Complexities of sibling analysis when exposures and outcomes change with time and birth order.
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.
Department of Epidemiology, UCLA School of Public Health, University of California, Los Angeles, California, USA.
Madhuri
M
Sudan
Department of Epidemiology, UCLA School of Public Health, University of California, Los Angeles, California, USA.
Leeka I
LI
Kheifets
1] Department of Epidemiology, UCLA School of Public Health, University of California, Los Angeles, California, USA [2] Department of Public Health, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Onyebuchi A
OA
Arah
HealthCore Inc., Andover, Massachusetts, USA.
Hozefa A
HA
Divan
Institute of Public Health, University of Aarhus, Aarhus, Denmark.
Jørn
J
Olsen
D001722:Birth Order; D040421:Cell Phone; D003718:Denmark; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D011247:Pregnancy; D035781:Siblings