoked together so that a contrast increment in one component was accompanied by an equal decrement in the other. The Wilson and Gelb model accounted for the results with peaks-add gratings, but failed to predict those with peaks-subtract gratings. None of the local-feature models explained the results by themselves. Most of the data fell close to an envelope composed of the lowest thresholds of the three feature-detector models, although there were important exceptions. Our findings are consistent with the view that suprathreshold pattern discrimination is mediated by mechanisms responsive to spatially localized features and that more than one type of feature is used.

Computer Simulation↗

PubMed1990

Awareness of an AIDS campaign directed at Norwegian adolescents.

Awareness of a condom campaign directed at Norwegian adolescents was studied in terms of individual characteristics and social processes. The material comprised a representative sample of 3000 Norwegians aged 17 through 19 years. The response rate was 60.9%. Data were collected by self-administered, anonymous, questionnaires. The campaign consisted of five different elements. The awareness of the elements varied between 50% and 9%. Forty-eight percent reported awareness of at least one element. Six background variables included in a multiple regression model explained only 6% of the variance in awareness of the campaign. In order to illustrate social processes leading to awareness of the campaign, a path model was constructed. Coitus experience, educational aspirations and sex seemed to influence awareness of the campaign through three different paths, in which IPC was included in each path as a intervening variable. Thus, through indirect processes, IPC was mediating the main effects of the three independent variables on awareness. IPC served as a mediating variable between personal characteristics and awareness of the campaign. The results from this study indicate that increasing the adolescents' ability to communicate about sexual topics, are important educational tasks for future prevention of HIV/AIDS.

Acquired Immunodeficiency Syndrome↗

PubMed2006

The constant variation: DNA methylation changes during preimplantation development.

Studies on the DNA methylation changes in the mouse preimplantation embryo suggested a simple and attractive model explaining the process believed to be general in mammals. However, recent reports revealed marked differences between different species that abrogates the universal validity of the model. In order to find an explanation to the differences, we have analyzed the published mouse data and compared them to the observations available in other species. The emerging common theme is the high variability of the methylation at all scales of observation and all levels of organization. This variability is the likely consequence of a dynamic and active redistribution process of the cytosine methylation in the genome.

Animals↗

PubMed2005

Biosocial pathways to functional outcome in schizophrenia.

UNLABELLED: Biosocial models are preeminent in the study of schizophrenia, yet there has been little empirical testing of these models. OBJECTIVE: This study provided the first test of a biosocial causal model of functional outcome in schizophrenia, using neurocognition, social cognition, social competence and social support as predictors of both global and specific domains of functional outcome. METHOD: The design used baseline variables to predict both concurrent functional status and prospective 12-month functional outcome. Subjects were recruited upon admission to outpatient community-based psychosocial rehabilitation programs shown in previous studies to be effective in improving functional outcomes. 139 individuals diagnosed with schizophrenia or schizoaffective disorder participated in the study; 100 participants completed the 12-month assessments. Face-to-face interviews assessed neurocognitive functioning (with five neuropsychological measures), social cognition (as perception of emotion), social competence, social support, and functional outcome which consisted of items covering the domains of social, independent living, and work functioning. RESULTS: Path analysis modeling showed that the proposed biosocial models had strong fit with the data, for both concurrent and 12-month global functional outcomes, with fit indices ranging from .95 to .98. The model explained 21% of the variance in concurrent global functional outcome, and 14% of the variance in 12-month prospective outcome. CONCLUSIONS: The support for this model was strong, and it has implications for understanding the causal factors related to functional outcome, as well as for intervention strategies for improving functional outcomes in schizophrenia.

Adaptation, Psychological↗

PubMed2001

Use of interpolated climatic parameters to predict risk of blowfly-strike in Queensland sheep flocks.

The risk of blowfly-strike was investigated in 160 sheep flocks in Queensland, Australia. The association between blowfly-strike--measured by the use of pesticides in response to flystrike reported by flock managers during the period 1994-1997--and interpolated rainfall and temperature data was examined using survival analysis and stepwise regression. The statistical model explaining the most variation in risk of blowfly-strike included average maximum temperature and its second-order polynomial 4 months preceding flystrike. The model was validated using reports of blowfly-strike from 87 flocks during the period 1997-1999 (collected using the same method as for model construction) and interpolated maximum temperature data. Although there was overlap of 95% confidence intervals derived for model coefficients estimated using both construction and validation data sets, false-negative and false-positive misclassification percentages were 33.3 and 53.3%, respectively. False-negative misclassification was greater for flocks located in southern Queensland, and false-positive misclassification was greater for northern Queensland flocks.

Animals↗

PubMed2005

Coagulation of nanoparticles in reverse micellar systems: a Monte Carlo model.

The process of formation of nanoparticles obtained by mixing two micellized, aqueous solutions has been simulated using the Monte Carlo technique. The model includes the phenomena of finite nucleation, growth via intermicellar exchange, and coagulation of nanoparticles after their formation. Using the model, an exploratory study has been conducted to analyze whether the coagulation of nanoparticles is the reason for the formation of nanoparticles whose sizes are comparable to the size of the reverse micelles. The model explains the possible mechanism of coagulation of semiconductor nanoparticles formed within reverse micelles and its effect on the evolution of their size with time. The model is predictive in nature, and the simulation results compare well with those observed experimentally.

Journal Article↗

PubMed1994

Cumulative effects model: a response to Williams (1994)

The cumulative effects (CE) model explains free-operant choice by the ratio of total numbers of responses and reinforcements, a probability-like variable. Williams (1994) argues that the model is vulnerable to experiments that disprove melioration, a local probability model. The authors note critical differences between the nonlocal CE model and local probability models that allow the CE model to handle some data with which they are incompatible. All models are simplifications of reality; hence, a model's failures are as revealing as its successes. Williams suggests that simple models may need to be abandoned in favor of a "representational" account. The authors point out that representations must be both acquired and acted on. Acquisition requires processing of responses and reinforcers; action requires decision rules. Models are simply testable suggestions for what these rules and processes might be.

Behavior Therapy↗

PubMed1989

Factors affecting outcomes of medication-history interviewing by pharmacy students.

Factors affecting outcomes of medication-history interviewing by pharmacy students were studied. Data were obtained from fourth-year pharmacy students enrolled in a required course in fall 1984. Each student conducted a medication-history interview with one of two simulated patients who presented a predetermined history; interviews were videotaped from behind a one-way mirror. Students also completed an interviewing-orientation survey and a personal report of communication apprehension (PRCA). Trained raters evaluated the videotaped interviews using measures of interview skill and interview completeness. The simulated patients completed a patient-satisfaction form after each interview. Two path models were developed that were identical except that one had completeness and one had patient satisfaction as the dependent variable. Interview skill was the final factor in each model, preceded by variables representing the student's background and orientation factors, PRCA, and simulated-patient gender. Of 112 students conducting the interview, 107 (95.5%) and 95 (84.8%) completed the PRCA and orientation surveys, respectively. The models explained 36% and 27% of the variance in patient satisfaction and completeness, respectively. Shown in parentheses are the significant direct predictors of variables in the model of patient satisfaction: satisfaction (skill, prepharmacy grade point average [preGPA], people and health-care [PHC] orientation); skill (interviewing orientation, preGPA); interviewing orientation PHC orientation, preGPA, PRCA); and (PHC orientation (student gender). All effects were positive except for PRCA on interviewing orientation. For the model of completeness, direct predictors were as follows: completeness (skill, PHC orientation, student gender, simulated-patient gender); skill (interviewing orientation, preGPA); interviewing orientation (PRCA, preGPA, PHC orientation); and PHC orientation (student gender). All effects were positive except for PRCA on interviewing orientation and PHC orientation on completeness. Results suggest that one path model reflects the patient's assessment of interviewer competence in terms of satisfaction, and the other reflects the clinician-rater's assessment of interviewer competence in terms of interview completeness. The interviewing process positively influences both patient satisfaction and interview completeness.

Female↗

PubMed1989

A test of two midfacial growth models using path analysis of normal human fetal material.

Predictions about the temporal sequencing (i.e., primacy) and causal relationships between various midfacial growth components, as suggested by two midfacial growth models (functional matrix and septal traction), were examined in the present study. The relationships between quantitative changes in the nasal septum, nasal airway, nasolabial musculature, and premaxilla of 15 normal human fetal specimens, ranging in age from 12 to 20 weeks postmenstrual age, were assessed using the multivariate technique of path analysis. Path analysis results revealed that the causal sequence of variables proposed by the septal-traction model explained more of the variance in premaxillary size (87 percent goodness-of-fit) than did the sequence of variables proposed by the functional matrix model (65 percent goodness-of-fit). These results suggest that the septal-traction model may be a more parsimonious and primary explanation of early human fetal midfacial growth than the functional matrix model. Path analysis results also reiterate the observed complex developmental relationships within the fetal labioseptopremaxillary region, knowledge of which may be important in the surgical management of infants with complete cleft.

Cross-Sectional Studies↗

PubMed1999

Physical characterization of gravitaxis in Euglena gracilis.

Gravitaxis in unicellular microorganisms like Euglena gracilis has been known for more than 100 years. The current model explains this phenomenon on the basis of a specific density difference between cell body and surrounding medium. In order to test the feasibility of the current model in terms of physical considerations the specific density of different Euglena gracilis cultures was determined. Depending on the culture conditions the specific density was in a range between 1.046 g mL-1 and 1.054 g mL-1. Size and gravitaxis measurements were performed in parallel, which allowed to relate the force applied to the lower membrane to the kinetic properties of gravitactic reorientation. A linear relationship between force and gravitaxis kinetics was found. A comparison between estimated activation energy of the proposed stretch-sensitive ion channels and energy supplied by the displacement of the lower membrane by the sedimentation of the cell body revealed that a focusing, an amplification and/or an integration period over time must be involved in the gravitactic signal transduction chain. Analysis of stimulus-response curves revealed an integration period of about 5 seconds before a gravitactic reorientation starts. The kinetics of gravitaxis at 1 x gn, and 0.12 x gn, was found to be similar. A hypothesis is presented that explains this finding on the basis of a combination of an integration period and an all-or-none reaction during gravitactic reorientation.

Animals↗