Bypassing the selection rule in choosing controls for a case-control study

Objectives It has been argued that in case–control studies, controls should be drawn from the base population that gives rise to the cases. In designing a study of occupational injury and risks arising from long-term illness and prescribed medication, we lacked data on subjects' occupation, without which employed cases (typically in manual occupations) would be compared with controls from the general population, including the unemployed and a higher proportion of white-collar professions. Collecting the missing data on occupation would be costly. We estimated the potential for bias if the selection rule were ignored. Methods: We obtained published estimates of the frequencies of several exposures of interest (diabetes, mental health problems, asthma, coronary heart disease) in the general population, and of the relative risks of these diseases in unemployed versus employed individuals and in manual versus non-manual occupations. From these we computed the degree of over- or underestimation of exposure frequencies and exposure ORs if controls were selected from the general population. Results: The potential bias in the OR was estimated as likely to fall between an underestimation of 14% and an overestimation of 36.7% (95th centiles). In fewer than 6% of simulations did the error exceed 30%, and in none did it reach 50%. Conclusions: For the purposes of this study, in which we were interested only in substantial increases in risk, the potential for selection bias was judged acceptable. The rule that controls should come from the same base population as cases can justifiably be broken, at least in some circumstances. <br/

Assessing Risk Factors for Athletic Excellence

Hardy et al. present a qualitative interview study to identify differences between elite and super-elite athletes, but their approach closely parallels the case-control methodology developed and discussed primarily within the epidemiological literature. The strengths and weaknesses of this approach may be less familiar to a psychological or sports-science audience. Here, I comment on this methodological choice and the implications it has for the robustness and value of the inferences that are drawn. I conclude that while Hardy et al. have made valuable progress in dissecting the factors that generate elite athletic performance, their work is best considered as exploratory, and would benefit greatly from confirmation via a prospective cohort approach

Mortality from infectious pneumonia in metal workers: a comparison with deaths from asthma in occupations exposed to respiratory sensitizers

Introduction: national analyses of mortality in England and Wales have repeatedly shown excess deaths from pneumonia in welders. During 1979-1990 the excess was attributable largely to deaths from lobar pneumonia and pneumonias other than bronchopneumonia, limited to working-aged men, and apparent in other metal fume-exposed occupations. We assessed findings for 1991-2000 and compared the mortality pattern with that from asthma in occupations exposed to known respiratory sensitizers.Methods: the Office of National Statistics supplied data on deaths by underlying cause among men aged 16-74 years in England and Wales during 1991-2000, including age and last held occupation. We abstracted data on pneumonia for occupations with exposure to metal fume and on asthma for occupations commonly reported to surveillance schemes as at risk of occupational asthma. We estimated expected numbers of deaths by applying age-specific proportions of deaths by cause in the population to the total deaths by age in each occupational group. Observed and expected numbers were compared for each cause of death.Results: among working-aged men in metal fume-exposed occupations we found excesses of mortality from pneumococcal and lobar pneumonia (54 deaths vs. 27.3 expected) and from pneumonias other than bronchopneumonia (71 vs. 52.4), but no excess from these causes at older ages, or from bronchopneumonia at any age. The attributable mortality from metal fume (45.3 excess deaths) compared with an estimated 62.6 deaths from occupational asthma.Conclusion: exposure to metal fume is a material cause of occupational mortality. The hazard deserves far more attention than it presently receive

Characterisation and airborne deployment of a new counterflow virtual impactor inlet

A new counterflow virtual impactor (CVI) inlet is introduced with details of its design, laboratory characterisation tests and deployment on an aircraft during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE). The CVI inlet addresses three key issues in previous designs; in particular, the inlet operates with: (i) negligible organic contamination; (ii) a significant sample flow rate to downstream instruments (∼15 l min^(−1)) that reduces the need for dilution; and (iii) a high level of accessibility to the probe interior for cleaning. Wind tunnel experiments characterised the cut size of sampled droplets and the particle size-dependent transmission efficiency in various parts of the probe. For a range of counter-flow rates and air velocities, the measured cut size was between 8.7–13.1 μm. The mean percentage error between cut size measurements and predictions from aerodynamic drag theory is 1.7%. The CVI was deployed on the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter for thirty flights during E-PEACE to study aerosol-cloud-radiation interactions off the central coast of California in July and August 2011. Results are reported to assess the performance of the inlet including comparisons of particle number concentration downstream of the CVI and cloud drop number concentration measured by two independent aircraft probes. Measurements downstream of the CVI are also examined from one representative case flight coordinated with shipboard-emitted smoke that was intercepted in cloud by the Twin Otter

Evaluation of work-related psychosocial factors and regional musculoskeletal pain: results from a EULAR Task Force

Objectives: to establish whether review articles provide consistent conclusions on associations between workplace psychosocial factors and musculoskeletal pain and, if differences exist, to explore whether this is related to the methods used.Methods: reviews, reported up to February 2007, that included consideration of workplace psychosocial factors and upper limb, back or knee pain were identified through searches of multiple databases. The specific work-related psychosocial factors considered were job demands, support, job autonomy and job satisfaction. The conclusions of each review on one or more of the psychosocial/musculoskeletal pain associations were extracted.Results: 15 review articles were identified that considered one or more of the regional pain syndromes included in the study. For back pain, the most consistent conclusions (four reviews positive out of six) were with high job demands and low job satisfaction. The studies of upper limb pain were exclusively related to shoulder and/or neck pain, and the most consistent positive conclusions were with high and low job demands (four reviews positive out of six and two reviews positive out of three, respectively). For knee pain, only a single review was identified. For individual reviews of back and upper limb pain, there were marked differences in the number of associations concluded to be positive between reviews.Conclusions: the reasons for reviews coming to different conclusions included that they were often evaluating different bodies of evidence (according to their search criteria, the year when the review was conducted, the role that quality assessment played in whether studies contributed to evidence, and the combination of risk factors addressed in individual studies), but more important was whether the review specified explicit criteria for making conclusions on strength of evidence. These conclusions emphasise the importance of developing standardised methods for conducting such evaluations of existing evidence and the importance of new longitudinal studies for clarifying the temporal relationship between psychosocial factors and musculoskeletal pain in the workplac

A Lie algebra attached to a projective variety

Each choice of a K\"ahler class on a compact complex manifold defines an action of the Lie algebra \slt on its total complex cohomology. If a nonempty set of such K\"ahler classes is given, then we prove that the corresponding \slt-copies generate a semisimple Lie algebra. We investigate the formal properties of the resulting representation and we work things out explicitly in the case of complex tori, hyperk\"ahler manifolds and flag varieties. We pay special attention to the cases where this leads to a Jordan algebra structure or a graded Frobenius algebra.Comment: AMSTeX v2.1, 46 page