Effortful control is an important regulative dimension of temperament, which is associated with later internalizing and externalizing problems (Calkins & Dedmon, 2000; Eisenberg, Cumberland, et al., 2001; Lengua, 2006; Loukas & Roalson, 2006; Murray & Kochanska, 2002). It has been defined as “the ability to inhibit a dominant response to perform a subdominant response” (Rothbart & Bates, 1998, p. 137), and this ability is believed to emerge early and to have a constitutional, biological base. However, it could be modifiable by experience. Parenting is thought to be an important environmental experience for the socialization of effortful control. In previous research, children whose mothers displayed more negative affect or behaviors were more likely to exhibit lower levels of effortful control (Kochanska, Murray, & Harlan, 2000; Olson, Bates, & Bayles, 1990; Zhou, Eisenberg, Wang, & Reiser, 2004).

In these studies, parent-child pairs from different families were compared to each other. A methodological defect with such “between-families, one child per family” research design is that it confounds parenting effects with other factors that may vary between families (e.g., low social class, parental psychopathology). A more powerful approach is to use within-family design by sampling two children in the same family to control between-family variations, a design commonly used by sibling researchers (Conger & Conger, 1994; Daniels & Plomin, 1985; McHale & Pawletko, 1992). However, the confounding effects of age and gender cannot be completely ruled out in the within-family sibling design, as siblings differ in chronological age and may be of a different gender (Moffitt, Caspi, Rutter, & Silva, 2001; Rutter, Giller, & Hagell, 1998). Another limitation of research using the within-family sibling design is that it is unknown whether the association between parenting and children’s outcomes in the same family reflects an environmental effect or a genetic effect. An even more effective approach is to use monozygotic twins (MZ), who are not only reared in the same families, but are also identical in gender, age, and genetic makeup.

Since the 1980s, behavioral genetic researchers have shown that the largest environmental contributions to children’s outcomes occur at the child-specific (i.e., nonshared environment) level rather than at the family-wide (i.e., shared environment) level (Daniels & Plomin, 1985; Plomin & Daniels, 1987). However, traditional behavioral genetic studies have not measured specific nonshared experiences. MZ difference provides the most direct approach to uncover specific nonshared environment because such twins are identical in genetic makeup (Pike, Reiss, Hetherington, & Plomin, 1996; Plomin, DeFries, McClearn, & McGuffin, 2001). As such, linking between MZ twins’ differential experiences and differences in outcomes is an unambiguous, robust method to test environmental experiences because it rules out a genetic confounding effect (Caspi et al., 2004).

Researchers have begun to use this method to examine whether or not sibling differences in parental treatment are linked to child-specific behavior problems. For example, Caspi et al. (2004) showed that differences in antisocial behaviors between MZ twin siblings were at least partially traceable to differences in maternal expression of emotions. Pike et al. (1996) found that differences in parents’ negativity within adolescent MZ pairs correlated significantly with differences in antisocial behaviors of these two individuals.

However, most of the studies in which the MZ differences method was used were focused on antisocial behavior or externalizing behavior. This design was not generally expanded to other fields. The goal in this study was to examine whether or not specific poor maternal parenting is an environmental risk factor in the development of adolescents’ effortful control. We hypothesized that maternal harsh-inconsistency and hostility, as well as nurturance-involvement and warmth were possible elements of the nonshared environment associated with adolescents’ effortful control.

Method

Participants

Participants were 1,170 (590 male, 580 female) same-sex, reared-together MZ twins (585 pairs), aged from 11 to 18 years (M = 13.74, SD = 2.10), who were recruited from elementary and high schools randomly selected from all 18 counties or districts in the Beijing municipality. The participating adolescents were primarily of Han ethnic origin (about 92%). One parent of each participant was invited to participate in this study. In the present study, 64% of adolescent participants’ participating parents were mothers.

Procedure

Letters describing the study were distributed to the parents and the adolescents. Consent forms signed by both the adolescents and their parents were returned to teachers. Adolescents who consented to participate in the study were gathered in their classrooms after school time. After describing the purposes of the research and explaining the procedure, trained research staff firstly collected the twins’ saliva. Each child was asked to rinse his or her mouth with tap water and rest for about 5 minutes, and then provide 2 ml of whole saliva in a collecting tube labeled with their name and the collection time. After the collection of saliva, research staff distributed the questionnaire to the participants and instructed them to complete this. The questionnaire for parents was sent to the children’s homes. Participants were instructed to seal their questionnaires in the envelopes provided immediately after completing their responses. Researchers visited each school to collect the completed questionnaires. Confidentiality of the participants’ responses to the questionnaire was ensured. The Review Board of the Institute of Psychology at the Chinese Academy of Sciences in Beijing approved the research protocols.

Zygosity Determination

The zygosity of twins was confirmed by DNA test. The DNA was extracted from the saliva of each participant. Saliva has been found to be a reliable means of providing sufficient quantity and good quality DNA for genetic epide- miological studies, especially for twin research. This method of determination has an accuracy rate of 99.0% (Rogers, Cole, Lan, Crossa, & Demerath, 2007). Reliability and validity have been supported in a Chinese sample (Chen et al., 2010; Zhang & Ji, 2008).

Measures

Demographic information Participants reported their age, gender, and ethnicity. Mothers’ education was assessed with five categories: (1) elementary school, (2) junior high, (3) high school, (4) college, and (5) postgraduate degrees. The descriptive statistics indicated that 6.0% of mothers had only elementary school education, 34.3% of mothers completed junior high school, 29.9% mothers completed high school, 27.1% mothers graduated from college, and 2.7% mothers attained postgraduate qualifications.

Effortful control Adolescents and their participating parent rated adolescents’ effortful control using the Early Adolescent Temperament Questionnaire–Revised (Ellis & Rothbart, 2001) on a scale ranging from 1 (almost always untrue) through 5 (almost always true), which was developed to assess an individual’s capacity to voluntarily regulate behavior and attention. For the present data, the Cronbach’s alphas for the combined 15-item adolescent-reported and 17-item parent-reported effortful control scales were .74 and .76, respectively.

Maternal parenting Maternal parenting was assessed through scales adapted from the Iowa Youth and Families Project (Conger, Patterson, & Ge, 1995). Using a scale ranging from 1 (never) to 5 (always), adolescents rated items intended to measure four dimensions of their mothers’ parenting: nurturant-involved parenting, harsh-inconsistent parenting, maternal warmth, and hostility. Nurturant-involved parenting (12 items, α = .89) indicated the extent to which mothers knew about adolescents’ whereabouts and activities, as well as the degree to which mothers used reasoning and open communication with adolescents. Harsh-inconsistent parenting (7 items, α = .70) indicated the frequency with which mothers used harsh or inconsistent disciplinary practices. In addition to parenting behavioral dimensions, the affective dimensions of parenting were also assessed. Maternal warmth (6 items, α = .83), measured the frequency with which mothers expressed warmth and support toward their children. Maternal hostility (6 items, α = .85) indicated how often mothers expressed specific emotional negativity and anger toward their children. The constructs of nurturant-involved, harsh-inconsistent, maternal warmth, and maternal hostility parenting behaviors have been measured successfully in past studies (e.g., Brody et al., 2001; Simons, Whitbeck, Beaman, & Conger, 1994) and have been validated in a Chinese American adolescent sample (Kim & Ge, 2000).

Analytical Strategies

The MZ-difference method uses relative difference scores. That is, relative differences for environmental measures were created by subtracting Twin B’s environment score from Twin A’s environment score. Relative difference scores in outcome were also created by subtracting Twin B’s score on each outcome measure from Twin A’s score on the outcome.

Then, a regression approach was used to test whether or not the difference score in parenting in MZ related to a phenotypic difference score for effortful control. This can be represented as Y₁ - Y₂ = b₀ + b₁ (X₁ - X₂) + ε (Purcell & Koenen, 2005). In these analyses, we separately estimated the contribution of each parenting variable to avoid multicollinearity. We used multiple informants (adolescent and parent) to assess siblings’ effortful control and conducted regression analysis separately for each informant to avoid the effect of shared method variance.

Results

Intrapair correlations were firstly conducted to examine the differences and similarities in MZ twins’ effortful control and in how they were treated by mothers. The correlations between MZ twins in their effortful control are shown in Table 1. MZ twins were similar in their effortful control, especially from the viewpoint of their mothers. However, the genetically identical (MZ) twins were not phenotypically identical. Approximately one third to one half of the variance in the adolescents’ effortful control could be attributed to nonshared environmental effects (including measurement error) (1 - .44 = .56 according to adolescents’ ratings and 1 - .71 = .29 according to mothers’ ratings).

The significant cross-twin correlations of the maternal parenting measures indicated that there were both similarities and differences between MZ twins in the maternal treatment they received. This allowed for the possibility that differences in maternal parenting may account partially for the effortful control differences observed between twins.

Results generated from regression analyses are shown in Table 2. Differences in maternal nurturant-involved, or harsh-inconsistent parenting, warmth, and hostility were significantly related to sibling differences in adolescents’ reports of effortful control. Similar patterns of the results were obtained when parents’ reports of effortful control were used. These significant coefficients indicated that the adolescent who received more maternal nurturant-involved parenting and warmth, and less harsh-inconsistent parenting and hostility, had a higher level of effortful control than did his or her twin sibling.

Discussion

In this study it was found that maternal parenting was associated with adolescents’ effortful control. To our knowledge, this study is perhaps the first in which a genetically informative design with MZ-difference method has been used to demonstrate that unfavorable maternal parenting is an environmentally mediated risk factor for adolescents’ effortful control.

Parenting is thought to be an important environmental experience for the socialization of effortful control. Negative and punitive parenting, as well as negative expressivity, have been linked to lower levels of effortful control (e.g., Eisenberg, Gershoff, et al., 2001; Gartstein & Fagot, 2003), whereas positive parenting and parental expressions of positive emotions have been associated with higher effortful control (e.g., Eisenberg et al., 2005).

However, in studies in which the between-family design was used, the association between parenting and effortful control may be confounded by between-family variables. Moreover, such one-child-per-family studies may not eliminate out the possibility that the association between parenting and adolescents’ effortful control is genetically mediated. In this study, we ruled out these possibilities because the results documented that differences in maternal parenting were related to differences between genetically identical MZ twins who were reared in the same family.

Our finding was consistent with those of previous researchers who found that negative maternal parenting (harsh-inconsistent) and maternal negative expressivity (hostility) were linked to lower levels of effortful control, whereas positive maternal parenting (nurturance-involvement) and maternal expression of positive emotion (warmth) were associated with greater effortful control. Adolescents may be more motivated and better able to learn from supportive and warm mothers (Eisenberg et al., 2005). In contrast, the negative and punitive maternal parenting may produce affective overarousal in adolescents, which could undercut learning of self-regulation by compromising their attentional capacities (Hoffman, 2000).

In this study we used multiple sources of information in assessing adolescents’ effortful control. Problems associated with shared method variance are well known in family research (Bank, Dishion, Skinner, & Patterson, 1990). In this study, the results documented that maternal parenting was associated not only with adolescents’ own reports of their effortful control but also with parents’ reports of children’s effortful control. The consistency across informants provided a more robust support for parenting as the nonshared environment, which related with adolescents’ effortful control.

Two caveats of the study need to be noted. First, as with any cross-sectional study, causality can not be inferred from the observed associations. More longitudinal research is needed to further substantiate our findings. Second, our data were collected in China, and more research is necessary to determine whether our findings will be replicated in other populations.

Despite these limitations, this study provided a rare opportunity with a novel design for identifying the role of specific nonshared environment in adolescents’ effortful control. The results inform us that although effortful control may have a constitutional base, it may also be affected by environmental factors, such as parenting. Advantageous maternal behaviors (high level of maternal nurturance- involvement and warmth and low level of maternal harsh-inconsistence and hostility) would promote adolescents’ regulative ability.

Bank, L., Dishion, T., Skinner, M., & Patterson, G. (1990). Method variance in structural equation modeling: Living with “glop”. In G. R. Patterson (Ed.), Depression and aggression in family interaction (pp. 247-280). Hillsdale, NJ: Erlbaum.

Brody, G., Ge, X., Conger, R., Gibbons, F., Murry, V., Gerrard, M., et al. (2001). The influence of neighborhood disadvantage, collective socialization, and parenting on African American children’s affiliation with deviant peers. Child Development, 72(4), 1231-1246.

Calkins, S., & Dedmon, S. (2000). Physiological and behavioral regulation in two-year-old children with aggressive/destructive behavior problems. Journal of Abnormal Child Psychology, 28(2), 103-118.

Caspi, A., Moffitt, T., Morgan, J., Rutter, M., Taylor, A., Arsenault, L., et al. (2004). Maternal expressed emotion predicts children’s antisocial behavior problems: Using monozygotic-twin differences to identify environmental effects on behavioral development. Developmental Psychology, 40(2), 149-161.

Chen, J., Li, X., Chen, Z., Yang, X., Zhang, J., Duan, Q., et al. (2010). Optimization of zygosity determination by questionnaire and DNA genotyping in Chinese adolescent twins. Twin Research and Human Genetics, 13(2), 194-200.

Conger, K., & Conger, R. (1994). Differential parenting and change in sibling differences in delinquency. Journal of Family Psychology, 8(3), 287-302.

Conger, R., Patterson, G., & Ge, X. (1995). It takes two to replicate: A mediational model for the impact of parents’ stress on adolescent adjustment. Child Development, 66(1), 80-97.

Daniels, D., & Plomin, R. (1985). Differential experience of siblings in the same family. Developmental Psychology, 21(5), 747-760.

Eisenberg, N., Cumberland, A., Spinrad, T., Fabes, R., Shepard, S., Reiser, M., et al. (2001). The relations of regulation and emotionality to children’s externalizing and internalizing problem behavior. Child Development, 72(4), 1112-1134.

Eisenberg, N., Gershoff, E., Fabes, R., Shepard, S., Cumberland, A., Losoya, S., et al. (2001). Mothers’ emotional expressivity and children’s behavior problems and social competence: Mediation through children’s regulation. Developmental Psychology, 37(4), 475-490.

Eisenberg, N., Zhou, Q., Spinrad, T., Valiente, C., Fabes, R., & Liew, J. (2005). Relations among positive parenting, children’s effortful control, and externalizing problems: A three-wave longitudinal study. Child Development, 76(5), 1055-1071.

Ellis, L., & Rothbart, M. (2001). Revision of the Early Adolescent Temperament Questionnaire. Paper presented at the Society for Research in Child Development, Minneapolis, MN, USA.

Gartstein, M., & Fagot, B. (2003). Parental depression, parenting and family adjustment, and child effortful control: Explaining externalizing behaviors for preschool children. Journal of Applied Developmental Psychology, 24(2), 143-177.

Hoffman, P. (2000). Empathy and moral development: Implications for caring and justice. New York: Cambridge University Press.

Kim, S., & Ge, X. (2000). Parenting practices and adolescent depressive symptoms in Chinese American families. Journal of Family Psychology, 14(3), 420-435.

Kochanska, G., Murray, K., & Harlan, E. (2000). Effortful control in early childhood: Continuity and change, antecedents, and implications for social development. Developmental Psychology, 36(2), 220-232.

Lengua, L. (2006). Growth in temperament and parenting as predictors of adjustment during children’s transition to adolescence. Developmental Psychology, 42(5), 819-832.

Loukas, A., & Roalson, L. (2006). Family environment, effortful control, and adjustment among European American and Latino early adolescents. Journal of Early Adolescence, 26(4), 432- 455.

McHale, S., & Pawletko, T. (1992). Differential treatment of siblings in two family contexts. Child Development, 63(1), 68-81.

Moffitt, T., Caspi, A., Rutter, M., & Silva, P. (2001). Sex differences in antisocial behaviour: Conduct disorder, delinquency, and violence in the Dunedin longitudinal study. Cambridge, UK: Cambridge University Press.

Murray, K. T., & Kochanska, G. (2002). Effortful control: Factor structure and relation to externalizing and internalizing behaviors. Journal of Abnormal Child Psychology, 30(5), 503-514.

Olson, S., Bates, J., & Bayles, K. (1990). Early antecedents of childhood impulsivity: The role of parent-child interaction, cognitive competence, and temperament. Journal of Abnormal Child Psychology, 18(3), 317-334.

Pike, A., Reiss, D., Hetherington, E., & Plomin, R. (1996). Using MZ differences in the search for nonshared environmental effects. Journal of Child Psychology and Psychiatry, 37(6), 695-704.

Plomin, R., & Daniels, D. (1987). Why are children in the same family so different from one another? Behavioral and Brain Sciences, 10(1), 1-16.

Plomin, R., DeFries, J., McClearn, G., & McGuffin, P. (2001). Behavior genetics. New York: Worth.

Purcell, S., & Koenen, K. (2005). Environmental mediation and the twin design. Behavior Genetics, 35(4), 491-498.

Rogers, N., Cole, S., Lan, H., Crossa, A., & Demerath, E. (2007). New saliva DNA collection method compared to buccal cell collection techniques for epidemiological studies. American Journal of Human Biology, 19(3), 319-326.

Rothbart, M., & Bates, J. (1998). Temperament. In W. Damon & N. Eisenberg (Eds.), Handbook of child psychology: Social, emotional, and personality development (Vol. 3, pp. 105-176). New York: Wiley.

Rutter, M., Giller, H., & Hagell, A. (1998). Antisocial behavior by young people. New York: Cambridge University Press.

Simons, R., Whitbeck, L., Beaman, J., & Conger, R. (1994). The impact of mothers’ parenting, involvement by nonresidential fathers, and parental conflict on the adjustment of adolescent children. Journal of Marriage and the Family, 56(2), 356-374.

Zhang, Y., & Ji, C. (2008). An application of salivary DNA in twin research of Chinese children. Twin Research and Human Genetics, 11(5), 546-551.

Zhou, Q., Eisenberg, N., Wang, Y., & Reiser, M. (2004). Chinese children’s effortful control and dispositional anger/frustration: Relations to parenting styles and children’s social functioning. Developmental Psychology, 40(3), 352-366.

One author

Dr. Xiaojia Ge

passed away while this study was being conducted. The other authors want to express their endless respect for him. This study was funded by the Chinese Academy of Sciences innovation program (KX05-066)

funds for young scholars of the Institute of Psychology

Chinese Academy of Sciences (O7CX071007)

and the National Natural Science Foundation of China (30600183).

Appreciation is due to reviewers including

Gunnar Bjø

rnebekk

The Norwegian Centre for Studies of Conduct Problems and Innovative Practice

University of Oslo

Norway

Email

[email protected]

Zhengyan Wang

Capital Normal University

Beijing

People&rsquo

s Republic of China

[email protected]">[email protected]

Zhiyan Chen, Key Lab of Mental Health, Institute of Psychology, Chinese Academy of Sciences, 4A Datun Road, Chaoyang District, Beijing, People’s Republic of China 100101. Phone: +86-10-64845636; Fax: +86-10-64881329; Email: [email protected]