Household chaos is able to work in an additive way and predict children's problem behaviour over and above parenting, and is particularly potent when in combination with less positive/more negative parenting.

Measures of family environment often show substantial differences between children in the same family and are thus nonshared environment candidates. A key question is whether differential environments are related to differential outcomes when genetic differences between children in the same family are controlled. Parent and child reports and observations of family interactions were used to assess familial negativity and adolescents' depressive symptoms and antisocial behavior in a genetically informative sample of 719 same-sex sibling pairs ranging from 10 to 18 years old. Analyses revealed that parental and sibling negativity is significantly related to adolescent adjustment through nonshared environmental processes, although genetic factors account for most of the association between parental negativity and adolescent adjustment.One of the most interesting and important findings from the field of behavioral genetics concerns nurture rather than nature. Results from family, twin, and adoption studies converge on the conclusion that environmental influences on behavioral development operate in a nonshared manner, making children in the same family different from one another rather than similar, with only a few exceptions such as antisocial behavior (Plomin, Chipuer, & Neiderhiser, 1994;Plomin & Daniels, 1987). Family environment can be investigated as a source of nonshared environment by studying child-specific environments of siblings (Reiss, 1993). Such studies indicate that children in the same family experience surprisingly different environments .In the present study, the adjustment outcomes of interest were adolescent depressive symptoms and antisocial behavior. Rates of these problems that are quite stable during middle childhood increase over the course of adolescence (e.g., Lewin-

The overarching goal of the study was to identify links between sibling relationship quality in early/middle childhood with children's adjustment, having accounted for the effects of parent-child relationship quality. The sample consisted of 101 working and middle-class 2-parent English families with 2 children ages 4-8 years. Parents provided reports of sibling relationship quality, the parent-child relationship, and the children's prosocial and problematic behaviors. The children also provided reports of their familial relationships with a puppet interview. Results indicated that sibling relationship quality was associated with the older siblings' adjustment, controlling for the children's relationships with parents. In addition, the pattern of findings suggested that positivity within the sibling relationship was more strongly linked with child adjustment than was sibling conflict.

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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.

Using a longitudinal, large-scale sample of British twins, we addressed the prediction of both cognitive abilities and behavioral adjustment from eight domains of environmental risk: minority status, socio-economic status, maternal medical factors, twin medical factors, maternal depression, chaos within the home environment, and parental feelings towards their children and discipline. Participants included 5765 families with twins (49.1% male) born in 1994 and 1995. Aspects of environmental risk were assessed from birth until the children's third birthdays; outcome measures were assessed at their fourth birthdays. Overall prediction of outcome (via multiple regression analysis) was moderate (R = .23 -.48). SES and chaos were the strongest predictors for the cognitive outcomes whereas for total behavior problems the more proximal parenting factors were also dominant. Future analyses will investigate these environmental risk indicators in the context of the genetically sensitive twin design.Correspondence should be sent to Alison Pike, Psychology

The support for the cumulative hypothesis highlights the importance of having a broad picture of children's characteristics and environmental components when analysing children's adjustment. The distinct influence of risk stemming from the different ecological levels suggests that the trajectories of internalising, externalising and total problem behaviour may be different.

Behavioural genetic research has shown that environmental influences relevant to the development of individual differences are largely nonshared in origin. That is, environmental influences do not make children in the same family similar to one another, however, little is known about which specific aspects of the environment are responsible. Identical (MZ) twins provide a uniquely powerful tool to search for specific nonshared environmental influences independent of nonshared genetics because such twins do not differ genetically. The sample consisted of 93 MZ twin pairs aged 10-18 years from the Nonshared Environment and Adolescent Development (NEAD) project. Reports of parental negativity and adolescent adjustment were obtained from parents, ratings of videotaped observations, and the adolescents themselves. Relative differences of mothers' and fathers' negativity within MZ pairs correlated significantly with MZ differences in antisocial behaviour. The correlations were moderate for within-reporter associations, but were negligible for associations between reporters. Possible interpretations for these source-specific findings are discussed.