Complexities of sibling analysis when exposures and outcomes change with time and birth order

• Published in: Journal of exposure science & environmental epidemiology Vol. 24; no. 5; pp. 482 - 488
• Main Authors: Sudan, Madhuri, Kheifets, Leeka I, Arah, Onyebuchi A, Divan, Hozefa A, Olsen, Jørn
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01-09-2014; Nature Publishing Group
• Subjects: 692/700/478/174; Behavior; Birth Order; Cell Phone; Cell phones; Cellular telephones; Children; Confidence intervals; Denmark; Environmental Exposure; Epidemiology; Exposure; Female; Humans; Medicine; Medicine & Public Health; original-article; Pregnancy; Prenatal experience; Psychological research; Siblings; cellular phone; confounding; behavior; sibling analysis; child
• ISSN: 1559-0631; 1559-064X
• DOI: 10.1038/jes.2013.56

In this study, we demonstrate the complexities of performing a sibling analysis with a re-examination of associations between cell phone exposures and behavioral problems observed previously in the Danish National Birth Cohort. Children (52,680; including 5441 siblings) followed up to age 7 were included. We examined differences in exposures and behavioral problems between siblings and non-siblings and by birth order and birth year. We estimated associations between cell phone exposures and behavioral problems while accounting for the random family effect among siblings. The association of behavioral problems with both prenatal and postnatal exposure differed between siblings (odds ratio (OR): 1.07; 95% confidence interval (CI): 0.69–1.66) and non-siblings (OR: 1.54; 95% CI: 1.36–1.74) and within siblings by birth order; the association was strongest for first-born siblings (OR: 1.72; 95% CI: 0.86–3.42) and negative for later-born siblings (OR: 0.63; 95% CI: 0.31–1.25), which may be because of increases in cell phone use with later birth year. Sibling analysis can be a powerful tool for (partially) accounting for confounding by invariant unmeasured within-family factors, but it cannot account for uncontrolled confounding by varying family-level factors, such as those that vary with time and birth order.