RESUMEN
In this work, we present a theoretical analysis of diffusion processes at arrays of recessed microelectrodes and evaluate the dependence of these processes on the main geometrical parameters (distance between electrodes in the array and slope of side walls of conical recesses) of this complex system. To allow for faster computation time and excellent accuracy, numerical simulations were performed upon transforming the real space allowed for diffusion using a quasi-conformal mapping introduced for this array geometry in our previous work (Amatore, C., Oleinick, A. I. and Svir, I. J. Electroanal. Chem. 2006, 597, 77-85). The applied quasi-conformal mapping is perfectly suited to the considered microelectrode array geometry and ensures that the abrupt change of boundary conditions reflecting the contorted geometries of the considered microelectrode array are treated efficiently and precisely in the simulations.
RESUMEN
STUDY DESIGN: A retrospective cohort study of Michigan workers' compensation cases involving back injuries in 1986 and 1987 with incidence and outcome data. OBJECTIVE: To determine claim rates by age, gender, and industry or occupation for compensable back injuries and to investigate the relation between occupation and return to work. SUMMARY OF BACKGROUND DATA: The cohort of 24,094 Michigan workers' compensation cases from 1986 and 1987 in which claimants were compensated for back injuries was reviewed. Compensation eligibility requires more than 7 days' disability after injury. METHODS: Claim rates for back injuries by age, gender, and industry or occupation using employment data interpolated from 1980 and 1990 Census 1% Public Use Microdata Samples. Cox proportional hazards analysis was performed for return to work in the first 8 weeks after injury, with occupation coded at the three-digit level. RESULTS: All-age claim rates for Michigan compensable back injuries by occupation ranged between 0.03% and 1.7% annually (0.39% for all cases) and were generally higher in women in white collar occupations and in men in blue collar occupations. The claim rate peaked in men in the 25-34 year range, with the highest rates in manual labor occupations. The peak claim rates by age were less marked in women, tending to occur broadly throughout the 25-44-year range. Similar all-age values were recorded by industry. The male-to-female risk ratio over all occupations does not vary by age and is approximately 1.4:1. As the classification of occupation became more detailed, large differences in risk were documented within major occupation groups. The highest risk in this study was approximately 6% annually for 25-44 year old men in driver-sales (beverage truck drivers and delivery workers). Only 7 of 40 occupation categories showed a significant relative hazard for return to work in the first 8 weeks after injury, and these were blue collar occupations with earlier return than the reference sales category. For Michigan compensable back injuries, a rough estimate of the true annual incidence of new claims is 94% of the reported claim rate. CONCLUSIONS: The relative risk of compensable back injury is generally higher for females in white collar occupations, higher for males in blue collar occupations and approximately equal in service occupations. Although the risk of back injury is related to occupation, the same occupational factors do not operate as a barrier to return to work.
Asunto(s)
Traumatismos de la Espalda/epidemiología , Enfermedades Profesionales/epidemiología , Indemnización para Trabajadores/estadística & datos numéricos , Adolescente , Adulto , Distribución por Edad , Traumatismos de la Espalda/psicología , Estudios de Cohortes , Femenino , Humanos , Incidencia , Formulario de Reclamación de Seguro , Masculino , Michigan/epidemiología , Persona de Mediana Edad , Enfermedades Profesionales/psicología , Ocupaciones , Modelos de Riesgos Proporcionales , Estudios Retrospectivos , Factores de Riesgo , Distribución por SexoRESUMEN
STUDY DESIGN: A retrospective cohort of 2425 workers with compensated back conditions was created from the 1991 compensated cohort of the largest compensation insurer in Michigan by linking computerized information on social and demographic factors, diagnostic and management procedures, and cumulative missed worktime. OBJECTIVE: To describe medical care use from date of injury in 1991 to mid-1993 by type of back condition, to identify factors affecting this use, to determine the effect of alternative model selection strategies on identifying such factors, to investigate the timing of surgery and the use of diagnostic studies in patients with displaced or herniated discs with and without surgery, and to compare the use of medical care in the study group with that recommended by national expert panels. SUMMARY OF BACKGROUND DATA: Despite the enormous costs involved in medical care for patients with work-related back injuries, almost no information on the use of medical care is available for compensated back injuries by diagnostic and procedure code. METHODS: Use of medical care was grouped into 18 categories for tabulation. Factors affecting use of medical care were identified by logistic regression, supplemented by Cox analysis for time to first procedure. The Hosmer-Lemeshow chi-square statistic was compared with the Bayes Information Criterion for evaluating model fit. Overall model utility was evaluated by comparing receiver operating characteristic curves generated by the model. For patients with displaced or herniated discs, algorithms were used to identify the diagnostic procedures performed before and after the first surgery and the amount of time that passed before each procedure was performed. RESULTS: In patients with diagnoses of disc displacement or herniation or vertebrogenic neuritis, approximately 80% underwent radiography to obtain plain views of the spine, 75% underwent diagnostic imaging, 45% underwent electrodiagnostic procedures, and 24% underwent spinal surgery (29.3% had surgical procedures among those with disc conditions). In patients with diagnoses of back sprain or other symptomatic diagnoses, the percentages for the first three procedures are approximately 70%, 12%, and 12%, respectively. Diagnostic category, age, gender, and cumulative missed worktime predicted the receipt of diagnostic and treatment procedures. Women were 30% less likely to undergo computed axial tomography or magnetic resonance imaging and 50% less likely to undergo spinal surgery. Median time to spinal surgery was twice as long in the group that underwent diagnostic imaging and electrodiagnostic testing before surgery (134.5 days). Of the 622 patients with disc displacement/herniation, 510 (approximately 80%) had initial diagnostic imaging studies, and, of the 510, 162 (approximately 30%) had surgery. Thirteen (8%) were reoperated. Of the 162 patients who had surgery, 46 (approximately 30%) had follow-up diagnostic imaging, and, of the 46, nine (approximately 20%) were reoperated. Of the 348 managed conservatively, 96 (approximately 30%) had follow-up diagnostic imaging. CONCLUSIONS: The data suggest only modest differences in the use of medical care between this study group and noncompensated study populations from previous reports. The authors of this study estimate that 27% of diagnostic imaging studies and 43% of plain radiography of the spine could have been avoided if then available Canadian recommendations or current American, guidelines had been followed. The gender effect remains unexplained and needs to be investigated in additional studies. There was an increase of 6% in the use of surgery in compensated patients compared with the use of surgery in a recent American series involving traditional health insurance, but this may be associated with greater work disability in the compensated group. The results of the current study suggest that the use and reporting of model selection strategies and the use of receiver operati
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Traumatismos de la Espalda/diagnóstico , Traumatismos de la Espalda/epidemiología , Servicios de Salud/estadística & datos numéricos , Indemnización para Trabajadores/estadística & datos numéricos , Adolescente , Adulto , Distribución por Edad , Traumatismos de la Espalda/cirugía , Estudios de Cohortes , Bases de Datos Factuales , Femenino , Humanos , Modelos Logísticos , Masculino , Michigan/epidemiología , Persona de Mediana Edad , Enfermedades Profesionales/diagnóstico , Enfermedades Profesionales/epidemiología , Valor Predictivo de las Pruebas , Estudios Retrospectivos , Distribución por Sexo , Procedimientos Quirúrgicos Operativos/estadística & datos numéricosRESUMEN
Occupational back injuries produced $27 billion in direct and indirect costs in 1988. Predictors of prolonged disability have generally been identified in selected clinical populations, but there have been few population-based studies using statewide registries from workers' compensation systems. This study uses a 1986 cohort of 8,628 Michigan workers with compensable back injuries followed to March 1, 1990. Cox proportional hazards analyses with nine categorical covariates identified factors predicting missed worktime for the first disability episode following the injury. The model distinguished factors affecting the acute (< or = 8 weeks) and chronic disability periods (> 8 weeks). The first disability episode following injury contains 69.6% of the missed worktime observed through follow-up. In the acute phase, which contributes 15.2% of first episode missed worktime, gender, age, number of dependents, industry (construction), occupation, and type of accident predict continued work disability. Marital status, weekly wage compensation rate, and establishment size do not. Beyond 8 weeks, age, establishment size and, to a lesser degree, wage compensation rate predict duration of work disability. Graphs show the predicted disability course for injured workers with specific covariate patterns. Future efforts to reduce missed worktime may require modifications in current clinical practice by patient age group and the development of new strategies to encourage small and medium-size employers to find ways to return their injured employees to work sooner. Recent federal statutes covering disabled workers will only partially correct the strong effect of employer establishment size.
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Dolor de Espalda/epidemiología , Enfermedades Profesionales/epidemiología , Ausencia por Enfermedad , Traumatismos Vertebrales/epidemiología , Indemnización para Trabajadores , Adolescente , Adulto , Anciano , Dolor de Espalda/economía , Enfermedad Crónica , Femenino , Humanos , Masculino , Michigan/epidemiología , Persona de Mediana Edad , Enfermedades Profesionales/economía , Modelos de Riesgos Proporcionales , Reproducibilidad de los Resultados , Factores de Riesgo , Sensibilidad y Especificidad , Traumatismos Vertebrales/economía , Factores de Tiempo , Indemnización para Trabajadores/economía , Indemnización para Trabajadores/legislación & jurisprudenciaRESUMEN
The current BLS Annual Survey of Occupational Illnesses and Injuries and several recent analyses of factors affecting missed worktime in occupational back injuries rely on ANSI-based injury codes derived from injury narratives to classify occupational injuries and estimate incidence and outcome. No population-based studies of the concordance between back injury codes and clinical diagnoses have been reported. Back injury cases were identified in two large work-injured populations totaling almost 80,000 cases in the states of Michigan and Minnesota. In both populations, cases had been coded by the single nature-of-injury and part-of-body-injured codes assigned by an ANSI-based injury-coding system and by as many as four (Michigan) or three (Minnesota) clinical diagnoses according to the International Classification of Diseases-Clinical Modification, 9th Revision. Concordance was measured by the sensitivity and predictive value positive (PVP, aka PV+ or PPA) of the injury coding scheme for related diagnostic groups. We also used an algorithm based on the limited clinical information available to corroborate the diagnosis of displaced/herniated disc for cases that underwent spinal surgery. Cases identified by the algorithm were then used to obtain a lower bound estimate of the fraction with disc injury. The injury coding scheme had PVPs of 82.9-90.1% and overall sensitivities of 69.7-75.9%. Sensitivities for individual diagnostic groups show that their distribution in ANSI-coded injury groups is skewed slightly toward cases with sprain and disc displacement/herniation, but these shifts are modest. The lower bound estimate of the fraction of cases with disc displacement/herniation in a population of cases with back injuries producing at least 1 day of missed worktime is 5.8%. The demographic comparisons indicate that, as the time between injury and cohort ascertainment increases during the first 8 days of missed worktime following injury, the proportion of younger workers in an injury cohort decreases. The relationship between increasing age and increasing missed worktime disability, reported in various outcome studies, is also present during the first few days following injury. The use of ANSI injury codes underestimates the contribution of back injuries to missed worktime because 24-30% of cases are missed by the ANSI coding system. However, the distribution of diagnostic groups in the injury-coded groups approximates that observed with all diagnosed cases and supports the use of such data to study outcome. Our estimate, and one from Quebec, suggest that disc displacement/herniation occurs more frequently in the subset of occupational back injuries compared to the set of back injuries from all sources.
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Evaluación de la Discapacidad , Desplazamiento del Disco Intervertebral/clasificación , Enfermedades Profesionales/clasificación , Indemnización para Trabajadores , Adolescente , Adulto , Distribución por Edad , Femenino , Humanos , Desplazamiento del Disco Intervertebral/epidemiología , Masculino , Sistemas de Registros Médicos Computarizados , Michigan/epidemiología , Persona de Mediana Edad , Minnesota/epidemiología , Enfermedades Profesionales/epidemiología , Valor Predictivo de las Pruebas , Distribución por Sexo , Ausencia por Enfermedad , Estados UnidosRESUMEN
For many years, the annual survey of occupational injuries and illnesses by the Federal Bureau of Labor Statistics (BLS) has consistently reported, without explanation, that injury rates in the smaller establishments (< 50 employees) are substantially lower than those for midsize establishments (100-499 employees). Also during those years, a remarkable increase has been reported in the injury rate in large companies, following the imposition of stiff fines for failure to keep required injury records. The rate patterns are identical for Michigan and the country in general. We investigated possible causes for lower injury rates in small establishments since such rates are inconsistent with reports of higher fatality rates in small establishments in the mining, construction, manufacturing, and transportation industries and higher, or at least comparable, injury rates for small establishments in the mining industry. They are also inconsistent with increased turnover and decreased availability of occupational safety services in small companies. Moreover, injury severity, as measured by missed worktime, is greater for workers in small establishments. We investigated the possibility that interactions of workforce or injury characteristics with establishment size could explain the rate differences. We also reviewed the available literature to see whether differences in labor turnover rates could explain the BLS findings. Graphical and statistical analyses of the 1988 CPS Annual Demographic File, a sample of employed persons in the U.S. workforce, failed to identify any associations between workforce characteristics and enterprise size that would explain the lower rates. Similarly, graphical and statistical analyses of all Michigan workers incurring a compensable injury in 1986 failed to indicate any associations between injury characteristics and establishment size that would explain the lower rates. The potential role of labor turnover on the injury rate was analyzed from data in the literature on turnover rate by establishment size and risk of injury by time on the job. None of these analyses explains the lower injury rates reported for small establishments. This leaves underreporting of injuries from small establishments as a substantial possibility. If small establishments were subject to the same injury incidence rates as midsize establishments, then the 1986 survey for Michigan may have missed as many as 54,000 injuries (and far more nationally). We suggest that BLS undertake methodological studies to validate the completeness of reporting from small establishments.
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Accidentes de Trabajo/estadística & datos numéricos , Lugar de Trabajo , Heridas y Lesiones/epidemiología , Absentismo , Adolescente , Adulto , Distribución por Edad , Distribución de Chi-Cuadrado , Documentación/normas , Femenino , Encuestas Epidemiológicas , Humanos , Incidencia , Masculino , Michigan/epidemiología , Persona de Mediana Edad , Salud Laboral/estadística & datos numéricos , Ocupaciones , Reproducibilidad de los Resultados , Distribución por Sexo , Estados Unidos/epidemiología , United States Occupational Safety and Health Administration , Indemnización para Trabajadores/estadística & datos numéricosRESUMEN
National and state estimates of the severity of occupational injuries and illnesses (severity = lost work time = missed work days+restricted work days) have come from the annual Survey of Occupational Injuries and Illnesses (Survey) produced by the U.S. Bureau of Labor Statistics. However, we show that the Survey practice of collecting injury information soon after the accident year reduces substantially the accuracy of missed work day estimates, which constitute 85.3% of the Survey lost work time estimate. To develop an independent estimate of missed work days, the research team created the Michigan Comprehensive Compensable Occupational Injury Database (Michigan Database) by linking state files with injury characteristics to files with workers' compensation information for injuries occurring in 1986. The measure of missed work time (days, weeks, or years) is the cumulative duration of compensation from the "date disability commenced," noted on the first payment form, through follow-up to March 1, 1990. Cumulative missed work time has been calculated or estimated for 72,057 injured workers, more than 97% of the 73,609 Michigan workers with compensable occupational injuries in 1986 identified through the close of the study. Our "best" estimate of missed work days, to follow-up, attributable to both fatal and nonfatal compensable occupational injuries and illnesses is 7,518,784, a figure four times that reported for Michigan by the Survey. When insurance industry data on disbursements are also considered, the estimate of missed work days increases to 8,919,079, a figure 4.75 times that reported by the Survey. When insurance data on reserves for future payments are also considered, the estimate of missed work days increases to 16,103,398, a figure 8.58-fold greater than that obtained for Michigan in the Survey. The Michigan data suggest that the national Survey may have failed to identify almost 373 million of 421 million missed work days in the private sector that have resulted, or will result, from 1986 occupational injuries. The present federal/state system for estimating occupational injury severity by measuring lost work days seriously underestimates the magnitude of the problem. The current policy of obtaining incidence and severity data from the same Survey should be reconsidered. We recommend that national estimates of injury severity be obtained from representative states by using state compensation data and that such estimates be used to evaluate current prevention and rehabilitation strategies. The redesigned occupational safety and health Survey (ROSH Survey) should be revised to permit linkage to compensation data.