期刊
PAEDIATRIC AND PERINATAL EPIDEMIOLOGY
卷 23, 期 5, 页码 394-402出版社
WILEY-BLACKWELL PUBLISHING, INC
DOI: 10.1111/j.1365-3016.2009.01053.x
关键词
collider-stratification bias; birthweight; directed acyclic graphs; neonatal nortality
资金
- Eunice Kennedy Shriver National Institute of Child Health and Human Development
- National Institutes of Health
- Chercheur-boursier award
- Fonds de la Recherche en Sante du Quebec
- EUNICE KENNEDY SHRIVER NATIONAL INSTITUTE OF CHILD HEALTH & HUMAN DEVELOPMENT [ZIAHD008761] Funding Source: NIH RePORTER
The 'birthweight paradox' describes the phenomenon whereby birthweight-specific mortality curves cross when stratified on other exposures, most notably cigarette smoking. The paradox has been noted widely in the literature and numerous explanations and corrections have been suggested. Recently, causal diagrams have been used to illustrate the possibility for collider-stratification bias in models adjusting for birthweight. When two variables share a common effect, stratification on the variable representing that effect induces a statistical relation between otherwise independent factors. This bias has been proposed to explain the birthweight paradox. Causal diagrams may illustrate sources of bias, but are limited to describing qualitative effects. In this paper, we provide causal diagrams that illustrate the birthweight paradox and use a simulation study to quantify the collider-stratification bias under a range of circumstances. Considered circumstances include exposures with and without direct effects on neonatal mortality, as well as with and without indirect effects acting through birthweight on neonatal mortality. The results of these simulations illustrate that when the birthweight-mortality relation is subject to substantial uncontrolled confounding, the bias on estimates of effect adjusted for birthweight may be sufficient to yield opposite causal conclusions, i.e. a factor that poses increased risk appears protective. Effects on stratum-specific birthweight-mortality curves were considered to illustrate the connection between collider-stratification bias and the crossing of the curves. The simulations demonstrate the conditions necessary to give rise to empirical evidence of the paradox.
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