Epidemiology
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Exposure to particulate matter (PM) has been associated with deficits in lung function growth among children in Western countries. However, few studies have explored this association in developing countries, where PM levels are often substantially higher. ⋯ Exposure to ambient particulate matter was associated with decreased growth in lung function among Chinese children.
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Weight gain after diagnosis is common among women with breast cancer, yet results have been inconsistent among the few studies examining its effects on survival. ⋯ These results highlight the importance of weight maintenance for women after breast cancer diagnosis.
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Adequate vitamin D status in mothers during pregnancy may influence the health status of the child later in life. We assessed whether maternal circulating 25-hydroxyvitamin D (25[OH]D) concentrations in pregnancy are associated with risk of lower respiratory tract infections, wheezing, and asthma in the offspring. ⋯ Higher maternal circulating 25(OH)D concentrations in pregnancy were independently associated with lower risk of lower respiratory tract infections in offspring in the first year of life but not with wheezing or asthma in childhood.
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Although Berkson's bias is widely recognized in the epidemiologic literature, it remains underappreciated as a model of both selection bias and bias due to missing data. Simple causal diagrams and 2 × 2 tables illustrate how Berkson's bias connects to collider bias and selection bias more generally, and show the strong analogies between Berksonian selection bias and bias due to missing data. In some situations, considerations of whether data are missing at random or missing not at random are less important than the causal structure of the missing data process. Although dealing with missing data always relies on strong assumptions about unobserved variables, the intuitions built with simple examples can provide a better understanding of approaches to missing data in real-world situations.