Epidemiology
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We present results that allow the researcher in certain cases to determine the direction of the bias that arises when control for confounding is inadequate. The results are given within the context of the directed acyclic graph causal framework and are stated in terms of signed edges. Rigorous definitions for signed edges are provided. ⋯ If there is only one unmeasured confounding variable on the graph, then nonincreasing or nondecreasing average causal effects suffice to draw conclusions about the direction of the bias. When there are more than one unmeasured confounding variable, nonincreasing and nondecreasing average causal effects can be used to draw conclusions only if the various unmeasured confounding variables are independent of one another conditional on the measured covariates. When this conditional independence property does not hold, stronger notions of monotonicity are needed to draw conclusions about the direction of the bias.
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Comparative Study
Exposure to cigarette smoke in utero: comparison of reports from mother and daughter.
Smoking during pregnancy has been associated with asthma, obesity, and decreased cognitive functioning in the offspring. To study the role of in utero smoking exposure in offsprings' adult health outcomes, it may be necessary to rely upon reports by the offspring themselves. ⋯ Daughter's report of mother's smoking prenatally and in childhood are good proxy measures for mother's own report of smoking during pregnancy.
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Urban air pollution can trigger asthma symptoms in children, but there is conflicting evidence on effects of long-term exposure on lung function, onset of airway disease and allergic sensitization. ⋯ Exposure to moderate levels of locally emitted air pollution from traffic early in life appears to influence the development of airway disease and sensitization in preschool children.
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The extent to which helmet use reduces the risk of injury in ski- and snowboard-related accidents is unclear. We studied the association of helmet use with injuries of the head, face, and neck among skiers and snowboarders involved in falls and collisions. ⋯ Helmets may provide some protection from head injury among skiers and snowboarders involved in falls or collisions.
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Although the protective effect of oral contraceptives (OCs) use against epithelial ovarian cancer is well-established, there remain gaps in our understanding of the contributions of time-related characteristics of OC use to risk. ⋯ Reduction in epithelial ovarian cancer risk associated with OC use became apparent after a short latency period and short duration of use, and was long-lasting. Time since first use and time since last use seem to modify the association of OCs with ovarian cancer risk independently of duration of use.