Psychiatry Research 217 (2014) 72–78

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Sluggish cognitive tempo and peer functioning in school-aged children: A six-month longitudinal study Stephen P. Becker a,b,n a b

Department of Psychology, Miami University, 90 North Patterson Avenue, Oxford, OH 45056, USA Division of Behavioral Medicine and Clinical Psychology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA

art ic l e i nf o

a b s t r a c t

Article history: Received 7 September 2013 Received in revised form 31 January 2014 Accepted 5 February 2014 Available online 14 February 2014

Although research demonstrates sluggish cognitive tempo (SCT) symptoms to be statistically distinct from other child psychopathologies (including attention-deficit/hyperactivity disorder [ADHD], anxiety, depression, and oppositionality) and associated with social impairment, all studies conducted to date have been cross-sectional. Thus, while extant research demonstrates an association between SCT and social functioning, it is entirely unknown whether or not SCT longitudinally predicts increases in social impairment. This study provides an initial examination of the prospective association between SCT symptoms and children's peer functioning. Teachers of 176 children in 1st–6th grades (ages 6–13; 47% boys) provided ratings of children's psychopathology (i.e., SCT, ADHD, anxious/depressive, and oppositional/conduct problems) and peer functioning (i.e., popularity, negative social preference, peer impairment), and peer functioning was assessed again 6 months later. Multilevel modeling analyses indicated that, above and beyond child demographics, other psychopathologies, and baseline peer functioning, SCT symptoms were significantly associated with poorer peer functioning at the 6-month follow-up. In addition, 75% of children with high levels of SCT were rated as functionally impaired in the peer domain, in contrast to only 8% of children with low SCT. Further research is needed with larger samples to examine SCT over a longer developmental period and with other domains of adjustment. & 2014 Elsevier Ireland Ltd. All rights reserved.

Keywords: ADHD Attention deficit disorder Concentration deficit disorder Impairment Peer rejection Sluggish cognitive tempo Social functioning

1. Introduction Sluggish Cognitive Tempo (SCT) is defined by daydreaming, drowsiness, lethargy, mental confusion, and seeming to be in a world of one's own. Although initially identified as a set of symptoms hypothesized to be useful for identifying a distinct set of children with Attention-Deficit/Hyperactivity Disorder (ADHD) Predominately Inattentive Type (ADHD-I) (McBurnett et al., 2001; Carlson and Mann, 2002), recent studies do not convincingly support the hypothesis that the presence of elevated SCT is useful for identifying a subset of children diagnosed with ADHD-I (Marshall et al., 2014; Willcutt et al., 2014). Still, SCT has recently gained attention for its broader relevance for child adjustment (Becker, 2013; Barkley, 2014; Becker et al., 2014b). In support of the increased attention devoted to the SCT construct, multiple studies using a variety of sample types and age ranges have demonstrated SCT to be statistically distinct from DSM-IV ADHD (Willcutt et al., 2012; Barkley, 2013) as well as symptoms of n Correspondence address: Department of Psychology, Miami University, 90 North Patterson Avenue, Oxford, OH 45056, USA. Tel.: þ1 513 803 2066; fax: þ1 513 803 0084. E-mail address: [email protected]

http://dx.doi.org/10.1016/j.psychres.2014.02.007 0165-1781 & 2014 Elsevier Ireland Ltd. All rights reserved.

anxiety and depression (Burns et al., 2013; Becker et al., 2014a; Lee et al., 2014; Willcutt et al., 2014). Further, a growing body of research demonstrates that SCT is not only separable from ADHD and other psychopathologies but also related to a range of psychosocial impairments (see Barkley, 2014; Becker, 2013, for reviews). Given these findings, it has been suggested that SCT may be itself a distinct psychiatric disorder (Concentration Deficit Disorder; Barkley, 2014), although much more research is needed before determining precisely what role SCT should ultimately have in psychiatry, psychology, and developmental psychopathology. One of the most consistent findings to date is that of an association between SCT and social impairment. Multiple studies have documented a significant relation between SCT symptoms and general social problems (Bauermeister et al., 2012; Becker and Langberg, 2013; Burns et al., 2013; Becker et al., 2014a; Lee et al., 2014; McBurnett et al., 2014; Willcutt et al., 2014). SCT symptoms have also been shown to be significantly associated with sensitivity to punishment broadly and shyness/fear specifically (Becker et al., 2013a). Other studies have shown that among youth with ADHD-I, those with high levels of SCT are more socially withdrawn (and less aggressive) than those without high SCT (Carlson and Mann, 2002; Marshall et al., 2014). In line with these findings, Willcutt and colleagues (2014) found SCT symptoms to be

S.P. Becker / Psychiatry Research 217 (2014) 72–78

uniquely associated with social isolation after controlling for inattentive and hyperactive-impulsive symptoms. Finally, SCT symptoms were associated with a poorer perception of subtle social cues and less memory for a laboratory-based chat room conversation (Mikami et al., 2007). Although these studies suggest that SCT is an important construct for understanding youth's social adjustment, a significant limitation of SCT-related research conducted to date is that all studies have used a cross-sectional design. Thus, while extant research demonstrates an association between SCT and social functioning, it is entirely unknown whether or not SCT longitudinally predicts increases in social impairment. Therefore, the purpose of the present study was to provide an initial examination of the longitudinal association between SCT symptoms and children's peer functioning. Since the use of clinic-based samples of children diagnosed with ADHD make it “difficult to identify distinctive features that may be associated with SCT” (Barkley, 2013, p. 162), a non-referred school-based sample of children was used in the present study. Specifically, the teachers of children in first through sixth grades participated in a 6-month longitudinal study examining SCT in relation to subsequent peer functioning. In addition to being the first study to examine SCT as a longitudinal predictor of children's adjustment, multiple domains of peer functioning were examined (i.e., popularity, negative social preference, impairment in the peer domain). Since SCT is linked to social withdrawal, mental confusion, and slow processing, it was hypothesized that SCT symptoms would predict poorer peer functioning over a 6-month period, even after controlling for baseline peer functioning and other psychopathologies (i.e., ADHD inattentive, ADHD hyperactive-impulsive, anxious/depressive, and conduct/oppositional symptoms). Additional analyses were conducted that compared children with high levels of SCT to children with low levels of SCT, with the expectation that children with elevated SCT would have higher levels of other psychopathology symptoms and functional impairment in the peer domain than children without elevated SCT.

2. Methods 2.1. Participants The current study included teacher ratings of 176 students attending an elementary school in the Midwestern United States. Students included in this study were in first through sixth grades (ages 6–13 at the fall time point, M¼ 9.17, S. D. ¼ 1.82). The sample was approximately equally split between boys (n¼ 82; 47%) and girls (n ¼94; 53%). According to official school records, and consistent with demographics of the surrounding community (95% White in the 2010 United States Census), the majority of participants in this study were White (n¼ 164; 93%) with remaining participants African American (n¼ 9; 5%) or Asian (n¼ 3; 2%). According to the 2010 Census, 28.4% of the city population was below the federal poverty level (median household income¼ $30,299). Fifty-two percent (n¼ 92) of the students included in this study received free or reduced lunch, which was used in the present study as a marker of socioeconomic status. To further describe the sample, the county in which the school resides is classified by the 2013 Rural-Urban Continuum Codes as nonmetropolitan (specifically, Code 6: Urban population of 2500 to 19,999, adjacent to a metro area). 2.2. Procedures All study procedures were approved by the university Institutional Review Board (IRB). Approximately one month into the school year, the principal investigator described the study to teachers of grades one through six. Teachers were told that participation in the study included completing measures for participating students at both the fall and spring time points (i.e., T1 and T2) but that they could withdraw their consent at any time during the duration of the study. All eligible teachers (i.e., mainstream classroom teachers of students in grades one through six) provided signed informed consent to participate in the study at both time points (N ¼12; i.e., two teachers for each of the first through sixth grades). After the teachers provided informed consent, the study was described by research staff to the students in each teacher's classroom. Students were explicitly

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told that whether or not they participated in the study would have no effect on their grades or overall school functioning. After answering any student questions, students were given informed consent forms for them to take home to their parents. Students were told that teachers would reward students for returning the informed consent forms by giving them a “blue ticket” (a reward system implemented across all grades at the school), but that these tickets were given simply for bringing the form back regardless of whether the form was signed giving permission or declining permission for the student to participate in the study. The parent consent form informed parents that student participation in the study was fully optional, that providing consent was allowing for the student's teacher to complete forms regarding their child at the fall and spring time-points (i.e., T1 and T2), and that parents could revoke consent for participation in the study at any time. Parents were also given the e-mail address and phone number of the research team in the event that they had any questions or concerns. Students had 2 weeks to return the consent forms to the school. After 1 week, teachers were prompted by research staff to give students who had not yet turned in the parent informed consent form a new copy to take home. Of the 280 total students in grades one through six at T1, 218 (78%) returned their consent forms. Of those, 189 (87% of those who returned their consent forms) provided consent for their child to participate in the study, and 176 (93% of the T1 sample) were still attending the school at T2 and were included in the current study analyses. Teachers were given a packet with the study measures to complete in reference to each participating student in October (T1) and 6 months later in April (T2). Teachers were asked to complete the packets within 2 weeks and were compensated $5 and $7 for each packet they completed at the baseline and 6-month follow-up time points, respectively.

2.3. Measures 2.3.1. Child demographic variables Official school records were used to gather demographic information for each participating student. Specifically, age, sex, race, and free or reduced lunch status data were collected. Age, sex, and free or reduced lunch status variables were used as covariates in the study analyses. Given the very few non-White students in the school, student race information was collected to describe the sample but was not used as a covariate.

2.3.2. Child psychopathology At T1, teachers completed the 35-item Vanderbilt ADHD Diagnostic Teacher Rating Scale (VADTRS; Wolraich et al., 1998, 2013), which is a well-validated teacher-report measure of child psychopathology. The VADTRS includes 18 items that correspond to the DSM-IV symptoms of ADHD (nine items assessing inattention and nine items assessing hyperactivity-impulsivity) in addition to 10 items assessing conduct/oppositional problems and seven items assessing anxiety/ depression problems. Each item is rated on a four-point scale (0 ¼never, 1¼ occasionally, 2¼ often, 3¼very often). Construct and convergent validity of the VADTRS have been established and the VADTRS subscales demonstrate acceptable internal consistency and test–retest reliability (Wolraich et al., 1998, 2013). In the present study, internal consistencies of the mean scale scores were adequate: ADHD Inattention α ¼0.95, ADHD Hyperactivity-Impulsivity α ¼ 0.89, Conduct/ Oppositional α ¼ 0.89, Anxiety/Depression α ¼ 0.87. At T1, teachers also completed the SCT Scale developed by Penny et al. (2009). Previous studies of SCT had primarily relied on brief measures of SCT that lacked psychometric validation. In response to the need for an empirically supported measure of SCT in children, Penny et al. (2009) first conducted a review of the literature in order to identify an initial pool of SCT items and then used a group of experts in the field of SCT to evaluate the content validity of these items. Results from this process led to the identification of a 14-item SCT scale which was then validated in a sample of 335 elementary school-aged children. Similar to the VADTRS, each item on the SCT scale is rated on a four-point scale (0 ¼not at all, 1¼ just a little, 2¼ pretty much, 3¼ very much). Penny et al. (2009) provided initial support for the reliability (i.e., internal consistency, interrater reliability, and test– retest reliability) and external validity (i.e., convergent and discriminant validity) of the 14-item SCT scale. For example, although Penny et al. (2009) were unable to examine the test–retest reliability for the teacher-report version of their measure, they reported the test–retest reliability for the 14-item parent-report version to be 0.87 over a period of approximately 12 weeks (Penny et al., 2009). In their study, Penny et al. (2009) also conducted two sets of principal components analysis (PCA) in order to examine the 14 SCT items in isolation as well as to examine the SCT items in tandem with DSM-IV ADHD items. The authors conducted separate analyses for parent and teacher ratings, but since only teacher ratings of SCT were collected in the present study, the Penny et al. (2009) results specific to the teacherreport measure are described here. Specifically, Penny et al. (2009) identified a twofactor structure of SCT (i.e., Sleepy/Daydreamy and Slow factors) when examining the teacher-reported SCT items in a PCA, with three of the items cross-loading on both SCT factors. However, a subsequent PCA that included the 14 SCT items in addition to the 18 DSM-IV ADHD items found that the SCT Slow items loaded with the ADHD Inattention items. The eight remaining SCT items comprised a factor that was distinct from ADHD Inattention/SCT Slow and ADHD Hyperactivity-Impulsivity.

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S.P. Becker / Psychiatry Research 217 (2014) 72–78

These eight SCT items are: appears to be sluggish; seems drowsy; daydreamy; appears tired, lethargic; seems to be in a world of his or her own; has a yawning, stretching, or sleepy-eyed appearance; is underactive, slow moving, or lacks energy; and gets lost in his or her own thoughts. Given the importance of using a measure of the SCT construct that is distinct from DSM-IV ADHD Inattention, a mean scale score consisting of these eight SCT items were used in the present study as the measure of SCT (α ¼ 0.92).

from children with low levels of SCT on demographics, other psychopathology symptoms, and, most germane to the purpose of this study, functional impairment in the peer domain.

2.3.3. Peer functioning At T1 and T2, teachers completed three measures of peer functioning:

3.1. Correlation analyses

2.3.3.1. Popularity. The popularity subscale from the Interpersonal Competence Scale (ICS; Cairns et al., 1995) was used to measure each student's popularity within the peer group. The popularity subscale of the ICS consists of three items, and each is rated using a seven-point scale whereby each end is represented by polar opposites (i.e., no friends/lots of friends, not popular with girls/very popular with girls, not popular with boys/very popular with boys). Teachers check one of the seven boxes along the continuum and items are coded such that higher scores indicate higher levels of popularity. The ICS popularity subscale demonstrates acceptable reliability and validity (median internal consistency across longitudinal cohorts ¼0.81; Cairns et al., 1985, 1995), including being significantly associated with a child interviewbased measure of social structure (Cairns et al., 1985). In addition, the ICS popularity items consistently loaded together in separate 9- and 6-year cohort studies and for both boys and girls (Cairns et al., 1995). Cairns et al. (1995) also reported a median (across grade and sex) 3-week test–retest reliability of 0.82. In the present study T1 α ¼0.91 and T2 α ¼ 0.94. 2.3.3.2. Negative social preference. Teachers rated children's social preference using the Dishion Social Acceptance Scale (DSAS; Dishion, 1990) which is a teachercompleted measure of child social status. Using a five-point scale (1¼ almost none, less than 25%; 5 ¼nearly all, over 75%), teachers rate the proportion of classmates who “dislike/reject” and “like/accept” the target child. Consistent with previous research (e.g., Lahey et al., 2004; Lee and Hinshaw, 2006; Becker et al., 2013b), these two items were then used to create a negative social preference score that simultaneously considers both positive and negative dimensions of peer status. Specifically, a negative social preference score is created by subtracting the reject/ dislike rating from the accept/like rating and then reverse-scoring the scale so that higher scores indicate higher levels of negative social preference. This measure of negative social preference has been well-validated (Dishion, 1990) and is sensitive to differences between children with and without ADHD over a 3-year period (Lahey et al., 2004). In addition, previous research indicates that this measure of negative social preference is significantly associated with peer sociometric nominations (Lee and Hinshaw, 2006) and teacher-report of child depressive symptoms and externalizing problems (Becker et al., 2013b). 2.3.3.3. Impairment in peer functioning. In addition to the psychopathology symptoms described above, the VADTRS (Wolraich et al., 1998, 2013) also includes performance items assessing functional impairment. These items are rated on a fivepoint scale with higher scores indicative of greater impairment (1 ¼excellent, 2¼ above average, 3¼ average, 4¼ somewhat of a problem, 5¼ problematic). A rating of “4” or “5” indicates the presence of functional impairment. The item assessing performance in “relationships with peers” was included in this study as a measure of impairment in peer functioning. Research demonstrates that ADHD, oppositional/conduct, and internalizing symptoms are each significantly associated with higher ratings on this peer impairment item (Garner et al., 2013). In addition, children with ADHD are rated on the parent-report version of this item as more impaired in their peer functioning than children without ADHD (Becker et al., 2012). 2.4. Statistical analyses First, correlation analyses were conducted to examine whether child demographic characteristics and psychopathology during the fall semester (T1) were bivariately associated with peer functioning 6 months later (T2). Next, primary study analyses were conducted to examine whether T1 SCT symptoms predicted T2 peer functioning above and beyond T1 peer functioning, child demographics, and other psychopathology symptoms. Given that students were nested within 12 different classrooms (with each teacher rating between nine and 23 students; Median¼ 14 students), multilevel modeling using the SPSS Mixed Model procedure was used for the primary analyses. Specifically, the model was set up such that the predictors at Level 1 were child demographics (i.e., age, sex, free/reduced lunch status), child psychopathology dimensions (i.e., SCT, inattention, hyperactivityimpulsivity, anxiety/depression, conduct/oppositional problems), and baseline peer functioning. Although no predictors at the classroom level (Level 2) were included in the models, this nested level was included in the model to control for shared variance and the possibility that teacher ratings of children within the same classroom may be nonindependent from each other. Finally, analyses were conducted to examine the degree to which children with high levels of SCT differed

3. Results

First, correlations among study variables at T1 were examined. Compared to their peers, children receiving free or reduced lunch had higher levels of both SCT symptoms (r ¼0.20, p ¼0.008) and ADHD inattentive symptoms (r ¼0.16, p ¼0.03). Boys and girls did not differ on teacher-reported internalizing symptoms, but boys were rated by teachers as displaying more SCT, inattentive, hyperactive-impulsive, and conduct/oppositional symptoms than girls (rs ¼  0.17 to  0.23, all ps o0.05). Child age was positively associated with inattentive, conduct/oppositional, and internalizing symptoms (rs ¼ 0.15–0.21, all ps o0.05), but age was not correlated with SCT or hyperactive-impulsive symptoms. Consistent with previous research, SCT symptoms were more strongly associated with inattentive and internalizing symptoms (rs ¼ 0.77 and 0.43, respectively) than with hyperactive-impulsive and conduct/oppositional symptoms (rs ¼0.28 and 0.24, respectively). Table 1 displays the bivariate correlations between child demographics and T1 peer functioning/psychopathology variables and T2 peer functioning. Child age was positively correlated with T2 negative social preference, and girls were less likely than boys to be rated as impaired in the peer domain. Children receiving free or reduced lunch had significantly poorer peer functioning than other children (ps o0.05 across all three peer domains). As expected, T1 peer functioning was strongly associated with T2 peer functioning (all ps o 0.001), indicating that peer functioning was relatively stable across the school year. All correlations were in the expected direction, with T1 popularity negatively correlated with T2 negative social preference and peer impairment (rs ¼  0.69 and  0.68, respectively) and T1 negative social preference and peer impairment negatively correlated with T2 popularity (rs ¼  0.63 and  0.68, respectively). In addition, all of the T1 psychopathology dimensions were significantly correlated with T2 peer functioning (all ps o 0.001), with the strongest correlations found for ADHD inattentive and SCT symptoms in relation to peer functioning (see Table 1). 3.2. Multilevel modeling analyses Multilevel modeling analyses were conducted to examine whether SCT symptoms predicted children's peer functioning six months later above and beyond child demographics, other psychopathologies, and baseline peer functioning. Results are summarized in Table 2. As expected, T1 peer functioning was a very strong predictor of T2 peer functioning across all three peer domains (all ps o 0.001), making the inclusion of T1 peer functioning in the models a rather stringent test since it required SCT to account for additional variance in predicting T2 peer functioning after controlling for the expected temporal stability in each peer domain. In the model predicting popularity (see Table 2), after controlling for T1 popularity, demographics, and other psychopathology dimensions, T1 oppositional/conduct problems were significantly positively associated with popularity (p ¼0.049) whereas T1 ADHD hyperactive-impulsive symptoms were significantly negatively associated with popularity (p ¼0.009). Also, and as hypothesized, SCT symptoms were significantly negatively associated with popularity (p ¼0.02) above and beyond the other predictor variables in the model.

S.P. Becker / Psychiatry Research 217 (2014) 72–78

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Table 1 Correlations of child demographics, T1 peer functioning, and T1 psychopathology symptoms with T2 peer functioning. Variable

M 7 S.D.

T2 popularity (M ¼4.977 1.47)

T2 negative social preference (M¼  2.29 7 1.82)

T2 peer impairment (M ¼ 2.79 7 0.98)

Child demographics T1 age Sex Free/reduced lunch status

9.177 1.82 – –

0.01 0.08  0.20nn

0.21nn  0.09 0.18n

0.02  0.16n 0.16n

T1 peer functioning Popularity Negative social preference Peer impairment

5.03 7 1.47  2.38 7 1.79 2.69 7 0.98

0.73nnn  0.63nnn  0.68nnn

 0.69nnn 0.73nnn 0.66nnn

 0.68nnn 0.65nnn 0.73nnn

Child psychopathology Anxiety/depression Conduct/oppositional ADHD hyperactive-impulsive ADHD inattention SCT

0.277 0.43 0.147 0.31 0.36 7 0.51 0.63 7 0.69 0.357 0.52

 0.37nnn  0.25nnn  0.28nnn  0.50nnn  0.51nnn

0.44nnn 0.46nnn 0.40nnn 0.50nnn 0.49nnn

0.41nnn 0.36nnn 0.37nnn 0.50nnn 0.49nnn

Note: N ¼176. ADHD-HI¼ attention-deficit/hyperactivity disorder. SCT ¼ sluggish cognitive tempo. T1¼ time point 1 (Fall). T2 ¼ time point 2 (Spring). For sex: 0 ¼male, 1¼ female. For free/reduced lunch status: 0¼ student does not receive a free or reduced lunch, 1¼ student receives free or reduced lunch. n

po 0.05 p o0.01 p o 0.001

nn

nnn

Table 2 Multilevel models of T1 Sluggish Cognitive Tempo (SCT) symptoms predicting T2 peer functioning. Fixed effects

Intercept Free/reduced lunch Sex T1 age T1 peer functioninga T1 anxiety/depression T1 conduct/oppositional T1 ADHD inattention T1 ADHD hyp-impulsivity T1 SCT

T2 popularity

β00 β01 β02 β03 β04 β05 β06 β07 β08 β09

T2 negative social preference

T2 peer impairment

B

SE

t

B

SE

t

B

SE

t

1.27  0.05  0.20 0.03 0.75  0.19 0.50 0.09  0.48  0.48

0.69 0.12 0.12 0.07 0.05 0.19 0.25 0.19 0.18 0.21

1.85  0.44  1.59 0.43 14.13nnn  1.01 1.98n 0.48  2.61nn  2.35n

 2.35 0.19 0.39 0.11 0.65  0.01  0.15  0.28 0.49 0.91

0.69 0.18 0.19 0.07 0.08 0.29 0.42 0.28 0.27 0.31

 3.42nn 1.06 2.06n 1.55 8.41nnn  0.03  0.37  0.98 1.77 2.94nn

1.11 0.03  0.02  0.01 0.58 0.15  0.05  0.14 0.27 0.43

0.37 0.10 0.11 0.04 0.07 0.16 0.22 0.16 0.15 0.17

3.00nn 0.27  0.17  0.25 8.84nnn 0.95  0.21  0.88 1.74 2.52n

Note: N ¼ 176. ADHD ¼attention-deficit/hyperactivity disorder. SCT ¼ sluggish cognitive tempo. T1¼ time point 1 (Fall). T2 ¼time point 2 (Spring). For sex: 0¼ male, 1¼ female. For free/reduced lunch: 0¼ student does not receive a free or reduced lunch, 1 ¼ student receives free or reduced lunch. a

T1 peer functioning refers to the baseline score on the corresponding T2 peer functioning outcome domain. po 0.05 p o0.01 nnn p o 0.001 n

nn

In addition, SCT symptoms were the only psychopathology to be significantly associated with negative social preference (p ¼0.004), with higher SCT predicting higher negative social preference scores after controlling for baseline negative social preference and other psychopathologies. Likewise, SCT symptoms were the sole psychopathology to be significantly associated with peer impairment (p ¼0.01) after controlling for baseline peer impairment, demographics, and other psychopathologies (see Table 2). 3.3. Comparing children with high or low SCT Next, participants with either high or low levels of SCT were compared across study variables. Students with SCT scores Z1SD above the SCT mean were classified as having high SCT (n ¼24; 13.6%) whereas students with SCT scores at or below the SCT mean were classified as having low SCT (n ¼113; 64.2%). Children with high or low SCT did not differ on age (t¼  0.89, p ¼0.37), but children in the high SCT group were more likely than children in the low SCT group to be male (χ2 (1) ¼11.51, p ¼0.001) and to receive free or reduced lunch (χ2 (1)¼ 5.23, p ¼0.02). Specifically,

males comprised 75% of the high SCT group and 37% of the low SCT group; 71% of the high SCT group received free or reduced lunch in comparison to 45% of the low SCT group. In addition, after applying a Bonferroni correction (0.05/4 ¼0.0125), children with high SCT had higher rates of ADHD inattentive, ADHD hyperactiveimpulsive, anxious/depressive, and oppositional/conduct problems in comparison to children with low SCT (all ps o0.01). After again applying a Bonferroni correction (0.05/6 ¼0.008) and as expected given the multilevel analyses above, children with high SCT also had poorer peer functioning across each of the three peer domains at both T1 and T2 (all ps o0.001). Finally, children with high vs. low SCT were compared on the degree to which they experienced functional impairment in the peer domain as defined by being rated on the VADTRS relationship with peers item as somewhat of a problem (score of “4”) or problematic (score of “5”). As summarized in Table 3 and displayed in Fig. 1, children with high SCT were rated as more frequently impaired in the peer domain than children with low SCT, χ2 (2) ¼ 57.25, p o0.001. That is, 75% (n ¼ 18) of children with high SCT were rated as impaired in the peer domain on at least one time point (and 37.5% were rated as peer impaired at both time points),

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S.P. Becker / Psychiatry Research 217 (2014) 72–78

Table 3 Frequency of functional impairment in the peer domain among children with high or low levels of SCT. Group

Peer impairment at neither T1 nor T2

Low SCT 92% (n¼ 104) (n ¼113) 25% (n¼ 6) High SCT (n ¼24)

Peer impairment at T1 or T2

Peer impairment at T1 and T2

5% (n¼ 6)

3% (n¼ 3)

37.5% (n¼ 9)

37.5% (n¼9)

Note: N ¼ 137. SCT ¼sluggish cognitive tempo. T1 ¼time point 1 (Fall). T2 ¼time point 2 (Spring).

100%

92%

Percent

80% 60% 37.5%

40%

37.5%

25%

20% 5%

3%

0% No Peer Impairment

T1 or T2 Peer Impairment

Low SCT (n = 113)

T1 and T2 Peer Impairment

High SCT (n = 24)

Fig. 1. Percentage of children with Low SCT (n¼ 113) or High SCT (n¼ 24) who were rated by teachers as not impaired or functionally impaired in the peer domain at T1 and/or T2. T1 ¼ time point 1 (Fall). T2¼ time point 2 (Spring).

whereas only 8% (n¼ 9) of children with low SCT were rated as impaired in the peer domain on at least one time point (and only 2.7% were rated as peer impaired at both time points). Conversely, 92% of children with low SCT were not rated at either time point as being impaired in the peer domain, in comparison to 25% of children with high SCT.

4. Discussion To date, all studies examining the external validity of SCT have used a cross-sectional design, making longitudinal studies a clear research priority. This study makes an important contribution to the current literature by using a validated measure of SCT to examine whether SCT prospectively predicted peer functioning over a 6-month period in a sample of 176 school-aged children. Results from the present study indicated that, after controlling for the temporal stability of peer functioning, child demographic characteristics, and symptoms of ADHD, oppositional defiant/ conduct disorder, and anxiety/depression, SCT significantly predicted poorer peer functioning 6 months later, with results consistent across three domains of peer adjustment (i.e., popularity, negative social preference, and impairment in peer relations). In addition, children with high SCT were more likely to be rated as clinically impaired in their peer functioning than children with low SCT, with 75% of children in the high SCT group being rated by teachers at the fall and/or spring time point as experiencing peer impairment (in comparison to 8% of the low SCT group). These results build upon a growing body of cross-sectional studies that have shown SCT to be significantly correlated with social functioning, including general social problems/impairment (Becker and Langberg, 2013; Burns et al., 2013; Lee et al., 2014), withdrawal (Carlson and Mann, 2002; Marshall et al., 2014;

Willcutt et al., 2014), and a poorer perception of social cues (Mikami et al., 2007). Although this pattern of results is generally consistent across studies, exceptions have been reported, particularly when different informants were considered. For example, both Bauermeister et al. (2012) and McBurnett et al. (2014) found SCT symptoms to be associated with teacher-reported social skills but not parent-reported social skills when controlling for ADHD inattentive and hyperactive-impulsive symptoms. In addition, Watabe et al. (2014) found children with high levels of SCT to be rated by teachers as less impaired in their peer relationships in comparison to children with low levels of SCT, although it should be noted that this buffering effect was only found when child age and ADHD symptom severity were covaried; see Watabe et al., 2014, Table 2. The results of the present study clearly align more closely with the results of the Bauermeister and McBurnett studies, but since only teacher-reports of peer functioning were included in the present study it will be important for future research to further investigate how SCT may differentially relate to functioning in the school and home contexts (although it should also be noted that other studies stand in contrast to the results of Bauermeister and McBurnett by finding a relation between SCT and parent-reported social impairment; Becker and Langberg, 2013; Burns et al., 2013). Nonetheless, results from the current study demonstrate that SCT symptoms negatively impact children's peer functioning as rated by teachers across a 6-month period, with results consistent across the peer domains of popularity, negative social preference, and peer impairment. It is compelling that these results were found even after controlling baseline peer functioning (in addition to demographics and other psychopathologies). That is, SCT predicted poorer peer functioning at the 6-month follow-up even when the stability of children's peer adjustment was accounted for, which is a rather stringent test given the relatively short length of time considered in the present study. It is likely that the daydreamy, sluggish, slow, lethargic, and confused behaviors that are characteristic of SCT lead to children isolating themselves from the peer group in tandem with peers increasingly ignoring these children over time. In line with the findings using dimensional SCT symptom scores, grouping analyses based on high or low levels of SCT symptoms provided further evidence for the adverse effects of SCT on children's mental health and peer functioning. Fourteen percent of the current sample had high levels of SCT, and these children had higher rates of ADHD, anxiety/depression, and oppositional/conduct symptoms than children with low levels of SCT. The children with high SCT also had poorer peer functioning at both time points, including being rated as less popular and having higher negative social preference scores and more peer impairment than children with low SCT. Likewise, the vast majority (92%) of children with low levels of SCT were not rated by their teacher as being impaired in the peer domain at either time point. In stark contrast, three-quarters of children with high levels of SCT were rated as impaired in the peer domain on at least one time point (see Fig. 1). Moreover, over a third (38%) of children with high SCT were impaired in the peer domain at both time points whereas only three children (2.7%) with low SCT were peerimpaired at both time points (see Table 3). Additional research is needed to test not only the stability of elevated SCT symptoms over time, but also the degree to which stability of SCT is also associated with ongoing peer impairment. Finally, although not the primary aim of this study, the finding that children with high SCT were more likely than children with low SCT to receive free or reduced lunch warrants some mention. Similarly to results of the present study, Barkley (2013) found that children with SCT alone or SCT with comorbid ADHD had a significantly lower family income than control children and children in either of the SCT groups also had parents with lower

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education levels than children with either ADHD alone or control children. In addition, in the one twin study to date that examined the genetic and environmental contributions to SCT and ADHD, SCT symptoms were somewhat more influenced than either inattention or hyperactivity-impulsivity by non-shared environmental factors (Moruzzi et al., 2014). Very little research has examined the etiology of SCT, and attending to biologicallybased contributions as well as possible environmental factors (e.g., poverty, family conflict, adverse childhood experiences) to the development and maintenance of SCT is clearly an area for increased research attention.

4.1. Study limitations and future directions Although this study offers an important first step towards examining the developmental psychopathology of SCT, more longitudinal research is clearly needed. The results presented in this study are the first to document SCT symptoms in relation to children's later adjustment, but several limitations should be noted. First, only teacher-ratings of peer functioning were collected. Incorporating multiple indicators of peer functioning is a strength of the current study, but it will be important for future studies to incorporate other measures of peer functioning (e.g., parent ratings, sociometric peer nominations), in addition to considering other domains of adjustment. Second, the sample size in this study was relatively small and thus limited the types of research questions that could be examined, but the promising results reported highlight the need for additional studies with larger samples that have the statistical power to test more complex models. Third, since a nonclinical school-based sample was used in this study, the findings regarding children with “high SCT” should be considered preliminary, although it is noteworthy that even children with high SCT in this school-based sample were frequently rated by their teachers as impaired in the peer domain. Finally, this study was limited to a 6-month longitudinal design with only two measurement points, making the examination of SCT across a longer period and with multiple time-points of critical importance for uncovering the longitudinal, moderating, and mediating effects of SCT across development. In sum, this study builds upon previous research that has shown SCT to be distinct from ADHD (and other psychopathologies) and correlated with social functioning by also demonstrating SCT to be predictive of children's later peer functioning. Results from this study point toward the need for additional longitudinal research with larger samples that can examine the predictive validity of SCT in relation to a range of psychosocial domains across development.

Acknowledgment The author thanks the teachers who participated in this study, as well as Aaron Luebbe for his assistance with study design and the undergraduate students who assisted with data collection.

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