Nonshared Environmental Influences on Individual Differences in Early Behavioral Development: A Monozygotic Twin Differences Study

Abstract

The monozygotic (MZ) twin differences method was used to investigate nonshared environmental (NSE) influences independent of genetics. Four-year-old MZ twin pairs (N = 2,353) were assessed by their parents on 2 parenting measures (harsh parental discipline and negative parental feelings) and 4 behavioral measures (anxiety, prosocial behavior, hyperactivity, and conduct problems). Within-pair differences in parenting correlated significantly with MZ differences in behavior, with an average effect size of 3%. For the extreme 10% of the parenting-discordant and behavior-discordant distributions, the average NSE effect size was substantially greater (11%), suggesting a stronger NSE relationship for more discordant twins. NSE relationships were also stronger in higher risk environments, that is, families with lower socioeconomic status, greater family chaos, or greater maternal depression.

Differential family and peer environmental factors are related to severity and comorbidity in children with ADHD

“…This finding is comparable with both epidemiological twin (Wichers et al 2001;Asbury et al 2003;Caspi et al 2004;Liang and Eley 2005;Burt et al 2006) and (clinical) sibling studies Murphy et al 2000). We will focus on three main findings.…”

“…Previous studies involving nonshared environmental influences have focused on other psychiatric disorders, e.g., anorexia nervosa (Murphy et al 2000), and other forms of internalizing and externalizing behavior (e.g., Wichers et al, 2001;Asbury et al 2003). Several studies have investigated within-family measures indirectly, e.g., by using difference-scores on variables measured individually for each sibling, while others have used the Sibling Inventory of Differential Experience (SIDE; , a measure that assesses within-family differences directly, by asking siblings about their differential experiences.…”

Differential parent-child relationships and adolescent externalizing symptoms: Cross-lagged analyses within a monozygotic twin differences design.

“…This design capitalizes on the unique features of MZ (identical) twins, specifically that they share both 100% of their genes and their shared environment. As differences between MZ twins, accordingly, cannot be confounded by these factors, this design enables researchers to evaluate more explicitly whether differences in sibling treatment were environmentally linked to child-specific behavior problems.Asbury, Dunn, Pike, and Plomin (2003) used this design in a large sample of 4-year-old MZ twin pairs (n = 2,353) to examine whether sibling differences in parental treatment were linked to child-specific behavior problems. Of importance, however, they also explicitly evaluated whether extreme sibling differences in parental treatment (and extreme differences in sibling behavior problems) potentiated this nonshared environmental relationship.…”

“…First, as noted by Caspi et al (2004), they controlled for continuity in antisocial behavior over time but were not able to control for similar continuity in maternal expressed emotion (as it was not assessed at age 7 years). Accordingly, it remains possible that the association between maternal expressed Second, as noted by Asbury et al (2003) and Caspi et al (2004), studies of nonshared environmental effects typically interpret their findings within a parent-driven framework such that differential parental treatment causes sibling differences in child outcomes. However, these conclusions may be premature.…”

“…Second, as noted by Asbury et al (2003) and Caspi et al (2004), studies of nonshared environmental effects typically interpret their findings within a parent-driven framework such that differential parental treatment causes sibling differences in child outcomes. However, these conclusions may be premature.…”