Abstract
The past decade has seen renewed interest in the construct of sluggish cognitive tempo (SCT), which is defined with a range of behavioral symptoms such as drowsiness, daydreaming, physical hypoactivity, lethargy, and apathy (e.g., Barkley, 2011; Carlson & Mann, 2002; McBurnett, Pfiffner, & Frick, 2001). There is a growing body of evidence suggesting that a significant minority of children with ADHD–Predominantly Inattentive Type (ADHD-I) are best characterized by the presence of SCT symptoms and relative absence of hyperactive/impulsive symptoms (Carlson & Mann, 2002). It has also been suggested that this compilation of symptoms may represent a disorder distinct from ADHD (Milich, Balentine, & Lynam, 2001), although few empirical studies have directly examined this possibility (e.g., Barkley, 2011). However, as recently noted (Garner, Marceaux, Mrug, Patterson, & Hodgens, 2010; Harrington & Waldman, 2010), little is known about the relation between SCT symptoms and functional impairment in youth with ADHD. Given that social and academic impairment are highly prevalent among youth with ADHD, and that impairment is an integral part of an ADHD diagnosis, these relations warrant further investigation.
Although information on impairment is lacking, there is evidence to support a positive association between SCT and internalizing symptoms. This association has been found in school-based and clinical samples (Carlson & Mann, 2002; Garner et al., 2010; Penny, Waschbusch, Klein, Corkum, & Eskes, 2009; Wåhlstedt & Bohlin, 2010), although exceptions have also been reported (Harrington & Waldman, 2010). Clinic-referred youth with comorbid ADHD and anxiety have higher rates of SCT than youth with ADHD alone (Skirbekk, Hansen, Oerbeck, & Kristensen, 2011). Research with nonreferred children also suggests that a robust relation exists between SCT and internalizing symptoms, even after controlling for symptoms of inattention (Penny et al., 2009).
In contrast to internalizing mental health symptoms, findings regarding SCT and externalizing mental health symptoms are more mixed. Garner et al. (2010) reported a significant positive correlation between SCT and parent-reported aggression (but not rule-breaking behavior) among clinic-referred youth. However, Harrington and Waldman (2010) found that clinic-referred children with ADHD and high levels of SCT did not differ from children with ADHD and low levels of SCT in externalizing symptoms. In contrast, using a school-based sample of children with elevated levels of teacher-reported ADHD-I symptoms, Carlson and Mann (2002) found that children with high levels of SCT had significantly lower rates of externalizing symptoms than did children with low levels of SCT.
Research to date also suggests that SCT may be linked to social functioning. SCT behaviors are significantly correlated with parent- and teacher-reported social problems (Garner et al., 2010). Furthermore, children with ADHD-I symptoms and high levels of SCT have been shown to have greater social problems than children with ADHD-I symptoms and low levels of SCT (Carlson & Mann, 2002). In addition, SCT is associated with missing more social cues and lower rates of hostility in a chat room performance task, even after accounting for the contribution of ADHD diagnostic group status (Mikami, Huang-Pollock, Pfiffner, McBurnett, & Hangai, 2007). However, the studies cited earlier did not control for ADHD severity or the presence of externalizing symptoms that uniquely predict social problems and related problems such as aggression (Becker, Luebbe, Stoppelbein, Greening, & Fite, 2011; Mikami & Lorenzi, 2011). This leaves open the possibility that common co-occurring behaviors such as oppositionality, rather than SCT, are responsible for this relation with social problems.
Few studies have examined the relation between SCT and academic functioning, despite the impact that symptoms such as drowsiness and apathy could have on academic performance. Carlson and Mann (2002) reported that children with ADHD-I and either low or high levels of SCT did not differ on measures of learning problems. However, SCT has been shown to be negatively associated with cognitive ability and academic achievement (Hartman, Willcutt, Rhee, & Pennington, 2004; Mikami et al., 2007; Wåhlstedt & Bohlin, 2010).
In sum, there is strong evidence that SCT is associated with co-occurring internalizing mental health symptoms and some evidence that SCT may be associated with social problems and academic difficulties. However, the limited number of studies precludes firm conclusions, and the data collected to date draw predominantly from samples of elementary school–age children or samples with a very wide age range (e.g., ages 3-18). It is particularly important to examine SCT among young adolescents because the transition to middle school is associated with unique difficulties and environmental demands for youth with ADHD (e.g., DuPaul & Stoner, 2003; Langberg et al., 2008). Therefore, the purposes of the present study were to (a) determine whether the relation found in previous research between SCT and internalizing symptoms exists in young adolescents with ADHD, (b) examine whether SCT is associated with social problems above and beyond the impact of ADHD and co-occurring externalizing behavior symptom severity, and (c) examine whether a relation between SCT and academic functioning exists above and beyond ADHD and co-occurring externalizing behavior symptom severity and intelligence. Consistent with the bulk of previous research, we hypothesized that SCT would be uniquely associated with internalizing symptoms and academic functioning above and beyond ADHD and oppositional defiant disorder/conduct disorder (ODD/CD) symptoms. In contrast, we hypothesized that SCT would not be associated with externalizing problems or social functioning after accounting for ADHD and ODD/CD behaviors.
Method
Participants
Participants were 57 youth (44 boys, 13 girls) ages 10 to 14 (M = 11.9, SD = 1.0). The majority of participants were European American (n = 40), with the remaining participants African American (n = 16) or biracial (n = 1). In all, 30 participants met Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV-TR; American Psychiatric Association, 2000) criteria for ADHD-I, and 27 met criteria for ADHD-Combined Type (ADHD-C). Using evidence-based recommendations for the assessment of ADHD (American Academy of Pediatrics, 2011; Pelham, Fabiano, & Massetti, 2005), ADHD diagnoses were established using a combination of a structured interview administered to the parent (Diagnostic Interview Schedule for Children-IV [DISC-IV]; Shaffer, Fischer, Lucas, Dulcan, & Schwab-Stone, 2000) and teacher ratings of ADHD symptoms on a DSM-based scale (Vanderbilt ADHD Diagnostic Teacher Rating Scale; Wolraich, Feurer, Hannah, Baumgaertel, & Pinnock, 1998). To be eligible for participation, students had to meet criteria for ADHD on the DISC-IV and have at least four symptoms in one domain endorsed as often or very often on the Teacher Rating Scale. In addition to meeting DSM-IV-TR criteria for a diagnosis of either ADHD-I or ADHD-C, youth were required to have an estimated Full Scale IQ ≥75, which was estimated using four subtests from the Wechsler Intelligence Scale for Children–Fourth Edition (Wechsler, 2003). Using the DISC-IV (Shaffer et al., 2000) to establish comorbid diagnoses, 27 participants met criteria for ODD or CD, 13 participants met criteria for an anxiety disorder, and 1 participant met criteria for a depressive disorder; no participants met criteria for mania.
Measures
Child Behavior Checklist for Ages 6-18 (CBCL/6-18)
The CBCL/6-18 is a well-validated parent-report measure of emotional and behavioral problems for youth ages 6 through 18 (Achenbach & Rescorla, 2001). Parents use a 3-point scale (0 = not true, 1 = somewhat or sometimes true, 2 = very true or often true) to indicate how true each item is for their child. T-scores on the CBCL SCT scale were used to measure SCT symptoms. Composed of four items (confused or seems to be in a fog, daydreams or gets lost in his/her thoughts, stares blankly, and underactive, slow moving, or lacks energy), this scale is reliable and distinct from measures of ADHD (e.g., Garner et al., 2010; Wåhlstedt & Bohlin, 2010). Furthermore, these four CBCL items are similar to the SCT items used in other studies (e.g., Hartman et al., 2004; McBurnett et al., 2001; Skirbekk et al., 2011).
The present study also used T-scores on the Internalizing (30 items; e.g., cries a lot, would rather be alone than with others, too fearful or anxious), Externalizing (27 items; e.g., breaks rules, argues a lot, gets in many fights), and Social Problems scales (11 items; e.g., complains of loneliness, doesn’t get along with other kids, not liked by other kids). It is important to note that none of these scales have items that also load onto the SCT scale. In the present study, SCT α = .66, Internalizing α = .80, Externalizing α = .89, and Social Problems α = .82.
Vanderbilt ADHD Diagnostic Parent Rating Scale (VADPRS).
The VADPRS is a parent-report scale with good internal consistency, factor structure, and concurrent validity for the assessment of ADHD and frequently comorbid conditions (Becker, Langberg, Vaughn, & Epstein, 2012; Wolraich et al., 2003). Parents rate how frequently each symptom occurs on a scale from 0 = never to 3 = very often. Five continuous VADPRS scores were used in the present study to assess mental health symptoms by summing items for each scale: Inattention (sum of 9 items), Hyperactivity/Impulsivity (9 items), Total ADHD (combined Inattention and Hyperactivity/Impulsivity), ODD/CD (22 items), and Anxiety/Depression (7 items). In the present study, Inattention α = .92, Hyperactivity/Impulsivity α = .96, Total ADHD α = .94, ODD/CD α = .93, and Anxiety/Depression α = .87.
Wechsler Individual Achievement Test–Third Edition (WIAT-III)
The WIAT-III is a frequently used standardized test of academic achievement demonstrated to be reliable and valid (Wechsler, 2009). In the present study, participants were administered the Reading, Spelling, and Math subtests, and standard scores on these subtests were used in analyses.
Homework Problem Checklist (HPC)
The HPC (Anesko, Schoiock, Ramirez, & Levine, 1987) is a 20-item parent-report measure. For each item, parents rate the frequency of a specific homework problem on a scale from 0 = never to 3 = very often. Factor analyses (Langberg et al., 2010; Power, Werba, Watkins, Angelucci, & Eiraldi, 2006) indicate that the HPC has two distinct factors: Factor I measures homework completion behaviors (12 items; e.g., doesn’t do homework unless someone is in the room, easily frustrated by homework assignment) and Factor II measures homework materials management behaviors (7 items; e.g., fails to bring home assignments and materials, forgets to bring assignment back to class). In the present study, Factor I α = .90 and Factor II α = .92.
Impairment Rating Scale (IRS)
The IRS (Fabiano et al., 2006) assesses the severity of a youth’s problems across multiple functional domains, and parent and teacher reports on the peer and academic domains were used in the present study. To complete the IRS, parents and teachers mark an “X” on a line indicating the severity of the youth’s impairment for each domain. Next, a scoring template is used to establish impairment severity on a scale from 0 = not a problem/definitely does not need treatment or special services to 6 = extreme problem/definitely needs treatment or special services. The IRS has demonstrated adequate psychometric properties and discriminates between children with and without ADHD (Fabiano et al., 2006). When multiple teachers completed the IRS, ratings were averaged to complete a single peer and academic impairment score.
Analytical Approach
We first examined whether SCT symptoms differed between participants with ADHD-I or ADHD-C, or between boys and girls. Next, bivariate correlations among the study variables were conducted. Finally, hierarchical regression analyses were conducted to test whether SCT was associated with mental health, social, or academic impairment above and beyond ADHD and ODD/CD symptom severity. Variables were only included in the regression analyses if they were significantly correlated with SCT in the bivariate analyses (p < .05).
Results
Independent samples t tests were used to examine whether SCT scores differed between youth with ADHD-I (M = 63.07, SD = 8.47) or ADHD-C (M = 62.96, SD = 7.60), or between boys (M = 62.45, SD = 8.09) and girls (M = 64.92, SD = 7.66). Results indicated that the two diagnostic groups did not differ, t(55) = 0.05, p = .96. Also, SCT scores did not differ between boys and girls, t(55) = 0.98, p = .33.
In addition to variable means and standard deviations, bivariate correlations among study variables are shown in Table 1 (mental health/social functioning) and Table 2 (academic functioning). SCT was significantly associated with inattention symptoms, but not hyperactive/impulsivity symptoms. In terms of other mental health domains, SCT was significantly associated with the CBCL Externalizing scale as well as the CBCL Internalizing scale and the VADPRS Anxiety/Depression scale. In domains of social functioning, SCT was significantly associated with the CBCL Social Problems scale, but not associated with either the parent- or teacher-reported peer impairment items on the IRS. SCT was not associated with any measure of academic functioning with the exception of the HPC Factor I scale, such that higher SCT scores were significantly associated with greater problems in homework completion.
Bivariate Correlations of SCT and Measures of Mental Health Symptoms and Social Functioning.
Note: CBCL = Child Behavior Checklist; IRS = Impairment Rating Scale; ODD/CD = oppositional defiant disorder/conduct disorder; SCT = sluggish cognitive tempo; VADPRS = Vanderbilt ADHD Diagnostic Parent Rating Scale.
p < .05. ** p < .01. *** p < .001.
Bivariate Correlations of SCT and Measures of Academic Functioning.
Note: CBCL = Child Behavior Checklist; HPC = Homework Problem Checklist; IRS = Impairment Rating Scale; SCT = sluggish cognitive tempo; VADPRS = Vanderbilt ADHD Diagnostic Parent Rating Scale; WISC = Wechsler Intelligence Scale for Children; WIAT = Wechsler Individual Achievement Test.
p < .05. ** p < .01. *** p < .001.
The five outcome variables that had significant bivariate correlations with SCT were entered separately into each regression model: VADPRS Anxiety/Depression, CBCL Internalizing, CBCL Externalizing, CBCL Social Problems, and HPC Factor I. ADHD severity was controlled for in every model. 1 In addition, ODD/CD symptoms were also controlled for in the VADPRS Anxiety/Depression, CBCL Internalizing, and CBCL Social Problems models (but not the CBCL Externalizing model given the significant overlap between ODD/CD symptoms and CBCL Externalizing). Finally, because IQ was negatively associated with HPC Factor I (but not the four other outcome variables), it was added as a covariate on Step 1 for the HPC Factor I model only.
Results of the regression analyses are summarized in Table 3. Above and beyond ADHD and ODD/CD symptoms, SCT was associated with both measures of internalizing symptoms, VADPRS Anxiety/Depression and CBCL Internalizing, as well as with CBCL Social Problems. SCT was not associated with externalizing symptoms above and beyond ADHD severity. SCT was not associated with HPC Factor I above and beyond the contributions of participant IQ and externalizing symptoms.
Multiple Regression Models Testing for SCT as a Predictor of Mental Health Symptoms, Social Problems, and Homework Completion.
Note: CBCL = Child Behavior Checklist; HPC = Homework Problems Checklist; ODD/CD = oppositional defiant disorder/conduct disorder; SCT = sluggish cognitive tempo; VADPRS = Vanderbilt ADHD Diagnostic Parent Rating Scale; WISC = Wechsler Intelligence Scale for Children. Beta weights reflect variables’ coefficients in the final model.
p < .05. **p < .01. ***p < .001.
Discussion
This study examined the relation between SCT symptoms, internalizing and externalizing symptoms, and functional impairment among young adolescents with ADHD. Given ongoing interest in the extent to which SCT is best subsumed under conceptualizations of ADHD or rather represents a distinct disorder (e.g., Barkley, 2011; Carlson & Mann, 2002; Garner et al., 2010; Harrington & Waldman, 2010; Hartman et al., 2004; McBurnett et al., 2001; Milich et al., 2001), it is essential to determine the degree to which SCT symptoms are associated with co-occurring mental health problems and functional impairment above and beyond the contribution of ADHD symptoms. In addition, it is important to document the ways in which SCT is associated with impairment across distinct developmental stages (e.g., Barkley, 2011). Although previous studies have used samples with a wide age range that encapsulated young adolescence, this is the first study to our knowledge that specifically examines the relation of SCT symptoms to multiple domains of functioning (i.e., mental health, social, academic) among young adolescents with ADHD.
Consistent with previous research, results of the present study demonstrate that SCT is positively related to internalizing mental health symptoms. Importantly, SCT was associated with two different measures of internalizing symptoms, and this relation remained significant above and beyond the contributions of ADHD and ODD/CD symptoms. Additional studies are needed to clarify the interrelations of ADHD (particularly inattention), SCT, and internalizing symptoms. For instance, Skirbekk and colleagues (2011) found that the relation between SCT and anxiety might be due to the presence of inattentive symptoms. In contrast, our results are consistent with those of Penny et al. (2009) in demonstrating that SCT is significantly associated with internalizing symptoms above and beyond ADHD and ODD/CD symptoms, as well as inattention symptoms specifically. 1 Methodological differences may be relevant in understanding these differences; whereas the present study used continuous measures of internalizing symptomatology, Skirbekk et al. (2011) used a semistructured interview to assign anxiety diagnoses. It is possible that SCT is related to the general degree of youths’ internalizing distress that parents observe but less related to DSM-based diagnoses that require, by definition, associated impairment to be established at the outset.
In contrast to internalizing symptoms, it appears that SCT is not uniquely associated with externalizing symptoms. Although SCT was correlated with one of the two measures of externalizing symptoms, this relation did not remain significant when controlling for ADHD symptoms. This is an important contribution to the literature to date. For example, Garner et al. (2010) reported a significant positive correlation between SCT and aggression, but the authors did not control for ADHD symptoms that are frequently co-occurring with such conduct problems. Generally, these and other results suggest that SCT falls along the internalizing, rather than externalizing, spectrum of psychopathology. As research accumulates suggesting SCT to be a unique disorder from ADHD (e.g., Barkley, 2011; Milich et al., 2001), it will be important to examine the causes, correlates, and consequences associated with SCT as it appears in isolation or co-occurs with internalizing and externalizing mental health problems.
In addition to mental health symptoms, results demonstrate that SCT is uniquely related to parent-reported social functioning broadly, consistent with previous research (Carlson & Mann, 2002; Garner et al., 2010), but not to parent- or teacher-reported impairment in peer relations specifically. Although the CBCL Social Problems scale includes several items specific to peer relationships (e.g., not liked by other kids, prefers being with younger kids), other items on this scale are specific to adult relationships (e.g., clings to adults or too dependent) or child responses to social experiences (e.g., complains of loneliness, easily jealous). In contrast, the IRS item is specific to impairment in the peer domain. More research is needed to examine the possibility that SCT is associated with broadband measures of social functioning, but not with peer relationship impairment specifically. It may be that SCT relates to parents’ general sense of their children’s social difficulties, likely due to missing social cues, but not to parents’ sense of peer-specific deficits given that SCT might reduce the more overt, hostile behaviors that draw the attention of adults (Mikami et al., 2007). In contrast, it is also possible that the findings reported here are due more to the use of the same measure for social problems and SCT, as well as the limitation of the one-item measurement of peer functioning on the IRS, rather than to differences across domains of social functioning.
Clearly, additional research also will be needed to clarify what relation, if any, SCT has to intelligence, academic achievement, and academic impairment. The present study did not find a significant correlation between SCT and either estimated IQ or academic achievement. Furthermore, SCT was correlated with only one of four measures of academic impairment, and the relation between SCT and homework completion did not remain significant when controlling for IQ or externalizing behavioral problems. This is an important extension of previous research. Although it is well established that ADHD is linked to longstanding academic difficulties (e.g., Fergusson, Boden, & Horwood, 2010; Pardini & Fite, 2010), other studies have not examined whether SCT predicts academic impairment above and beyond the contribution of ADHD symptoms.
Several limitations of the present study should be noted. First, although the measure of SCT employed in the present study has been used extensively in SCT research to date, the internal consistency of this scale in our sample was relatively poor, and other validated measures that distinguish between various factors of SCT may reveal distinct associations (e.g., Penny et al., 2009). Relatedly, only parent-reported SCT symptoms were measured, and teachers are important reporters of SCT given the potential effects that daydreaming, sluggish, and sleepy behavior have on classroom performance and peer relations (Garner et al., 2010). Crucially, no studies to date have examined the predictive relation between SCT and subsequent impairment. In addition, although the focus on young adolescents with ADHD is a contribution to the limited number of studies to date examining this age range, results may not generalize to younger or older populations of youth with ADHD, other clinical diagnoses, or community youth.
In sum, SCT is associated with internalizing mental health symptoms and social functioning among young adolescents with ADHD, and these relations remain present after controlling for ADHD and ODD/CD symptoms. In contrast, the association between SCT and externalizing problems or academic functioning, if present, is reduced to nonsignificance when accounting for other relevant factors such as ADHD symptomatology and intelligence. Future work is needed to replicate these findings, in addition to examining specific facets of internalizing symptoms (e.g., anxiety, depression) and social functioning (e.g., social competence, peer relations). Last, this study used a sample of young adolescents diagnosed with ADHD, and the ongoing study of SCT will be greatly informed by additional studies that document the correlates and longitudinal impairments that are linked to SCT across development, as well as studies that compare individuals with and without ADHD.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Funding for this study was provided by the Institute of Education Sciences (IES; R305A090305).