American journal of epidemiology
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First-generation air bags entail a decreased risk of death for most front seat occupants in car crashes but an increased risk for children. Second-generation air bags were developed to reduce the risks for children, despite the possibility of decreasing protection for others. Using a matched cohort design, the authors estimated risk ratios for death for use of each generation of air bag versus no air bag, adjusted for seat position, restraint use, sex, age, and all vehicle and crash characteristics, among 128,208 automobile occupants involved in fatal crashes on US roadways during 1990-2002. ⋯ Among front seat occupants, the aRR for death with a first-generation air bag was 0.90 (95% confidence interval (CI): 0.86, 0.94); the aRR with a second-generation air bag was 0.89 (95% CI: 0.79, 1.00) (p = 0.83 for comparison of aRRs). Among children under age 6 years, the aRR with a first-generation air bag was 1.66 (95% CI: 1.20, 2.30), while the aRR with a second-generation air bag was 1.10 (95% CI: 0.63, 1.93) (p = 0.20 for comparison of aRRs). The differences in aRRs between first- and second-generation air bags among other subgroups were small and not statistically significant.
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In 2000, body composition, x-ray-defined knee osteoarthritis, and self-reported knee pain information from a cross-sectional, community-based study of 211 African-American and 669 Caucasian women in southeast Michigan (mean age, 47 years) was related to performance-based physical functioning measures to characterize development of functional limitations. Body composition was assessed with bioelectrical impedance. Functioning measures were gait assessment, timed walk, timed stair climb with and without videography, and isometric quadriceps strength. ⋯ Stair climbing correlates included skeletal muscle mass (in kilograms) and its change, painful knee osteoarthritis, and reduced quadriceps strength. Race differences in walking measures and stair climbing time diminished when the authors accounted for other factors. Compromised physical functioning began earlier than expected, with indications that approximately 12-31% of women might benefit from interventions to forestall future decline.
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Circumstances in which both randomized controlled trial and observational study data are available provide an important opportunity to identify biases and improve study design and analysis procedures. In addition, joint analyses of data from the two sources can extend clinical trial findings. The US Women's Health Initiative includes randomized controlled trials of use of estrogen by posthysterectomy women and of estrogen plus progestin by women with a uterus, along with corresponding observational study components. ⋯ These findings support certain combined analyses of the observational data on estrogen and the estrogen plus progestin clinical trial and observational study data to give adjusted observational study estimates of estrogen treatment effects. The resulting treatment effect estimates are compared with corresponding clinical trial estimates, and parallel analyses are also presented for estrogen plus progestin. An application to postmenopausal hormone treatment effects on coronary heart disease among younger women is also provided.
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A case-crossover study was conducted in 36 US cities to evaluate the effect of ozone and particulate matter with an aerodynamic diameter of < or =10 microm (PM10) on respiratory hospital admissions and to identify which city characteristics may explain the heterogeneity in risk estimates. Respiratory hospital admissions and air pollution data were obtained for 1986-1999. In a meta-analysis based on the city-specific regression models, several city characteristics were evaluated as effect modifiers. ⋯ Similarly, a 10-microg/m(3) increase in PM10 during the warm season resulted in a 1.47% (95% CI: 0.93, 2.01) increase in chronic obstructive pulmonary disease at lag 1 and a 0.84% (95% CI: 0.50, 1.19) increase in pneumonia at lag 0. Percentage of households with central air conditioning reduced the effect of air pollution, and variability of summer apparent temperature reduced the effect of ozone on chronic obstructive pulmonary disease. The study confirmed, in a large sample of cities, that exposure to ozone and PM10 is associated with respiratory hospital admissions and provided evidence that the effect of air pollution is modified by certain city characteristics.