Evaluation of an upper extremity student-role functioning scale using item response theory

Millions of workers suffer from upper extremity (musculoskeletal) disorders. Many of these workers are predisposed to upper extremity musculoskeletal disorders because of early exposure to ergonomic risks as students. Computer usage for four or more hours remains the greatest risk for upper extremity musculoskeletal disorders for workers and students alike. Developing preventative methods to reduce student exposure, and thus protect future workers from upper extremity musculoskeletal disorders later in life, requires an appropriate measure for upper extremity musculoskeletal disorder prevalence and related limitations for student functioning. Item response theory analysis was used to evaluate and further develop a upper extremity functioning scale for the student role.     

Introduction: moving youth participation forward

Given the emerging interest among researchers, practitioners, and policymakers in youth participation, it is important to examine and assess carefully the promise and challenges of youth engagement.     

Error catastrophe in mutant mitochondria

The error catastrophe theory of aging, proposed by Orgel in 1963, predicted a decrease in the fidelity of information transfer that accelerated as aging progressed, until properly functioning macromolecules could no longer be reliably made. The theory was extensively tested by comparing DNA polymerases, transfer RNAs, and proteins derived from aging versus young animals, but it did not prove to have general applicability to the process of aging. Recently, the heritable eye disorder progressive external ophthalmoplegia has been found to result from mutation of the gene encoding DNA polymerase gamma, which replicates mitochondrial DNA. The mutant form of the polymerase replicates DNA less accurately than the wild-type enzyme, providing an explanation for the accumulation of mutations in the mitochondrial DNA of patients with this disorder. The affected mitochondria appear to exhibit an age-dependent error catastrophe. It is possible that other genetic diseases might result in error catastrophes in mitochondria as well.     

Choice of Parametric Accelerated Life and Proportional Hazards Models for Survival Data: Asymptotic Results

We discuss the impact of misspecifying fully parametric proportional hazards and accelerated life models. For the uncensored case, misspecified accelerated life models give asymptotically unbiased estimates of covariate effect, but the shape and scale parameters depend on the misspecification. The covariate, shape and scale parameters differ in the censored case. Parametric proportional hazards models do not have a sound justification for general use: estimates from misspecified models can be very biased, and misleading results for the shape of the hazard function can arise. Misspecified survival functions are more biased at the extremes than the centre. Asymptotic and first order results are compared. If a model is misspecified, the size of Wald tests will be underestimated. Use of the sandwich estimator of standard error gives tests of the correct size, but misspecification leads to a loss of power. Accelerated life models are more robust to misspecification because of their log-linear form. In preliminary data analysis, practitioners should investigate proportional hazards and accelerated life models; software is readily available for several such models.     

Measurement error, skewness, and risk analysis: coping with the long tail of the distribution.

Probabilistic risk analyses often construct multistage chance trees to estimate the joint probability of compound events. If random measurement error is associated with some or all of the estimates, we show that resulting estimates of joint probability may be highly skewed. Joint probability estimates based on the analysis of multistage chance trees are more likely than not to be below the true probability of adverse events, but will sometimes substantially overestimate them. In contexts such as insurance markets for environmental risks, skewed distributions of risk estimates amplify the "winner's curse" so that the estimated risk premium for low-probability events is likely to be lower than the normative value. Skewness may result even in unbiased estimators of expected value from simple lotteries, if measurement error is associated with both the probability and pay-off terms. Further, skewness may occur even if the error associated with these two estimates is symmetrically distributed. Under certain circumstances, skewed estimates of expected value may result in risk-neutral decisionmakers exhibiting a tendency to choose a certainty equivalent over a lottery of equal expected value, or vice versa. We show that when distributions of estimates of expected value are, positively skewed, under certain circumstances it will be optimal to choose lotteries with nominal values lower than the value of apparently superior certainty equivalents. Extending the previous work of Goodman (1960), we provide an exact formula for the skewness of products.     

Leading beyond the bottom line, Part 4. The questions it has raised

The Leading Beyond the Bottom Line article series has received an overwhelming response from ACPE members, mostly in enthusiastic support of this new leadership concept. Some of the important questions raised by members are presented with answers from the authors. This article also explores the moral challenge of leadership and why health care is more than a business. In recent years, there's been confusion about the role of the health care enterprise, its leadership and its management. We have lost our way about the "moral" thing, the "right" thing, because we have no philosophy to guide us. To manage or lead in this "business" of health care, a philosophy is required that recognizes the multiple elements to which the leader has responsibility and obligations: the customers, community, employees, and, certainly, the financial assets.     

Customized clinical case management for chronically ill patients. Health system sees remarkable results with teams of case managers,physicians, patients

Securing excellent care and positive outcomes for seriously ill, high-risk patients requires extraordinary measures. A health system in Georgia is experiencing strong results by taking a team approach to health care with case managers, physicians and patients working together.     

Practical Methods for Meeting Remediation Goals at Hazardous Waste Sites

Risk-based cleanup goals or preliminary remediation goals (PRGs) are established at hazardous waste sites when contaminant concentrations in air, soil, surface water, or groundwater exceed specified acceptable risk levels. When derived in accordance with the Environmental Protection Agency's risk assessment guidance, the PRG is intended to represent the average contaminant concentration within an exposure unit area that is left on the site following remediation. The PRG, however, frequently has been used inconsistently at Superfund sites with a number of remediation decisions using the PRG as a not-to-exceed concentration (NTEC). Such misapplications could result in overly conservative and unnecessarily costly remedial actions. The PRG should be applied in remedial actions in the same manner in which it was generated. Statistical methods, such as Bower's Confidence Response Goal, and mathematical methods such as "iterative removal of hot spots," are available to assist in the development of NTECs that ensure the average postremediation contaminant concentration is at or below the PRG. These NTECs can provide the risk manager with a more practical cleanup goal. In addition, an acute PRG can be developed to ensure that contaminant concentrations left on-site following remediation are not so high as to pose an acute or short-term health risk if excessive exposure to small areas of the site should occur. A case study demonstrates cost savings of five to ten times associated with the more scientifically sound use of the PRG as a postremediation site average, and development of a separate NTEC and acute PRG based on the methods referenced in this article.     

Index of Authors Volume 55, 2001

Authors Index

Index of Authors Volume 55, 2001