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Am J Epidemiol. 2011 May 1;173(9):984-7; reply 988-9. doi: 10.1093/aje/kwq499. Epub 2011 Mar 23.

Invited commentary: causation or "noitasuac"?

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1
Epidemiology Branch, Division of Epidemiology, Statistics, and Prevention Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland 20854, USA. schistee@mail.nih.gov

Abstract

Longitudinal studies are often viewed as the "gold standard" of observational epidemiologic research. Establishing a temporal association is a necessary criterion to identify causal relations. However, when covariates in the causal system vary over time, a temporal association is not straightforward. Appropriate analytical methods may be necessary to avoid confounding and reverse causality. These issues come to light in 2 studies of breastfeeding described in the articles by Al-Sahab et al. (Am J Epidemiol. 2011;173(9):971-977) and Kramer et al. (Am J Epidemiol. 2011;173(9):978-983) in this issue of the Journal. Breastfeeding has multiple time points and is a behavior that is affected by multiple factors, many of which themselves vary over time. This creates a complex causal system that requires careful scrutiny. The methods presented here may be applicable to a wide range of studies that involve time-varying exposures and time-varying confounders.

PMID:
21430191
PMCID:
PMC3121226
DOI:
10.1093/aje/kwq499
[Indexed for MEDLINE]
Free PMC Article
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