title: Carryover Effects in Sibling Comparison Designs.
abstract: A convenient way of dealing with confounding is the sibling comparison design, where the outcome in exposed individuals is compared with the outcome in their unexposed siblings. The standard analysis of sibling comparison designs assumes that the exposure and outcome of an individual do not affect the exposure and outcome of his/her siblings, sometimes referred to as an absence of sibling carryover or contagion effects. Unfortunately, there are many situations where carryover effects are likely to be present. In this article, we explore the consequences of carryover effects for sibling comparison designs. We show, using causal diagrams, when and why carryover effects lead to bias, and we investigate the sign and magnitude of this bias under various scenarios.
authors.affiliation: From the aDepartment of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; bClinical Epidemiology Unit, Karolinska Institutet, Stockholm, Sweden; and cDepartment of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA.
authors.forename: Arvid
authors.initials: A
authors.lastname: Sjölander
authors.forename: Thomas
authors.initials: T
authors.lastname: Frisell
authors.forename: Ralf
authors.initials: R
authors.lastname: Kuja-Halkola
authors.forename: Sara
authors.initials: S
authors.lastname: Öberg
authors.forename: Johan
authors.initials: J
authors.lastname: Zetterqvist
mesh_terms: D015982:Bias; D015986:Confounding Factors, Epidemiologic; D003627:Data Interpretation, Statistical; D015340:Epidemiologic Research Design; D006801:Humans; D016013:Likelihood Functions; D016015:Logistic Models; D035781:Siblings