Developmental Psychology 2015, Vol. 51, No. 4, 489 – 499

© 2015 American Psychological Association 0012-1649/15/$12.00 http://dx.doi.org/10.1037/a0038800

Infant Risk Factors Associated With Internalizing, Externalizing, and Co-Occurring Behavior Problems in Young Children Renee C. Edwards and Sydney L. Hans

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The University of Chicago The purpose of the current study was to examine the unique and interactive contributions of infant negative emotionality and family risk factors in the development of internalizing-only, externalizingonly, and co-occurring behavior problems in early childhood. The sample included 412 infants and their primary caregivers. Interviews and temperament assessments took place when infants were 5–7 months old, and primary caregivers completed child behavior ratings at ages 2 1/2 and 5 years. Mixed-effects multinomial logistic regression was used to examine associations between infant risk factors and “pure” and co-occurring child behavior problems, and test whether these associations changed over time. The results of this study showed that hostile parenting during infancy increased the likelihood that children would develop internalizing-only problems, whereas infants who were highly distressed in response to novelty were at increased risk of developing externalizing-only problems. Multiple risk factors, including maternal anxious and depressive symptoms, family conflict, and younger maternal age, independently predicted early childhood co-occurring problems. Additionally, there was a significant interaction between infant anger/frustration and hostile parenting: In the context of hostile parenting, infants high in anger were at increased risk of developing early co-occurring problems, though this association faded by age 5. These findings point to the importance of considering the infant’s family context, and differentiating between “pure” and co-occurring behaviors when examining the etiology of early childhood behavior problems. Keywords: co-occurring behavior problems, internalizing, externalizing, temperament, infant risk factors

child is first engaging with his parents and family environment (Côté et al., 2009; Lahey et al., 2008). Further exploration of infant predictors of early behavior problems is important to better understand the developmental origins, but also to potentially inform the design and targeting of interventions to prevent problem behavior. Preventive interventions that begin during the first years of life may be particularly effective as patterns of parenting and child behavior are emerging and may be easier to modify.

Strong evidence suggests that mental health problems can emerge in the first years of life (Briggs-Gowan, Carter, BossonHeenan, Guyer, & Horwitz, 2006; Wilens et al., 2002) and that early socioemotional and behavioral problems are often part of the developmental course toward mental health problems in childhood and adolescence (Fanti & Henrich, 2010; Feng, Shaw, & Silk, 2008). Characteristics of both child and environment, independently and in interaction with each other, seem to contribute to the development of early behavior problems (e.g., Campbell, Shaw, & Gilliom, 2000; Mills et al., 2012). Although much research has focused on risks for early externalizing problems and, to a lesser extent, internalizing problems, few studies have differentiated young children with internalizing-only, externalizing-only, and co-occurring problems, and investigated whether there are infant risk factors specific for each type of problem. Notably, the literature suggests that risks for young children’s behavior problems may be present as early as infancy when the

Co-Occurring Internalizing and Externalizing Behaviors While some young children exhibit only internalizing behaviors, such as sadness, anxiety, and withdrawal, or only externalizing behaviors, such as aggression and defiance, it is also common for young children to exhibit co-occurring problems (Briggs-Gowan et al., 2006; Wilens et al., 2002). Research suggests that the cooccurrence of internalizing and externalizing problems is a distinct syndrome and can emerge very early in life (Angold, Costello & Erkanli, 1999; Fanti & Henrich, 2010; Keiley, Lofthouse, Bates, Dodge, & Pettit, 2003). Persistence in behavior problems may be especially strong for young children with co-occurring problems (Briggs-Gowan et al., 2006). Multiple child and family risk factors may precede the development of co-occurring problems (see Oland & Shaw, 2005), and children with co-occurring problems are at especially high risk for experiencing adverse outcomes (Fanti & Henrich, 2010; Yoo, Brown, & Luthar, 2009). However, with the exception of a recent study by Fanti and Henrich (2010), little is known about the etiology of co-occurring problems in very young children.

This article was published Online First February 9, 2015. Renee C. Edwards and Sydney L. Hans, School of Social Service Administration, The University of Chicago. We thank Robert Gibbons and the Center for Health Administration Studies at the University of Chicago for statistical consultation, Kate Keenan and Yoonsun Choi for assistance on initial drafts, and Anne Strohm for providing details on study design. Correspondence concerning this article should be addressed to Renee C. Edwards, The University of Chicago, School of Social Service Administration, 969 E. 60th Street, Chicago, IL 60637. E-mail: rcduffy@ uchicago.edu 489

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Family Risk Factors for the Development of Early Behavior Problems

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Whereas many environmental contexts shape the behavior of older children, including home, school, peers, and community, the family is the primary environmental context for most infants and has the best documented impact on infant emotional and behavior development. This study attempts to capture a set of family characteristics that may be particularly influential during infancy and are known to predict behavior problems in later developmental periods.

Hostile Parenting Longitudinal studies have shown that hostile, controlling parenting of toddlers is related to internalizing and externalizing problems (Campbell, Shaw, & Gilliom, 2000; Feng et al., 2008; Gilliom & Shaw, 2004). Young children experiencing hostility may lack opportunities to learn to regulate their fearful emotions in an adaptive manner, struggle with feelings of low efficacy and anxiety, and withdraw socially (Rubin & Mills, 1991; Wood, McLeod, Sigman, Hwang, & Chu, 2003). Hostile parenting can also exacerbate defiance and aggression in toddlers as their need for autonomy emerges (Campbell et al., 2000). In one study, harsh parenting in 4 –5 year olds predicted both externalizing and cooccurring problems in school-age children (Keiley et al., 2003), but more research is needed to test whether hostile parenting observed during infancy is associated with later “pure” and/or co-occurring problems.

Maternal Depression and Anxiety Maternal depression and anxiety during infancy is a known risk factor for the development of behavior problems (Bureau, Easterbrooks, & Lyons-Ruth, 2009; Goodman et al., 2011). Children may inherit a genetic predisposition to depression (Lesch, 2004), and depression/anxiety can impact mother– child interactions (Lovejoy, Graczyk, O’Hare, & Neuman, 2000). Mothers with depression may become intrusive or disengage during interactions; they display negative emotions more frequently; and are less responsive to infants’ positive affect (Field, Healy, Goldstein, & Guthertz, 1990). Infants of depressed mothers show more negative emotions and have difficulty self-regulating (Field et al., 1990). A meta-analysis showed that the effects of maternal depression are similar in magnitude for child internalizing and externalizing (Goodman et al., 2011), and Fanti and Henrich (2010) found that postpartum depression was associated with both “pure” and cooccurring problems in early childhood.

Family Conflict Family and marital conflict can also put children at risk for developing both internalizing and externalizing problems (see Davies & Cummings, 1994). Children who are exposed to chronic marital conflict may be in a heightened state of arousal and develop feelings of emotional insecurity, which in turn can lead to adjustment problems (Davies & Cummings, 1994; El-Sheikh, Cummings, Kouros, Elmore-Staton, & Buckhalt, 2008). Angry or violent conflicts are highly related to emotional distress, and marital conflict has been linked to poor child emotional regulation

(Crockenberg, Leerkes, & Lekka, 2007; Davies & Cummings, 1994). Essex, Klein, Cho, and Kraemer (2003) found that marital conflict during infancy was associated with elevated co-occurring internalizing and externalizing symptoms in kindergarten.

Family Socioeconomic Status (SES) Low family SES has been associated with internalizing and externalizing problems in very young children (Rijlaarsdam et al., 2013), and may put children at especially high risk for cooccurring problems (Fanti & Henrich, 2010; Keiley et al., 2003). Low income families often face numerous adversities that can exacerbate family stress and negatively impact parenting (Conger & Conger, 2002). Impoverished families also struggle to provide high-quality learning materials and other material goods that may foster positive child development (Yeung, Linver, & BrooksGunn, 2002). Risk factors within families are often interrelated and, due to limited etiological research measuring a variety of family factors, it is unclear whether the aforementioned risks uniquely predict “pure” and co-occurring problems in very young children. Interrelated risk factors may have independent effects, or influence child development through complex mechanisms in which more distal social or parent psychological factors contribute to proximal risk factors directly experienced by the infant. For example, because family conflict and maternal depression often co-occur it may be that one adversity explains the effects of the other on child behavior (Goodman & Gotlib, 1999), although Essex et al. (2003) found that early exposure to either risk factor was predictive of co-occurring symptoms. It is also known that maternal depression can impact parenting behaviors, including hostility, but depression may uniquely predict behavior problems through genetic transmission (Lesch, 2004) or impaired fetal development (e.g., Field, 2011). Low SES might operate primarily through the infant’s relationships with family, but other implications of SES, such as overall stress, physical conditions, or stimulation in the environment, could also be contributing factors independent of proximal family processes. By simultaneously considering a set of family adversities, this study aims to identify unique risks associated with behavior outcomes, which will (a) serve as a starting point for examining more complex relationships, and (b) illuminate potential entry points for early intervention efforts.

Infant Negative Emotionality (NE) and NE by Environment Interactions Negative Emotionality Prospective studies have shown that infant negative emotionality (NE), or difficult temperament, predicts early childhood internalizing and externalizing problems (Côté et al., 2009; Lahey et al., 2008; Shaw, Keenan, Vondra, Delliquadri, & Giovannelli, 1997). Infants high in NE are fussy, difficult to soothe, and respond to limitations and novelty with intense negativity. During infancy, NE involves two primary components, anger/frustration and fearfulness (Rothbart, Sheese, & Conradt, 2009). Infants who exhibit high levels of fear and distress to novelty are more likely to express fear, behavioral inhibition and internalizing problems throughout childhood (Kagan & Snidman, 2004; Putnam & Stifter,

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INFANT RISKS FOR CO-OCCURRING PROBLEMS

2005). Anger or frustration in response to limitations has been associated with later externalizing problems, and in some studies has predicted internalizing problems (Gartstein, Putnam, & Rothbart, 2012). Infant difficult temperament has also predicted cooccurring problems in childhood (Fanti & Henrich, 2010), but whether the fear/distress to novelty or anger/frustration aspect of infant NE links more closely with co-occurring problems remains to be tested. Vulnerability models of psychopathology suggest that some children may be more liable to the effects of adverse environmental conditions due to intrinsic “vulnerability” characteristics (Ingram & Price, 2010). NE has been identified as one such vulnerability factor: Children high on NE may be more likely than other children to develop emotional and behavioral problems when exposed to negative parenting and other environmental stressors (Belsky, Hsieh, & Crnic, 1998). Thus, the combination of infant NE and hostile parenting, maternal anxiety/depression, family conflict, or low SES, may confer the greatest risk for early childhood behavior problems. In the context of hostile parenting, infants high on NE may experience increased inhibition or frustration rather than learning to cope with stress, and evidence suggests that the combination of hostile, controlling parenting and toddler NE is related to later internalizing and externalizing problems (Feng, Shaw, & Silk, 2008; Gilliom & Shaw, 2004). Maternal depression may be less problematic for infants with “easy” temperaments because they are more resistant to stress and have more flexible coping strategies, but while some studies have found a stronger association between early NE and child depression in the context of maternal depression (Marakovitz, Wagmiller, Mian, Briggs-Gowan, & Carter, 2011), other research has not found evidence for interaction effects (Côté et al., 2009). Finally, infants high on NE may be more vulnerable to the effects of family conflict and adversity because they are more reactive to negative events and have less adaptive was of coping (Davies & Cummings, 1994), but again the empirical evidence is mixed (Marakovitz et al., 2011; Martinez-Torteya, Bogat, von Eye, & Levendosky, 2009; Pauli-Pott & Beckman, 2007; Shaw et al., 1997). Research on early co-occurring problems has not focused on NE as a vulnerability factor or examined NE by family environment interactions. Therefore, it is largely unknown whether highly frustrated or fearful infants exposed to various environmental stressors may be at specific risk for internalizing-only, externalizing-only, or co-occurring behavior problems.

Summary of Current Study The purpose of this longitudinal study was to investigate the unique and interactive contributions of infant NE and the infant’s family environment in the development of pure and co-occurring behavior problems at ages 2 1/2 and 5 years. Using mixed-effects multinomial logistic regression (MLR), we tested for specificity in infant risk factors and examined whether associations between risk factors and behavior problems varied over time. We hypothesized: Hypothesis 1: Hostile parenting, maternal anxious/depressive symptoms, family conflict, and low SES would be independent risk factors for each of the three problem behavior outcomes. We also anticipated that higher levels of these risk

491

factors would put infants at greater risk for developing cooccurring problems compared to internalizing-only or externalizing-only problems. Hypothesis 2: Infant distress to novelty was expected to predict internalizing-only problems, while infant anger/ frustration was expected to predict externalizing-only problems when considering the two components of NE simultaneously. Because NE has also been associated with co-occurring problems, we explored whether the components of infant NE (distress to novelty and anger/frustration) predicted early childhood co-occurring problems. Hypothesis 3: Finally, we hypothesized that highly distressed/ fearful infants and angry/frustrated infants would be more adversely affected by family stressors. However, given how little is known about temperament by environment interactions in the development of “pure” versus co-occurring problems, we approached these interactions in an exploratory manner.

Method Sample This investigation uses data from The Project on Human Development in Chicago Neighborhoods, Infant Assessment Unit (PHDCN IAU; Earls, Brooks-Gunn, Raudenbush, & Sampson, 2005). PHDCN is a longitudinal study designed to examine how individuals, families, schools, and neighborhoods impact human development. Over 6,000 participants across seven age cohorts were sampled from 80 out of 343 Chicago neighborhood clusters (NCs). The 80 NCs were sampled in an effort to reduce confounding of race and socioeconomic status (for details on sampling, see Sampson, Raudenbush, & Earls, 1997). The Infant Assessment Unit (IAU) sample included 412 infants and their primary caregivers selected from the 1,261 families enrolled in the birth cohort. The IAU sample participated in evaluations of infant temperament, parenting, maternal and infant health, and maternal mental health, in addition to measures administered to all subjects in the birth cohort. Families were interviewed and observed in their homes when infants were 5 months old (M ⫽ 5.1, SD ⫽ 2.7). Follow-up interviews were conducted when the children were 2 1/2 and 5 years old. The IAU sample included 217 male (52.7%) and 195 female (47.3%) infants. The primary caregivers for 98.8% of the infants were the biological mothers, so are referred to as “mothers.” Mothers were 27.1 years of age (SD ⫽ 7.1) on average at Wave 1 (infancy). Slightly over half (53.7%) were married, and 59% had at least a high school degree. The mean per capita income (1995– 1996 dollars) was $6,172 and ranged from $385 to $22,500. 40% of families received some type of public assistance; 33.5% of infants were the first born in their families. Roughly half of the infants were Latino/Hispanic (52.3%), 26.9% were African American/Black, 16.9% were Caucasian/ White, and the remaining group (3.9%) included infants of Asian, Pacific Islander, Native American and other backgrounds. English was the primary language spoken by 55.9% of the mothers, 31.4% spoke Spanish, 6.8% spoke English and another language, and 6% spoke a language other than English or Spanish with their infants.

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Eighty percent (n ⫽ 331) of families participated at Wave 2 (age 2 1/2), and 76% (n ⫽ 312) participated at Wave 3 (age 5). Attrition at Wave 2 was unrelated to income, mother age, child ethnicity, or mother marital status. Wave 3 attrition was unrelated to these factors, except mother age, or to behavior classification at age 2 1/2. Mothers who participated at Wave 3 were slightly older (M ⫽ 27.5 years, SD ⫽ 7.4) than mothers who left the study (M ⫽ 25.8 years, SD ⫽ 6.2; t(410) ⫽ 1.97, p ⫽ 05). Child mean age was 2.4 years (SD ⫽ .56) at Wave 2 and 4.9 years (SD ⫽ .48) at Wave 3.

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Measures Demographic measures. A small set of demographic variables was selected as possible covariates based on research suggesting associations with child behavior problems. This data, collected during infancy, included infant age, sex, preterm birth, birth order, hours of child care per week, and maternal age. Infant race/ethnicity was highly confounded with SES, one of the primary predictor variables, and so could not be included in the same analyses. Infant distress to novelty. When infants were 7 months old (M ⫽ 7.1, SD ⫽ 2.0), the Kagan Mobile Task was administered to assess infant behaviors in response to novel visual stimuli and toys (Kagan, Reznick, & Snidman, 1987). In this procedure, conducted in the family’s home, the mother was first asked to buckle her infant into a car seat and sit next to the infant for 1 min without speaking. The mother was then instructed to leave the view of the infant, and the infant was presented with novel toys hanging from a mobile for 3 min. The procedure was videotaped and the total number of frets and cries was recorded. Previous studies have demonstrated high interrater reliability, and predictive validity, such that infants who show high frequencies of irritability (crying and fretting) and activity show higher levels of fear, inhibition, anxiety, and social withdrawal at later ages (Kagan et al., 1999; Stern, Arcus, Kagan, Rubin, & Snidman, 1995). Coding was supervised by Dr. Snidman and Dr. Kagan. Infant anger and frustration. The Infant Behavior Questionnaire (IBQ) is a parent report measure designed to evaluate temperament in infants during the first year of life (Rothbart, 1981). In this study, mothers completed items on the distress to limitations subscale. This subscale included 11 items regarding the infant’s mood and behavior (fussing, crying, frustration while waiting or being confined) during regular activities, such as bathing, feeding, sleeping, and playing (␣ ⫽ .69). High convergent validity and moderate stability for the IBQ has been shown (Rothbart, 1986). Hostile parenting. The Home Observation for Measurement of the Environment (HOME) is an observational measure intended to capture multiple aspects of a child’s environment, including parenting behaviors (Caldwell & Bradley, 1984). Research assistants interviewed mothers, observed the infants and mothers in their homes, and completed a modified version of the InfantToddler HOME (IT-HOME). Five items comprised the lack of hostility subscale, including “parent does not shout at child,” “parent does not express annoyance with or hostility toward the child,” “parent neither slaps nor spanks child,” “parent does not scold or criticize child,” and “parent reports no physical punishment.” Researchers recorded whether they observed each behavior during the home visit (“yes” or “no”), and items were reverse coded to measure “hostile parenting” (␣ ⫽ .91).

Maternal anxious and depressive symptoms. The Young Adult Self Report (YASR; Achenbach, 1997) is 110 item selfreport questionnaire used to assess behavior problems in young adults. Mothers completed the YASR during the infant assessment. They responded to each item with a “0” if not true, “1” if somewhat or sometimes true, and “2” if very true or often true over the past 6 months. Achenbach (1997) has reported good validity and reliability for this measure. In the current study, the anxious/ depressed subscale was used in all analyses (␣ ⫽ .83). Family conflict. Family conflict was measured during the infant assessment using the conflict subscale from The Family Environment Scale (FES Real Form; Moos & Moos, 1994), a scale designed to assess the social/emotional climate of a family from the perspective of the family. The conflict subscale consists of nine true or false items that assess openly expressed anger and conflict in the family, such as “members of the family get so angry they throw things” (␣ ⫽ .72). The test–retest reliabilities have been shown to be greater than .70, and alpha coefficients are generally high (Moos & Moos, 1994). Family SES. Information on the mother’s and her partner’s educational levels, occupations, and salaries were collected during the infant assessment. The principal component of these three variables, highest education level, highest socioeconomic index for occupation, and household income was used as the composite family SES (Sampson et al., 1997). Child behavior problems. The PHDCN used items from the Child Behavior Checklist (CBCL)/2–3 (Achenbach, 1992), and the CBCL/4 –18 (Achenbach, 1991), which were completed by the mothers of the children at ages 2 1/2 and 5 years respectively. Parents respond “not true,” “somewhat or sometimes true,” and “very true or often true” to statements regarding the child’s behavior and emotions. The CBCL includes internalizing and externalizing scores, and has cutpoints for borderline (93rd percentile) and clinical levels (98th percentile) of behavior problems. In the present study, the internalizing subscale consisted of nine items at age 2 1/2 years (␣ ⫽ .58), and 31 items at age 5 years (␣ ⫽ .83). The externalizing subscale consisted of 10 items at 2 1/2 years (␣ ⫽ .79) and 22 items at 5 years (␣ ⫽ .85). At each follow-up age, children were classified as having “no problem behaviors,” “internalizing problems only,” “externalizing problems only,” and “co-occurring internalizing and externalizing problems” based on the nature of their CBCL scores. Children who fall at or above a T score (standardized score) of 60 on internalizing or externalizing problems are considered to be in the borderline clinical or clinical range (Achenbach, 1991). In this study only T scores at age 5 were able to be computed, because a reduced number of CBCL items were used at age 2 1/2. At age 5, a T score of 60 corresponded to a sample z-score of .75. Therefore, in order to estimate borderline and clinical levels when the children were 2 1/2 years old, internalizing and externalizing z-scores were calculated at each age. Z-Scores of .75 were used to approximate cutoff scores for “borderline clinical or clinical” problems. Children were then classified as having one of the four behavior types at each age based on these scores. For example, a child who had a z-score of 1.2 on internalizing behaviors and a z-score of 0.5 on externalizing behaviors at age 2 1/2 was classified as having “internalizingonly” problems.

INFANT RISKS FOR CO-OCCURRING PROBLEMS

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Data Analysis Because infant distress to novelty was positively skewed, a natural log transformation was applied. Hostile parenting was also highly skewed, with most mothers displaying no hostility, and so a dichotomous measure was created. Mothers who were observed to show any hostility toward their infants (i.e., received a “no” on at least one of the five “lack of hostility” items) were coded “1” for hostility and mothers who received a “yes” on all five items were coded “0.” All continuous temperament and environmental variables were mean centered in order to improve interpretability of coefficients and prevent multicollinearity between variables and interaction terms. The following interactions were then computed: Infant Distress to Novelty ⫻ Hostile Parenting, Distress to Novelty ⫻ Maternal Anxious/ Depressive Symptoms, Distress to Novelty ⫻ Family Conflict, Distress to Novelty ⫻ SES, Infant Anger ⫻ Hostile Parenting, Anger ⫻ Maternal Anxious/Depressive Symptoms, Anger ⫻ Family Conflict, and Anger ⫻ SES. Associations between demographic variables (infant age, infant sex, whether the child was first born, premature birth, hours of child care, and maternal age), risk factors (temperament and environmental measures), and behavior problem classifications at ages 2 1/2 and 5 were examined. Demographic variables that were found to be significantly associated with one or more risk factors and outcomes at either age were included as control variables in all models. Mixed-effects multinomial logistic regression (MLR; Hedeker & Gibbons, 2006) was used to examine associations between infant risk factors and longitudinal behavior group classifications. Mixed-effects regression models take into account hierarchical structures within the data, in this case repeated observations of problem behavior classification that are likely correlated across the two time points. In mixed-effects MLR, random-effects and fixed effects can be estimated, and comparisons can be made between each of the outcome categories. MLR models allow the examination of a dependent variable that has multiple categories. With four outcome categories (no problems, internalizing-only, externalizing-only, and co-occurring problems), three regression functions were estimated to compare each outcome to a reference group. Separate random-effects variances were estimated for each of the three comparison groups. SuperMix 1.1 (Hedeker, Gibbons, du Toit, & Cheng, 2008) was used to estimate models. Adaptive quadrature with 10 quadrature points was used as the optimization method. Most infant variables had few missing data except infant distress to novelty, which had 19% missing. Although missing outcome data can be handled within maximum likelihood estimation, subjects missing data on predictors would be excluded from the analyses. Therefore, Multiple Imputation (MI), using Stata 11.0 (Statacorp, 2009), was performed to address missing data on infant variables. Twenty imputed datasets were created using a Monte Carlo Markov Chain model. A sequential chain of 2,000 iterations was run, with imputations drawn every 100 iterations. Auxiliary variables were used to reduce any biases that may have resulted if infant data was missing not at random (MNAR; Collins, Schafer, & Kam, 2001). Auxiliary variables related to missingness or to variables with missing data, and all interaction terms planned for the analyses were included in the imputation process (von Hippel,

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2009). Once MI was complete, each missing value on a predictor variable was replaced by the mean of the 20 imputed values for that particular subject. Data from all subjects (n ⫽ 412) was then used for subsequent analyses. Three random intercept models were estimated to evaluate our study hypotheses. In order to examine unique family effects on problem behavior outcomes (Hypothesis 1), family risk factors and covariates were entered simultaneously into the first model. Because behavior outcomes were measured at two time points, this model also included time, and interactions between family risk factors and time. Time was coded as 0 (age 2 1/2) and 1 (age 5). Risk factor by time interaction terms were included to test whether there were changes over time in associations between infant risk factors and behavior group classification. The main effect of a risk factor indicates the effect at age 2 1/2, and a significant predictor by time interaction suggests a significant change in the association between the risk factor and behavior outcome from age 2 1/2 to age 5 (e.g., the association became stronger or weaker over time). The second model included only infant anger/frustration, infant distress to novelty, and temperament by time interaction terms in order to evaluate main effects of infant temperament (Hypothesis 2). In order to keep the final model parsimonious given the large number of variables and the moderate sample size, temperament by environment interactions were first tested individually (along with lower order terms and covariates) in separate MLR models for age 2 1/2 and age 5 outcomes. Significant interactions were then added to covariates, family risks, temperament, time, and predictor by time interactions in a third mixed-effects model (Hypothesis 3). The mixed-effects MLR models were rerun using different behavior group categories as the reference group so all pairwise comparisons of interest could be made. Odds ratios were used to make comparisons between each of the four behavior groups.

Results Descriptive Statistics and Preliminary Analyses Table 1 displays descriptive statistics and correlations among infant risk factors. At age 2 1/2, 9% (n ⫽ 27) of the children were classified as having “internalizing-only” problems, 9% (n ⫽ 29) exhibited “externalizing-only” problems, 14% (n ⫽ 45) fell into the “co-occurring” group, and 68% (n ⫽ 215) showed “no problem behaviors.” At age 5, 67% (n ⫽ 206) were classified as having “no problem behaviors,” and roughly 11% fell into each of the problem groups: “internalizing-only” (n ⫽ 34), “externalizing-only” (n ⫽ 33), and “co-occurring” problems (n ⫽ 35). 51% of children who fell into one of the three problem behavior groups at age 2 1/2 continued to have behavior problems at age 5. Specifically, 31% of children with internalizing-only, 55% of children with externalizing-only, and 64% of children with co-occurring problems at age 2 1/2 were classified into one of the problem behavior groups at age 5. Descriptive statistics for infant risk factors are shown separately for each of the behavior groups at each age in Table 2. Maternal age was associated with child behavior classifications and so was used as a covariate. Results of MLR models

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Table 1 Descriptive Statistics and Correlations Among Infant Risk Factors Infant risk factors 1. Infant anger/frustration 2. Infant distress to novelty 3. Hostile parenting 4. Maternal anxious/depressive symptoms

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5. Family conflict 6. Family SES

M (SD)

1

6.28 (3.08) n ⫽ 411 5.58 (9.46) n ⫽ 332 yes: 21.6% no: 78.4% n ⫽ 408 9.66 (5.93) n ⫽ 403 2.69 (2.19) n ⫽ 393 ⫺.11 (1.44) n ⫽ 402

1.00

examining temperament by environment interactions showed that Infant Anger ⫻ Hostile Parenting interaction was significantly associated with behavior classification at age 2 1/2 and so was included in the final mixed-effects MLR analysis. All other temperament by environment interactions were nonsignificant.

Mixed-Effects Multinomial Logistic Regression Analyses Hypothesis 1. Results of the first mixed-effects MLR model (see Table 3) showed that hostile parenting during infancy increased the likelihood that children would develop internalizingonly problems compared to no problem behaviors. Nonsignificant Predictor ⫻ Time interactions (e.g., Hostile Parenting ⫻ Time), suggest there is no evidence for a moderating effect of time; hence the association between the predictor and behavior outcome (e.g., hostile parenting and internalizing-only) is consistent across ages 2 1/2 and 5. Higher levels of maternal anxious/depressive symptoms,

2

.15ⴱⴱ .09

.23

ⴱⴱ

⫺.25ⴱⴱ

4

5

6

1.00 .09

.27ⴱⴱ

3

⫺.03

1.00 .10ⴱ

1.00

.05

ⴱ

.12

.28ⴱⴱ

⫺.14ⴱ

⫺.11ⴱ

⫺.21ⴱⴱ

1.00 ⫺.24ⴱⴱ

1.00

greater family conflict, and younger maternal age increased the risk that children would develop co-occurring problems compared with no problems at ages 2 1/2 and 5 (these predictor by time interactions were all nonsignificant). Finally, there was a significant SES by time interaction differentiating the externalizing-only group from the no problems group (and the internalizing-only group). Further examination of these interactions suggests that an association between higher SES and externalizing-only problems emerged over time. Infants exposed to higher levels of family conflict, infants of mothers with elevated anxious/depressive symptoms, and infants of younger mothers were at greater risk of developing co-occurring problems compared to internalizing-only problems, and the lack of any significant Predictor ⫻ Time interaction terms suggests that these effects were consistent across time. Higher levels of environmental risks, however, did not differentiate infants who developed co-occurring problems from those who developed externalizing-only problems.

Table 2 Means (and Standard Deviations) of Infant Risk Factors by Behavior Group Classification at Age 2 1/2 and Age 5 Infant risk factors Age 2 1/2 Infant anger/frustration Infant distress to novelty Hostile parenting Maternal anxious/depressive symptoms Family conflict SES Age 5 Infant anger/frustration Infant distress to novelty Hostile parenting Maternal anxious/depressive symptoms Family conflict SES

INT

EXT

CO

NONE

6.38 (2.54) 4.86 (8.46) yes: 37.04%

7.08 (3.27) 10.88 (12.11) yes: 24.14%

7.61 (3.29) 5.03 (7.94) yes: 31.11%

5.82 (3.07) 5.58 (9.65) yes: 17.54%

9.85 (5.25) 2.41 (1.80) ⫺.17 (1.24)

10.90 (5.38) 3.36 (2.50) ⫺.59 (1.01)

7.32 (3.27) 3.38 (5.74) yes: 30.30%

6.25 (2.86) 8.71 (12.88) yes: 15.63%

13.09 (5.36) 3.24 (2.39) ⫺.56 (1.35)

9.56 (5.00) 3.74 (2.35) .25 (1.46)

13.82 (7.55) 3.86 (2.42) ⫺.27 (1.13) 8.18 (3.25) 8.34 (13.08) yes: 20.00% 13.86 (7.81) 4.26 (2.28) ⫺.28 (1.22)

8.77 (5.52) 2.30 (1.97) 0.03 (1.52) 5.93 (2.98) 5.01 (8.84) yes: 20.59% 8.27 (5.45) 2.37 (1.98) .12 (1.50)

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Table 3 Mixed-Effects Multinomial Logistic Regression Analysis Predicting Early Childhood Internalizing-Only, Externalizing-Only, and Co-Occurring Behavior Problems From Family Risk Factors During Infancy (n ⫽ 412)

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Infant variables Hostile Parenting Maternal Anx/Dep Family Conflict Family SES Maternal Age Time (T) Hostile Parenting ⫻ T Maternal Anx/Dep ⫻ T Family Conflict ⫻ T Family SES ⫻ T Maternal Age ⫻ T

INT vs. NO

EXT vs. NO

CO vs. NO

INT vs. CO

EXT vs. CO

EXT vs. INT

OR [95% CI]

OR [95% CI]

OR [95% CI]

OR [95% CI]

OR [95% CI]

OR [95% CI]

1.32 [0.39, 4.43] 1.07 [0.97, 1.17] 1.27† [1.00, 1.63] 0.76 [0.48, 1.19] 0.98 [0.90, 1.07] 1.44 [0.67, 3.09] 0.41 [0.08, 2.09] 0.98 [0.87, 1.10] 1.22 [0.90, 1.66] 1.86ⴱ [1.06, 3.29] 0.99 [0.88, 1.10]

1.83 [0.75, 4.49] 1.13ⴱⴱ [1.05, 1.21] 1.31ⴱⴱ [1.08, 1.58] 1.19 [0.85, 1.66] 0.90ⴱ [0.84, 0.98] 0.99 [0.49, 2.01] 0.34 [0.09, 1.30] 1.02 [0.93, 1.11] 1.08 [0.83, 1.40] 0.99 [0.61, 1.61] 1.01 [0.90, 1.12]

1.49 [0.48, 4.64] 0.91ⴱ [0.83, 1.00] 0.75ⴱ [0.57, 0.98] 0.80 [0.52, 1.23] 1.12ⴱ [1.02, 1.23] 1.44 [0.56, 3.67] 1.34 [0.26, 6.93] 1.08 [0.96, 1.21] 1.02 [0.72, 1.45] 0.85 [0.46, 1.55] 0.97 [0.85, 1.10]

0.72 [0.22, 2.35] 0.94 [0.87, 1.03] 0.97 [0.77, 1.24] 0.64† [0.40, 1.02] 1.08 [0.98, 1.19] 1.45 [0.58, 3.64] 1.20 [0.20, 7.12] 0.96 [0.85, 1.09] 1.13 [0.81, 1.58] 1.88† [0.98, 3.61] 0.98 [0.86, 1.12]

0.48 [0.12, 1.94] 1.04 [0.93, 1.16] 1.30† [0.95, 1.77] 0.88 [0.47, 1.35] 0.96 [0.87, 1.07] 1.01 [0.38, 2.69] 0.90 [0.13, 5.97] 0.89 [0.77, 1.03] 1.11 [0.75, 1.64] 2.22ⴱ [1.12, 4.41] 1.01 [0.89, 1.16]

ⴱⴱ

2.72 [1.12, 6.61] 1.03 [0.95, 1.11] 0.98 [0.78, 1.23] 0.95 [0.69, 1.30] 1.02 [0.95, 1.08] 1.43 [0.70, 2.89] 0.45 [0.13, 1.58] 1.09† [0.99, 1.21] 1.10 [0.82, 1.47] 0.84 [0.54, 1.32] 0.97 [0.89, 1.07]

Note. INT ⫽ internalizing-only; EXT ⫽ externalizing-only; CO ⫽ co-occurring; NO ⫽ no behavior problems. † p ⬍ .10. ⴱ p ⬍ .05. ⴱⴱ p ⬍ .01.

Hypothesis 2. Contrary to our hypothesis, infants who showed greater distress to novelty were more likely to be classified as having externalizing-only problems compared with no behavior problems, internalizing-only, and co-occurring problems at both ages (see Table 4). Infants high in anger/frustration were at greater risk of developing co-occurring problems compared to no problems at both ages. Neither component of NE differentiated children with internalizing-only problems from children with no behavior problems. Hypothesis 3. Results of the third model revealed that the Infant Anger ⫻ Hostile Parenting interaction and the Anger ⫻ Hostile Parenting ⫻ Time interaction differentiated the cooccurring group from the no problems group (see Table 5). In order to interpret and display these interactions, estimated population average probabilities associated with combinations of low and high infant anger (⫹/⫺ 1 SD) and hostile versus nonhostile parenting were calculated at each age holding all other predictors at their means. Graphs of these predicted probabilities can be found in Figure 1A and B. The effect of hostile parenting depended on infant temperament: infants high in anger who experienced hostile parenting were at increased risk of developing co-occurring problems compared with no behavior problems. However, the three-way interaction suggests that this effect was significantly weakened by age 5.

The interaction between infant anger and hostile parenting also differentiated the co-occurring group from the internalizing-only group. Infants who experienced hostile parenting but were rated low in anger were at increased risk of developing internalizingonly problems compared with co-occurring problems (see Figure 1B and C). The marginally significant Anger ⫻ Hostility ⫻ Time interaction term suggests that this finding may also fade by age 5.

Discussion The current study examined whether differentiating risk factors for early childhood “pure” and co-occurring behavior problems can be identified in the first year of life. We found evidence for unique influences of multiple environmental risks during infancy on early childhood co-occurring problems. Hostile parenting increased the risk that infants would develop internalizing-only problems compared to no problems, and infant distress to novelty differentiated young children with externalizing-only problems. There was little evidence that negative emotionality (distress to novelty or anger/frustration) increased infant vulnerability to environmental stressors with one exception: Higher levels of infant anger in combination with hostile parenting were associated with later co-occurring problems.

Table 4 Mixed-Effects Multinomial Logistic Regression Analysis Predicting Early Childhood Internalizing-Only, Externalizing-Only, and Co-Occurring Behavior Problems From Infant Anger/Frustration and Infant Distress to Novelty (n ⫽ 412) Infant variables

INT vs. NO OR [95% CI]

EXT vs. NO OR [95% CI]

CO vs. NO OR [95% CI]

INT vs. CO OR [95% CI]

EXT vs. CO OR [95% CI]

EXT vs. INT OR [95% CI]

Infant Anger/Frustration Infant Distress to Novelty Time (T) Infant Anger ⫻ T Infant Distress to Novelty ⫻ T

1.07 [0.94, 1.23] 1.01 [0.71, 1.45] 1.24 [0.71, 2.16] 1.10 [0.92, 1.32] 0.96 [0.60, 1.56]

1.17† [0.99, 1.38] 1.81ⴱⴱ [1.19, 2.76] 1.49 [0.77, 2.89] 0.91 [0.74, 1.12] 0.72 [0.43, 1.21]

1.27ⴱⴱ [1.10, 1.46] 1.08 [0.76, 1.53] 0.75 [0.41, 1.36] 1.04 [0.87, 1.26] 1.07 [0.67, 1.71]

0.85† [0.71, 1.00] 0.94 [0.60, 1.48] 1.66 [0.78, 3.52] 1.05 [0.83, 1.33] 0.90 [0.49, 1.64]

0.92 [0.78, 1.08] 1.68ⴱ [1.11, 2.54] 1.99† [0.93, 4.25] 0.87 [0.69, 1.10] 0.67 [0.38, 1.19]

1.09 [0.90, 1.33] 1.79ⴱ [1.08, 2.97] 1.20 [0.54, 2.69] 0.83 [0.64, 1.07] 0.75 [0.39, 1.43]

Note. INT ⫽ internalizing-only; EXT ⫽ externalizing-only; CO ⫽ co-occurring; NO ⫽ no behavior problems. † p ⬍ .10. ⴱ p ⬍ .05. ⴱⴱ p ⬍ .01.

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Table 5 Mixed-Effects Multinomial Logistic Regression Analysis Predicting Early Childhood Internalizing-Only, Externalizing-Only, and Co-Occurring Behavior Problems From Temperament and Family Risk Factors During Infancy (n ⫽ 412)

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Infant variables

INT vs. NO

EXT vs. NO

CO vs. NO

INT vs. CO

EXT vs. CO

EXT vs. INT

OR [95% CI]

OR [95% CI]

OR [95% CI]

OR [95% CI]

OR [95% CI]

OR [95% CI]

Infant Anger/Frustration 1.04 [0.88, 1.24] Infant Distress to Novelty 0.99 [0.69, 1.42] Hostile Parenting 2.76ⴱ [1.14, 6.69] Maternal Anx/Dep 1.02 [0.95, 1.11] Family Conflict 0.97 [0.78, 1.22] Family SES 0.96 [0.70, 1.32] Maternal Age 1.02 [0.95, 1.09] Infant Anger ⫻ Hostility 1.05 [0.77, 1.43] Time (T) 1.37 [0.70, 2.82] Infant Anger ⫻ T 1.07 [0.84, 1.36] Infant Distress to Novelty ⫻ T 0.99 [0.61, 1.62] Hostile Parenting ⫻ T 0.49 [0.14, 1.75] Maternal Anx/Dep ⫻ T 1.09† [0.99, 1.21] Family Conflict ⫻ T 1.10 [0.82, 1.48] Family SES ⫻ T 0.86 [0.54, 1.36] Maternal Age ⫻ T 0.97 [0.89, 1.07] Infant Anger ⫻ Hostility ⫻ T 0.84 [0.56, 1.28]

0.99 [0.81, 1.21] 1.89ⴱⴱ [1.21, 2.96] 0.95 [0.26, 3.47] 1.08 [0.98, 1.18] 1.22 [0.96, 1.55] 0.85 [0.53, 1.35] 0.97 [0.89, 1.06] 1.32 [0.84, 2.08] 1.61 [0.73, 3.53] 0.99 [0.77, 1.27] 0.76 [0.43, 1.34] 0.43 [0.07, 1.68] 0.97 [0.86, 1.10] 1.23 [0.90, 1.68] 1.74† [0.97, 3.14] 0.99 [0.89, 1.11] 0.88 [0.49, 1.61]

0.99 [0.85, 1.16] 1.05 [0.84, 1.31] 1.21 [0.85, 1.74] 0.82 [0.37, 1.99] 0.91 [0.30, 2.76] 3.03 [0.81, 11.36] 1.13ⴱⴱ [1.05, 1.22] 0.90ⴱ [0.82, 0.99] 1.29ⴱⴱ [1.06, 1.56] 0.76ⴱ [0.57, 0.99] 1.33 [0.93, 1.89] 0.72 [0.46, 1.13] 0.89ⴱⴱ [0.82, 0.96] 1.14ⴱⴱ [1.04, 1.26] 1.72ⴱⴱ [1.17, 2.54] 0.61ⴱ [0.39, 0.95] 0.86 [0.40, 1.81] 1.61 [0.60, 4.28] 1.24† [0.98, 1.56] 0.87 [0.64, 1.18] 1.04 [0.63, 1.71] 0.96 [0.51, 1.80] 0.75 [0.16, 3.67] 0.65 [0.10, 4.19] 1.01 [0.91, 1.11] 1.08 [0.96, 1.22] 1.29 [1.06, 1.56] 1.04 [0.73, 1.49] 1.00 [0.60, 1.66] 0.86 [0.46, 1.61] 1.02 [0.91, 1.15] 0.95 [0.83, 1.09] 0.51ⴱⴱ [0.30, 0.85] 1.66† [0.93, 2.99]

1.00 [0.81, 1.23] 0.95 [0.74, 1.22] 1.56† [0.98, 2.48] 1.90ⴱ [1.11, 3.26] 1.05 [0.26, 4.22] 0.34 [0.08, 1.50] 0.95 [0.87, 1.04] 1.05 [0.94, 1.17] 0.95 [0.74, 1.21] 1.25 [0.92, 1.71] 0.64† [0.39, 1.05] 0.88 [0.51, 1.51] 1.09† [0.99, 1.20] 0.95 [0.86, 1.06] 0.77 [0.49, 1.21] 1.26 [0.76, 2.08] 1.89 [0.71, 4.99] 1.17 [0.43, 3.21] 0.80 [0.59, 1.08] 0.92 [0.67, 1.28] 0.73 [0.39, 1.39] 0.77 [0.38, 1.54] 0.58 [0.07, 4.56] 0.89 [0.11, 6.89] 0.96 [0.85, 1.10] 0.89 [0.77, 1.03] 1.16 [0.83, 1.64] 1.12 [0.75, 1.66] 1.73 [0.87, 3.44] 2.02ⴱ [1.00, 4.11] 0.97 [0.85, 1.12] 1.02 [0.89, 1.17] 1.74† [0.92, 3.30] 1.05 [0.54, 2.05]

Note. INT ⫽ internalizing-only; EXT ⫽ externalizing-only; CO ⫽ co-occurring; NO ⫽ no behavior problems. † p ⬍ .10. ⴱ p ⬍ .05. ⴱⴱ p ⬍ .01.

The current results show that hostile parenting experienced during the first year of life put young children at increased risk of developing internalizing-only problems compared with no problems, and was also associated with co-occurring problems for infants rated high in anger/frustration. The emotional information generated in the mother-infant relationship can influence the early development of self-awareness and self-evaluation (Bretherton, 1985), and infants who experience hostile parenting may begin to see themselves as unworthy of love and comfort. Young children who are consistently criticized may begin to internalize the parent’s evaluations, feel shameful, and develop depressive symptoms (Alessandri & Lewis, 1996). When hostile parenting was observed, infants in general were at increased risk of developing internalizing-only problems; however, only infants temperamentally inclined to anger were at increased risk of developing co-occurring problems compared to no problems. Also, in the context of hostility, infants low in anger were more likely to develop internalizing-only compared with co-occurring problems. This suggests that outcomes associated with hostility may partially depend on temperament. In the presence of hostile parenting, infants prone to anger and frustration may develop anxieties that are partly expressed through crying and aggression as they become toddlers. The distress that develops for infants less inclined to anger may be manifested through increased anxiety and sadness without the co-occurring externalizing behaviors. Infants of mothers with elevated anxious and depressive symptoms were more likely to develop co-occurring problems compared with internalizing-only or no behavior problems, even when accounting for hostility and family conflict. Maternal depression has been associated with both internalizing and externalizing (Goodman et al., 2011), but few have tested whether it more closely links with “pure” problems or their co-occurrence. Our finding does differ from results of Fanti and Henrich (2010), which

showed that postpartum depression was associated with both “pure” and co-occurring problems during childhood. More research is therefore needed to better understand whether early maternal depression is a general risk factor for internalizing and externalizing, or if it is particularly associated with their codevelopment in young children. Family conflict also increased the risk that infants would develop co-occurring problems compared with no problems or internalizing-only problems. Infants exposed to frequent conflict experience negative emotional arousal and feelings of insecurity, which over time can lead to problems with anxiety and depression (Davies & Cummings, 1994). At very young ages, however, these children may also act out their negative feelings in ways that are modeled at home. They may tantrum and become aggressive in times of stress because of how they witness family members expressing emotions. In school-age children, the association between marital conflict and child internalizing, but not externalizing, may be partly mediated through child self-blame (McDonald & Grych, 2006). Although infants can perceive threat during conflict, they lack the cognitive capacity to make self-blaming attributions (McDonald & Grych, 2006), which may also explain why conflict was not associated with “pure” internalizing in this study. We hypothesized that infant anger/frustration would be most closely associated with externalizing problems, while infant distress to novelty would predict internalizing problems, especially in the context of environmental risk. However, infant anger only predicted co-occurring problems, particularly in the presence of hostile parenting, and distress to novelty only predicted externalizing-only problems. The first finding is somewhat consistent with results of Keiley, Lofthouse, Bates, Dodge, and Pettit (2003) who showed that difficult temperament in childhood was associated with co-occurring but not “pure” components of behavior problems. It may be that other aspects of infant temperament,

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INFANT RISKS FOR CO-OCCURRING PROBLEMS

Figure 1. Population average predicted probabilities for no problem behaviors (A), co-occurring problems (B), and internalizing-only problems (C) associated with combinations of hostile/nonhostile parenting and high/ low (⫹/⫺ 1 SD) infant anger/frustration.

such as low positive emotionality or regulatory capacity, are more closely linked to internalizing-only problems. Unlike in previous studies (e.g., Kagan & Snidman, 2004), infant distress to novelty was a specific risk factor for externalizing-only rather than internalizing problems. One interpretation is that infants who cried during the toy task were expressing distress over being confined in a seat or being separated from attachment figures rather than a fearful response to the novel toys. The average age of the infants was 7 months, whereas infants

497

studied by Kagan and colleagues were 4 months old. By 7 months, crying during this task may have signaled anger, frustration, or emerging temperamental resistance to control, which has previously predicted pure externalizing problems (Keiley et al., 2003). Another interpretation offered by Lahey et al. (2008), in finding that infant fearfulness predicted childhood conduct problems, is that fear during infancy reflects general irritability rather than social fear and inhibition that are observed by the preschool years. Looking across early childhood, half of the children who had behavior problems at age 2 1/2 continued to have behavior problems at age 5, which is consistent with one-year persistence rates in young children (Briggs-Gowan et al., 2006). Children with co-occurring problems at 2 1/2 years were most likely to have some type of behavior problem at age 5. With two exceptions, we found little evidence that associations between infant risk factors and behavior problems changed over time, which suggests that experiences during infancy may have lasting effects or that risk factors present in the lives of infants persist over time. The interaction between infant anger and hostile parenting, however, did become significantly weakened between the ages of 2 1/2 and 5, while an association between higher SES and externalizing problems emerged over time. Because both early environmental risks and changes in risks are associated with child behavior problems (Mathiesen, Sanson, Stoolmiller, & Karevold, 2009), it is possible, for example, that hostility and anger measured during early childhood would have been more closely related to age 5 outcomes. More research using longitudinal measures of risks beginning during infancy is needed to distinguish between early, concurrent, or chronic “effects” of these risk factors. The current study had several significant strengths for examining the emergence of early childhood behavior problems. Families were interviewed and observed in their homes, which allowed for measures of parenting behavior in the family’s natural environment. A combination of mother report and observational measures of infant temperament were used to avoid some of the limitations of relying on a single source of information. This study also addressed the problem of missing data, which is almost always an issue in longitudinal studies, through the use of multiple imputation and maximum likelihood estimation. There are also several notable limitations. As is typical in the literature, maternal mental health, family conflict, and child behavior problems were based on mother report, and so correlations between them may be somewhat inflated as a result of reporter bias. Our measure of hostile parenting included only overt displays of hostility; however, more subtle, unobserved forms of hostility may also contribute to behavior problems. Fathers were not interviewed, but paternal psychopathology and hostility may also have implications for child behavior problems. Additionally, “pure” and co-occurring classifications of behavior problems were established using approximate clinical cut-points rather than through diagnostic information. Although we examined temperament by environment interactions, we did not consider possible bidirectional processes. Irritability in infants can evoke intrusive or hostile responses from parents (Rubin & Mills, 1991), which in turn can further exacerbate the already heightened negative emotions in these infants. Additionally, we only tested a vulnerability model of psychopathology because only negative aspects of the family environment were included. According to the theory of differential susceptibil-

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ity, however, children with negative, fearful temperaments may be more susceptible to both the positive and negative effects of the early caregiving environment (Belsky & Pluess, 2009), so future research should explore parenting and environmental factors that may be specifically beneficial for infants high in NE. Because behavior problems can emerge by toddlerhood and risk factors can be identified during infancy, interventions designed to prevent and treat these problems should be implemented at early ages. Co-occurring behavior problems seem to be associated with multiple environmental risks and poor long term outcomes, so these young children may be an especially important group to target for intervention. Interventions that focus on the family and parent– child relationship may be most effective in preventing and treating co-occurring problems. Interventions that target early parenting, and that help parents manage temperamentally difficult infants may be particularly effective in preventing internalizing and externalizing problems.

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Received August 19, 2013 Revision received December 3, 2014 Accepted December 22, 2014 䡲