Peer Network Overlap in Twin,Sibling, and Friend Dyads

Research suggests that sibling–peer connections are important for understanding adolescent problem behaviors. Using a novel behavioral genetic design, the current study investigated peer network overlap in 300 child–child pairs (aged 7–13 years) in 5 dyad types: monozygotic (MZ), dizygotic twins, full siblings (FSs), friend pairs, and virtual twins (i.e., same‐aged, genetically unrelated siblings). Genetic relatedness, sex composition, and age differences contributed to peer overlap in sibling dyads. MZ twins showed the highest overlap (82%), opposite‐sex FS pairs showed the lowest overlap (27%), and friend pairs (48%) were close to the mean (53%). Social contact variables and self‐reported relationship intimacy predicted additional variance in peer overlap. The roles of genotype–environment correlational and shared environmental processes in the sibling–peer connections are discussed.     

Genetic and Environmental Influences on Perceptions of Self-Worth and Competence in Adolescence: A Study of Twins, Full Siblings, and Step-Siblings

Although it is generally assumed that the origins of adolescents' perceptions of self-competence lie in shared family environmental influences, the contributions of nonshared environmental or genetic influences have not been explored. We investigated sibling resemblance for perceived competence and self-worth in 720 adolescent pairs aged 10 to 18 years, using a twin, full sibling, and step-sibling design. Our goals were to assess the magnitude of shared and nonshared environmental influences and to disentangle resemblance due to shared genetic heritage from that due to shared environmental experiences. Shared environment was not significant for any of the scales. 4 of the subscales showed significant genetic influence: scholastic, social, physical, and athletic competence. We also explored possible sources of genetic influences on perceived competence. Bivariate models revealed common genetic variance between scholastic competence and vocabulary and social competence and sociability. These measures, however, did not account for all of the genetic variance in perceived social and scholastic competence.     

A genetically sensitive investigation of the effects of the school environment and socio‐economic status on academic achievement in seven‐year‐olds

Although it is well established that school characteristics (SCH) and socio‐economic status (SES) are associated with academic achievement (ACH), these correlations are not necessarily causal. Because academic achievement shows substantial genetic influence, it is useful to embed such investigations in genetically sensitive designs in order to examine environmental influences more precisely by controlling genetic influence on ACH. In the first study of this kind for academic achievement, data were collected for 1,063 same‐sex pairs of seven‐year‐old MZ and DZ twins for teacher‐assessed ACH, UK statistics on SCH, and parent‐reported SES. Exclusive of genetic influence on school achievement, shared environment (environmental influences that make siblings similar) accounts for 12% of the variance in academic achievement. SCH accounts for 17% and SES accounts for 83% of this shared environmental variance. Exclusive of genetic and shared environmental influence including SCH and SES, nonshared environment (environmental influences that do not make siblings similar) accounts for 19% of the variance in academic achievement. The importance of nonshared environmental influences on academic achievement leads to the question of what these child‐specific experiences might be that are not shared by children in the same family, school, and classroom.     

A Twin Study of Attachment in Preschool Children

The degree to which individual differences in child-parent attachment were mediated by genetic, shared environmental, and nonshared environmental influences was investigated. One hundred and ten preschool-aged twin pairs (N = 220) were assessed in the Strange Situation and coded using conventional four-way classifications and a continuous measure of attachment security. The degree of sibling similarity in attachment was substantial, with an overall concordance rate of 67% at the secure/insecure level. The degree of concordance was equally high in monozygotic and dizygotic twin pairs, 70% and 64%, respectively, suggesting little genetic influence but a moderate degree of discordance. Twin similarity on the continuous measure of attachment security was r(57) = .48 and r(53) = .38 for monozygotic and dizygotic twin pairs, respectively, also consistent with a modest role for genetic influence but a significant effect for shared and nonshared environment. The implications for genetic influences on the environment and for understanding nonshared and shared environmental influences are discussed.     

Adolescent, parent, and observer perceptions of parenting: genetic and environmental influences on shared and distinct perceptions

Agreement among reporters on features of family life, whether family members or outside observers, is considered to be low. This study, which involved a national sample of 720 families comprised of identical and fraternal twins, full siblings, half siblings, and biologically unrelated stepsiblings, examined the issue of low interrater agreement by decomposing the common and unique variance among parent, child, and observer reports of parenting behaviors (warmth and negativity) into genetic and environmental factors. Quantitative genetic analyses were employed to decompose the "Social" level of perception (common variance among parents, children, observers), the level of "Family" subculture (common variance only among parents and children), and the unique "Individual" level into genetic and environmental components. It was predicted that genetic factors would account for substantial portions of the variance at the Social and Family levels; nonshared environmental factors were expected to influence variance unique to child reports; and shared environmental factors were expected to influence variance unique to parent reports. A second and related aim of the study was to examine the subjective-objective dimension of genetic effects on measures of the environment. Results of model-fitting analyses generally supported the predictions for parental warmth and negativity at the Family and Individual levels. At the Social level, genetic factors were predominant for parental negativity and shared environmental factors for parental warmth. The findings are discussed in terms of genetically influenced child effects on parenting and methodological difficulties in constructing latent variables.     

Genetic and environmental influences on sex-typed behavior during the preschool years

The genetic and environmental etiologies of sex-typed behavior were examined during the preschool years in a sample of 3,990 three- to four-year-old twin and non-twin sibling pairs. Results showed moderate genetic and significant shared environmental influence for boys and substantial genetic and moderate shared environmental influence for girls. For both boys and girls, twin-specific shared environmental effects contributed to twins' similarity in gender role behavior and accounted for approximately 22% of the shared environmental variance. These findings extend previous research conducted with older samples by showing not only important genetic contributions to gender role behavior but also an important role for shared environment. The inclusion of non-twin siblings showed that some of the shared environmental influence is specific to twins.     

Individual differences in dynamic measures of verbal learning abilities in young twin pairs and their older siblings

We explored the genetic background of individual differences in dynamic measures of verbal learning ability in children, using a Dutch version of the Auditory Verbal Learning Test (AVLT). Nine-year-old twin pairs (N = 112 pairs) were recruited from the Netherlands Twin Register. When possible, an older sibling between 10 and 14 years old participated as well (N = 99). To assess verbal learning, non-linear curves were fitted for each child individually. Two parameters were estimated: Learning Speed (LS) and Forgetting Speed (FS). Larger twin correlations in monozygotic (MZ) than in dizygotic (DZ) and sibling pairs for LS and FS indicated the importance of genetic factors in explaining variation in these traits. The heritability estimate (percentage of variance explained by genetic factors) for LS was 43% for both twins and siblings. For FS heritability was estimated at 20% in twins and was slightly higher (30%) in their older siblings.     

Behavior problems among children from different family structures: the influence of genetic self-selection

To examine both genetic and environmental influences on children's behavior problems in households defined by marital status and sibling relatedness, this study applied behavioral genetic methodology to four groups totalling 1524 sibling pairs drawn from 796 households: (1) two-parent full siblings, (2) two-parent half siblings, (3) mother-only full siblings, and (4) mother-only half siblings. Model-fitting procedures found that within-group variation on four subscales from the Behavior Problems Index was best explained by a model including both genetic and shared environmental factors. This model was then fit to the behavior problems means of the four groups. Its successful fit to these mean structures suggested that mean-level differences between groups were explained with the same influences that accounted for within-group variation. Genetic influences accounted for 81% to 94% of the mean-level difference in behavior problems between the two-parent, full sibling and the mother-only, half sibling groups. In contrast, shared environmental influences accounted for 67% to 88% of the mean-level difference in behavior problems between the two-parent, full sibling and mother-only, full sibling groups. The genetic influences are interpreted in terms of genetic self-selection into family structures.     

Sibling differentiation in adolescence: implications for behavioral genetic theory

The presence of sibling "differentiating processes"--defined as processes in which increased sibling similarity in environmental or genetic factors leads to differences in sibling outcomes-poses a challenge for standard behavioral genetic theory and research. The presence of differentiation processes may affect estimates of genetic and environmental parameters in ways that have not been fully recognized. Utilizing data from the Nonshared Environment and Adolescent Development project, this study examined whether differentiating processes existed for seven composite indices of positive and negative adolescent adjustment. The 720 sibling pairs in the study were broken down into groups by age difference (0-4 years) between siblings. The hypothesis that siblings close in age would demonstrate lower correlations on adjustment measures was generally supported at two time points, three years apart. However, siblings one year apart at Time 1 were more similar to each other than were siblings two years apart, suggesting that shared environmental influences counteract sibling differentiation processes for these siblings. The overall trend supporting sibling differentiation was found to be unrelated to measures of sibling positivity and negativity.     

Environmental differences within the family and adjustment differences within pairs of adolescent siblings

To what extent do siblings in the same family experience different parental treatment, sibling interaction, and peer relationships? Are such within-family experiential differences related to differences in the siblings' emotional adjustment? The present study explored these questions concerning within-family environment using data from 348 families that each included 2 siblings 11-17 years of age. The results indicate that siblings in the same family experience different environments, as reported by parents and to a larger extent by the siblings themselves. The results also demonstrate that within-family environmental differences are related to differences in development between siblings. Both the parent and sibling reports of the environment converge on the finding that the sibling who is more psychologically well adjusted (as reported by parents, siblings, and teachers) also experiences more maternal closeness, more sibling friendliness, more peer friendliness, more say in family decision making, and more parental chore expectations as compared to the other sibling.     

Parenting and child behavioral adjustment in early childhood: a quantitative genetic approach to studying family processes

The aim of this study was to examine environmental and gene-environment processes linking parenting (i.e., affect, control, responsiveness) and preschool children's behavioral adjustment difficulties (e.g., noncompliance, conduct problems) by using bivariate genetic analyses of parents' and observers' ratings. The sample included 120 identical and same-sex fraternal twin pairs (M age = 43 months). Data sources included in-home observations, interviews, and parents' reports. Observers' ratings of children's difficult behaviors included shared and nonshared environmental variance. In contrast, parents' ratings of children's conduct problems showed genetic and nonshared environmental variance. Observer-rated maternal behavior included shared and nonshared environmental variance, although maternal responsiveness also included child genetic variance. Parent self-reported negative and positive affect included shared and nonshared environment as well as child genetic variance. There was no evidence for gene-environment interaction or dominance. Higher levels of difficult behavior and conduct problems covaried with higher levels of maternal negative affect and control and lower levels of maternal positive affect and control. Shared environmental mediation of these correlations was found for observations, whereas genetic and nonshared environmental mediation was found for parents' ratings. In general, estimates of shared environmental variance and mediation were greatest for observational data, and estimates of child genetic variance and mediation were greatest for parent-rated data. The implications of this pattern of findings for genetic research on family processes are discussed.     

The relationship between siblings’ college choices: Evidence from one million SAT-taking families

Recent empirical work has demonstrated the importance both of educational peer effects and of various factors that affect college choices. We connect these literatures by highlighting a previously unstudied determinant of college choice, namely the college choice made by one's older sibling. Data on 1.6 million sibling pairs of SAT-takers reveals that younger and older siblings’ choices are very closely related. One-fifth of younger siblings enroll in the same college as their older siblings. Compared to their high school classmates of similar academic skill and with observably similar families, younger siblings are about 15–20 percentage points more likely to enroll in 4-year colleges or highly competitive colleges if their older siblings do so first. These findings vary little by family characteristics. Younger siblings are more likely to follow the college choices of their older siblings the more they resemble each other in terms of academic skill, age and gender. We discuss channels through which older siblings’ college choices might causally influence their younger siblings, noting that the facts documented here should prompt further research on the sharing of information and shaping of educational preferences within families.     

Genetic and environmental components of adolescent adjustment and parental behavior: a multivariate analysis

Adolescent adjustment measures may be related to each other and to the social environment in various ways. Are these relationships similar in genetic and environmental sources of covariation, or different? A multivariate behavior-genetic analysis was made of 6 adjustment and 3 treatment composites from the study Nonshared Environment in Adolescent Development, using 674 same-sex adolescent sibling pairs aged 9-11. Cholesky decompositions of the total covariance matrix yielded additive and nonadditive genetic, and shared and nonshared environmental matrices. Factor analyses led to 3 factors for all but shared environment. The first 2 factors resembled Neuroticism and Extraversion factors typically found for personality; the third factor, parental monitoring and control, appeared to have different associations in different matrices.     

Genetic and Environmental Influences on Vocabulary IQ: Parental Education Level as Moderator

This article examines how parental education level moderates the genetic and environmental contributions to variation in verbal IQ. Data are from 1909 non-Hispanic Whites and African American sibling pairs from the National Longitudinal Study of Adolescent Health, which obtained nationally-based samples of identical (MZ) twins, fraternal (DZ) twins, full and half siblings, cousins (in the same household), and biologically unrelated siblings. In the whole sample, the variance estimate for heritability (h2 = .57, SE = .08) was greater than that for shared environment (c2 = .13, SE = .04). Both heritability and the shared environmental estimate were moderated, however, by level of parental education. Specifically, among more highly educated families, the average h2 = .74 (SE = .10) and the average c2 = .00 (SE = .05). Conversely, among less well-educated families, heritability decreased and shared environmental influences increased, yielding similar proportions of variance explained by genetic and environmental factors, average h2 = .26 (SE = .15), and average c2 = .23 (SE = .07).     

A Twin-Sibling Study of Observed Parent-Adolescent Interactions

Numerous behavioral genetic studies call attention to the strong and pervasive genetic influence on developmental characteristics. However, this research has been criticized for its use of poor environmental measures and a failure to examine the complex processes that are a hallmark of research in child development. This study addresses this criticism by examining the genetic and environmental components of parent-child interactions. Mother, father, and 2 adolescent siblings (10–18 years) from each of 675 families were observed interacting in 10-min dyadic problem-solving sessions. 6 groups of siblings that differed in genetic relatedness were examined (MZ and DZ twins, full siblings in nondivorced families; full, half, and unrelated siblings in stepfamilies). Results suggest a greater genetic component to adolescent behavior than to parent behavior. Both adolescent and parent behavior showed strong effects of nonshared environment, even after error of measurement was removed.     

Genetic and Environmental Influences on Temperament in Middle Childhood: Analyses of Teacher and Tester Ratings

Parent ratings of temperament in infancy and childhood yield evidence for genetic influence in twin studies but not in adoption studies. The present study used the sibling adoption design to investigate teacher and tester ratings of temperament in middle childhood. When each child was 7 years old, ratings on the Colorado Childhood Temperament Inventory were obtained from a teacher and tester for more than 50 pairs each of adoptive and nonadoptive siblings in the Colorado Adoption Project. Significant genetic influence emerged for both teacher and tester ratings of Activity, for tester ratings of Sociability, and for teacher ratings of Emotionality. Results obtained from bivariate genetic analysis suggest that the modest covariance between teacher and tester ratings of Activity is entirely mediated genetically. Except for teacher ratings of Attention Span, evidence of shared family environment was nonsignificant, despite the power of the sibling adoption design to detect it.     

Risk of maltreatment for siblings: Factors associated with similar and different childhood experiences in a dyadic sample of adult siblings

Siblings share the same environment and thus potentially a substantial number of risk factors for child maltreatment. Furthermore, the number of siblings and the sibling constellation itself might pose a risk for child maltreatment. Little is known about the likelihood that more than one child in a family is maltreated and which factors increase the risk. This study sought to investigate similarities and differences in maltreatment in siblings and risk factors associated with the maltreatment of more than one child from the same family. Data on maltreatment during childhood and adolescence, family background, and sibling constellation were collected from 870 pairs of siblings. In the dyadic analyses, siblings reported similar maltreatment experiences, especially when any type of maltreatment was considered. Parents’ mental health problems were significant predictors for maltreatment of at least one sibling. Father’s mental health problems were predictive of maltreatment of both or only the younger sibling, mother’s mental health problems of both or only the older sibling. Closeness in age and same gender of siblings did not emerge as a consistent predictor. The increasing number of siblings was a risk factor for any type of maltreatment of both siblings. The results highlight the need for preventive measures for families with a large number of children and with parents with mental health problems as well as a repeated risk assessment of all siblings in a family when one sibling was maltreated.     

Sibling Differences in Divorced Families

Sibling differences in family processes and individual adjustment were examined for 133 sibling pairs (10–18 years old) in divorced families. Although all siblings differed, siblings who lived apart after their parents' divorce differed more than siblings who lived together, contradicting past research that found negligible effects of shared environment on sibling similarities. The possibility that siblings might live apart because they were initially more different was considered. This hypothesis was not supported in the limited tests permitted by the data. Differences in family processes were associated with differences in adjustment for pairs who lived together as well as pairs who lived apart.     

A biometrical analysis of perceptions of family environment: a study of twin and singleton sibling kinships

Biometrical genetic analysis was applied to sibling and twin kinship data on 2 dimensions of perceived home environment. Correlations on 1 dimension, Restrictiveness-Permissiveness, were equal and significant for all kinships: MZ twins, DZ twins, same-sex siblings, and opposite-sex siblings significant for all 4 kinships: MZ twins, DZ twins, same-sex siblings, and opposite-sex siblings (r greater than .40). An E2-E1 biometrical model fitted Restrictiveness-Permissiveness, implying that treatments common to siblings create agreement about perceived environment. As intrapair differences were the same for all 4 kinships under this model, the equal environments assumption of the twin method was supported. In contrast, the Acceptance-Rejection dimension fitted a G-E1 model that makes the assumption that sibling similarity is the result of genetic factors and postulates an absence of shared environmental influences. This finding suggests that this aspect of home environment may depend as much on the child's inherited traits as on actual treatments and is in accord with the genetic analysis of individual traits in that developmentally effective environmental factors do not appear to be common to siblings.     

Perceived competence and self-worth during adolescence: a longitudinal behavioral genetic study

This investigation is the first longitudinal behavioral genetic study of self-concept during adolescence. It is a follow-up of a previous study examining genetic and environmental contributions to children's perceived self-competence and self-worth using a twin/sibling design. The study investigated adolescents' reports 3 years later and stability across two time points. Participants included 248 pairs of same-sex twins, full siblings, and stepsiblings between 10 and 18 years old. The results showed that six of the seven subscales were heritable at the second time point. None of the scales showed significant shared environmental effects. Longitudinal analyses revealed genetic contributions to stability for perceived scholastic competence, athletic competence, physical appearance, and general self-worth. Social competence, on the other hand, showed nonshared environmental mediation across time. These findings highlight the importance of genetically influenced characteristics and unique experiences as correlates of individual differences in self-concept during adolescence.