Limitations of therapy

Researchers at the National Institute of Allergy and Infectious Diseases (NIAID) say the immune system's CD4+ T-cells become progressively less diverse as HIV continues to attack the immune system. The information gives more credence to those advocating early treatment of HIV. The cells rebound through antiretroviral drugs but are limited to those types that were present when treatment began. Early treatment is recommended before elements of the immune system are significantly depleted.     

Limitations in the use of job exposure matrices

A Job Exposure Matrix (JEM) is a cross classification of occupations, industries and exposures within a given job. A general JEM covers all occupations and industries. Severe misclassification by using such a JEM is hardly avoidable. Use of a general JEM will therefore rarely be able to identify risk ratios in the moderately elevated range. However, a general JEM could be an important tool in looking for differentiated misclassification, a frequently mentioned problem in case-control studies. Principles of this kind of use is given in the text.     

Limitations of the case-only design for identifying gene-environment interactions

The case-only design, which requires only diseased subjects, allows for estimation of multiplicative interactions between factors known to be independent in the study population. The design is being used as an alternative to the case-control design to study gene-environment interactions. Estimates of gene-environment interactions have been shown to be very efficient relative to estimates obtained with a case-control study under the assumption of independence between the genetic and environmental factors. In this paper, the authors explore the robustness of this procedure to uncertainty about the independence assumption. By using simulations, they demonstrate that inferences about the multiplicative interaction with the case-only design can be highly distorted when there is departure from the independence assumption. They illustrate their results with a recent study of gene-environment interactions and risk of lung cancer incidence in a cohort of miners from the Yunnan Tin Corporation in southern China. Investigators should be aware that the increased efficiency of the case-only design is a consequence of a strong assumption and that this design can perform poorly if the assumption is violated.     

Validity and Reliability of the 8-Item Work Limitations Questionnaire

Purpose To evaluate factorial validity, scale reliability, test–retest reliability, convergent validity, and discriminant validity of the 8-item Work Limitations Questionnaire (WLQ) among employees from a public university system. Methods A secondary analysis using de-identified data from employees who completed an annual Health Assessment between the years 2009–2015 tested research aims. Confirmatory factor analysis (CFA) (n?=?10,165) tested the latent structure of the 8-item WLQ. Scale reliability was determined using a CFA-based approach while test–retest reliability was determined using the intraclass correlation coefficient. Convergent/discriminant validity was tested by evaluating relations between the 8-item WLQ with health/performance variables for convergent validity (health-related work performance, number of chronic conditions, and general health) and demographic variables for discriminant validity (gender and institution type). Results A 1-factor model with three correlated residuals demonstrated excellent model fit (CFI?=?0.99, TLI?=?0.99, RMSEA?=?0.03, and SRMR?=?0.01). The scale reliability was acceptable (0.69, 95% CI 0.68–0.70) and the test–retest reliability was very good (ICC?=?0.78). Low-to-moderate associations were observed between the 8-item WLQ and the health/performance variables while weak associations were observed between the demographic variables. Conclusions The 8-item WLQ demonstrated sufficient reliability and validity among employees from a public university system. Results suggest the 8-item WLQ is a usable alternative for studies when the more comprehensive 25-item WLQ is not available.