Validity of the Sluggish Cognitive Tempo Symptom Dimension in Children: Sluggish Cognitive Tempo and ADHD-Inattention as Distinct Symptom Dimensions

This study examined the validity of the sluggish cognitive tempo (SCT) symptom dimension in children. Ten symptom domains were used to define SCT (i.e., (1) daydreams; (2) attention fluctuates; (3) absent-minded; (4) loses train of thought; (5) easily confused; (6) seems drowsy; (7) thinking is slow; (8) slow-moving; (9) low initiative; and (10) easily bored, needs stimulation). Teacher ratings of 366 children (ages 5 to 13 with 56 % girls) along with parent ratings of 703 children (ages 5 to 13 with 55 % girls) indicated that SCT symptom domains one to eight showed convergent validity (i.e., substantial loadings on the SCT factor) and discriminant validity with the ADHD-IN dimension (i.e., higher loadings on the SCT factor than the ADHD-IN factor). Higher scores on this eight-symptom measure of SCT predicted lower levels of academic and social competence even after controlling for ADHD-IN and ADHD-HI. In addition, higher SCT scores still predicted higher anxiety/depression scores after controlling for ADHD-IN and ADHD-HI. Higher SCT scores also predicted lower ADHD-HI scores after controlling for ADHD-IN and anxiety/depression while higher ADHD-IN and anxiety/depression scores predicted higher ADHD-HI scores after controlling for SCT and anxiety/depression or ADHD-IN. SCT also showed a unique negative relationship with ODD while ADHD-IN and anxiety/depression showed unique positive relationships with ODD. This new measure of the SCT dimension was meaningfully independent from the ADHD-IN and anxiety/depression dimensions and suggests that such an SCT dimension may signify a distinct presentation of ADHD or a different (if highly comorbid) disorder altogether.     

Executive Functioning, Temporal Discounting, and Sense of Time in Adolescents with Attention Deficit Hyperactivity Disorder (ADHD) and Oppositional Defiant Disorder (ODD)

Clinic-referred teens (ages 12–19) with ADHD and ODD (N = 101) were compared to community control (CC) teens, equated for age and sex, (N = 39) on a variety of psychological tasks assessing executive functioning (EF), temporal reward discounting, and time estimation and reproduction. A factor analysis reduced the EF measures to three dimensions, representing CPT Inattention, Working Memory, and CPT Inhibition. Results indicated that the ADHD group had significantly more CPT Inattention than the CC group. No differences were found for Working Memory or CPT Inhibition. The ADHD group displayed significantly greater temporal discounting of delayed hypothetical monetary rewards relative to immediate ones and manifested more impaired time reproduction, but not time estimation, than did the CC group. Main effects for level of IQ were found only on the Working Memory factor and largely did not interact with the group factor otherwise. The group differences in CPT Inattention, temporal discounting, and time reproduction were not a function of level of comorbid oppositional defiant disorder, delinquency, or anxiety–depression. Results are reasonably consistent with past research on EF and sense of time in children with ADHD and extend these findings to the adolescent age group. Problems with working memory and CPT inhibition found in prior studies of children with ADHD, however, were not evident here, perhaps owing to age-related improvements or insufficient task difficulty.     

Sluggish Cognitive Tempo in Psychiatrically Hospitalized Children: Factor Structure and Relations to Internalizing Symptoms, Social Problems, and Observed Behavioral Dysregulation

As research examining sluggish cognitive tempo (SCT) advances, it is important to examine the structure and validity of SCT in a variety of samples, including samples of children who are clinically-distressed but not referred specifically for attention-deficit/hyperactivity disorder (ADHD). The present study used a large sample of psychiatrically hospitalized children (N?=?680; 73 % male; 66 % African American) between the ages of 6 and 12 to examine the latent structure of SCT, ADHD, oppositional defiant disorder (ODD), depression, and anxiety using confirmatory factor analysis (CFA). Results of the CFA analyses demonstrated that SCT is distinct from these other dimensions of child psychopathology, including ADHD inattention, depression, and anxiety. Regression analyses indicated that SCT symptoms were positively associated with depression and, to a lesser degree, anxiety. SCT symptoms were also positively associated with children’s general social problems, whereas SCT symptoms were negatively associated with an observational measure of behavioral dysregulation (i.e., frequency of time-outs received as a part of a manualized behavior modification program). These associations were significant above and beyond relevant child demographic variables (i.e., age, sex, race), children’s other mental health symptoms (i.e., ADHD, ODD, depression, anxiety symptoms), and, for all relations except child anxiety, parents’ own anxiety and depression symptoms.     

Internal and External Validity of Sluggish Cognitive Tempo and ADHD Inattention Dimensions with Teacher Ratings of Nepali Children

The objective was to evaluate the validity of sluggish cognitive tempo (SCT) and ADHD-inattention (IN) symptoms in children from Nepal. Teachers rated SCT, ADHD-IN, ADHD-hyperactivity/impulsivity (HI), oppositional defiant disorder (ODD), anxiety, depression, academic impairment, social impairment, and peer rejection dimensions in 366 children (50 % girls) in first through sixth grades (M _age?=?9.35, SD _age?=?1.96) on two separate occasions separated by 4-weeks. Seven of the eight SCT symptoms and all nine ADHD-IN symptoms showed convergent validity (substantial loadings on their respective factors) and discriminant validity (higher loadings on their respective factor than the alternative factor) at both time-points. Across all three separate analyses (assessment 1, assessment 2, and from assessment 1 to assessment 2), higher SCT scores were associated with lower ADHD-HI scores and higher depression, academic impairment, and social impairment scores after controlling for ADHD-IN while higher ADHD-IN scores were associated with higher ADHD-HI, ODD, academic impairment, and peer rejection scores after controlling for SCT. Also, as hypothesized, SCT scores were not related to ODD scores after controlling for ADHD-IN. The study provides the first evidence for the internal and external validity of the SCT dimension relative to the ADHD-IN dimension with teacher ratings of children from Nepal, thereby increasing the validity of the SCT construct beyond North America, Western Europe, South America, and South Korea.     

Sequenced neurocognitive and behavioral parent training for the treatment of ADHD in school-age children

The present study examines the potential of sequencing a neurocognitive intervention with behavioral parent training (BPT) to improve executive functions (EFs), psychiatric symptoms, and multiple indices of functional impairment in school-age children aged 7 to 11 years who have been diagnosed with attention-deficit/hyperactivity disorder (ADHD). Specifically, in a randomized controlled trial design, 85 children were assigned to either Cogmed Working Memory Training (CWMT) followed by an empirically supported, manualized BPT intervention, or to a placebo version of CWMT followed by the same BPT intervention. Working memory maintenance (i.e., attention control/short-term memory), working memory processing and manipulation, ADHD and oppositional defiant disorder (ODD) symptoms, impairment in parent–child dynamics, familial impairment, and overall functional compromise were evaluated as outcomes. The results suggest specific effects of the combined CWMT and BPT program on verbal and nonverbal working memory storage and nonverbal working memory processing and manipulation but no incremental benefits in regard to ADHD symptoms, ODD symptoms, and functional outcomes. The present findings do not support the hypothesis regarding the complementary and augmentative benefits of sequenced neurocognitive and BPT interventions for the treatment of ADHD. These results, the study’s limitations, and future directions for research are further discussed.     

Factor Structure of a Sluggish Cognitive Tempo Scale in Clinically-Referred Children

“Sluggish cognitive tempo” (SCT) is a construct hypothesized to describe a constellation of behaviors that includes daydreaming, lethargy, drowsiness, difficulty sustaining attention, and underactivity. Although the construct has been inconsistently defined, measures of SCT have shown associations with symptoms of attention-deficit/hyperactivity disorder (ADHD), particularly inattention. Thus, better characterization of SCT symptoms may help to better predict specific areas of functional difficulty in children with ADHD. The present study examined psychometric characteristics of a recently developed 14-item scale of SCT (Penny et al., Psychological Assessment 21:380–389, 2009), completed by teachers on children referred for outpatient neuropsychological assessment. Exploratory factor analysis identified three factors in the clinical sample: Sleepy/Sluggish, Slow/Daydreamy, and Low Initiation/Persistence. Additionally, SCT symptoms, especially those loading on the Sleepy/Sluggish and Slow/Daydreamy factors, correlated more strongly with inattentive than with hyperactive/impulsive symptoms, while Low Initiation/Persistence symptoms added significant unique variance (over and above symptoms of inattention) to the predictions of impairment in academic progress.     

ODD dimensions, ADHD, and callous-unemotional traits as predictors of treatment response in children with disruptive behavior disorders

To answer several questions pertinent to DSM-V, the authors examined the predictive validity of pretreatment oppositional defiant disorder (ODD) dimensions, attention-deficit/hyperactivity disorder (ADHD), and callous-unemotional (CU) traits in relation to several treatment outcomes in 177 children diagnosed with ODD or conduct disorder (CD). Multiple informants completed diagnostic interviews and rating scales at 6 assessment points (pretreatment to 3-year follow-up) to document emotional and behavioral outcomes. After controlling for pretreatment CD, the ODD dimension of hurtfulness was related to treatment-resistant CD, delinquent behaviors, and externalizing problems. In contrast, the ODD dimension tapping irritability was associated with treatment-resistant ODD, internalizing problems, and global functional impairment following treatment. Whereas pretreatment ADHD was associated with posttreatment ODD and social problems, it was unrelated to posttreatment CD symptoms and diagnosis. Contrary to predictions, CU traits were unrelated to any posttreatment outcomes after controlling for other covariates. These findings remained after controlling for measures of pretreatment global functional impairment.     

A Cross-Sectional and Longitudinal Investigation of the External Correlates of Sluggish Cognitive Tempo and ADHD-Inattention Symptoms Dimensions

The objective was to determine if the external correlates of sluggish cognitive tempo (SCT) and ADHD-inattention (IN) dimensions were the same in cross-sectional and longitudinal analyses. Teachers and aides rated SCT, ADHD-IN, ADHD-hyperactivity/impulsivity (HI), oppositional defiant disorder (ODD), and depression along with academic impairment in 758 Spanish children (55 % boys) on three occasions (twice at the end of the first grade year [6-week separation] and then again 12-months later at the end of the second grade year). Three of eight SCT symptoms showed substantial loadings on the SCT factor and substantially higher loadings on the SCT factor than the ADHD-IN factor for teachers and aides at each assessment (seems drowsy, thinking is slow, and slow moving). Cross-sectional and longitudinal analyses yielded similar results with SCT and ADHD-IN factors having different and unique external correlates (higher scores on SCT predicted lower scores on ADHD-HI and ODD while higher scores on ADHD-IN predicted higher scores on ADHD-HI and ODD with SCT and ADHD-IN both uniquely predicting academic impairment and depression). Developmental and methodological reasons are discussed for the failure to find an inconsistent alertness SCT factor (daydreams, alertness fluctuates, absent-minded, loses train of though, and confused).     

Few Preschool Boys and Girls with ADHD are Well-Adjusted During Adolescence

To estimate the prevalence of being well-adjusted in adolescence, boys and girls with (n = 96) and without (n = 126) attention-deficit/hyperactivity disorder (ADHD) were assessed seven times in eight years starting when they were 4–6 years of age. Symptoms of ADHD, ODD/CD, and depression/anxiety in addition to social skills and social preference were gathered using multiple methods and informants. Being well-adjusted was defined by surpassing thresholds in at least four of the five domains. At the 7- and 8-year follow-up, when youth were 11–14 years old, probands were significantly less likely to be well-adjusted relative to age- and ethnicity-matched control children. Only a minority of children with ADHD was well-adjusted in adolescence when emotional, behavioral, and social domains were considered simultaneously. Even when their ADHD symptoms improved over time, most probands exhibited significant impairment 7–8 years after their initial assessment.     

The Association Between Sluggish Cognitive Tempo and Academic Functioning in Youth with Attention-Deficit/Hyperactivity Disorder (ADHD)

The purpose of the study was to evaluate the relation between Sluggish Cognitive Tempo (SCT) and academic functioning in a sample of 52 adolescents (40 males, 12 females) with Attention-Deficit/Hyperactivity Disorder (ADHD; M _age?=?13.75). This study builds on prior work by utilizing an empirically-based and psychometrically validated measure of SCT, collecting ratings of SCT from both parents and teachers, and examining associations with multiple domains of academic functioning from both the parent and teacher perspective as well as grade point average (GPA). Both SCT and DSM-IV symptoms of inattention were significantly correlated with domains of academic functioning. Multiple regression analyses demonstrated that the parent-rated SCT Slow subscale predicted overall academic functioning, organizational skills impairment, and homework problems above and beyond ADHD symptoms and child and demographic characteristics known to be associated with academics, including intelligence, academic achievement, and family income. The teacher-rated SCT Low Initiation/Persistence subscale also predicted homework problems and was the only SCT variable to predict school grades above and beyond ADHD symptoms and relevant covariates. Both the SCT Slow and Low Initiation/Persistence subscales include items related to youth seeming apathetic, unmotivated, and lacking initiative, behaviors that are strongly related to ADHD symptoms of inattention but not currently captured by the DSM-IV. Implications of these findings towards supporting the external validity of the SCT construct are discussed along with potential implications for intervention.     

Examining Anxiety and Depression as Moderators of the Associations Between ADHD Symptoms and Academic and Social Problems in Hispanic Adolescents

The effects of attention-deficit/hyperactivity disorder (ADHD) symptoms on the psychosocial functioning of Hispanic youth have been understudied. It also remains unclear if the well-established associations between ADHD symptoms and academic and social impairment are exacerbated by co-occurring internalizing symptoms. The purposes of the present study were to (1) examine whether ADHD symptoms would be associated with academic and social problems while also controlling for oppositional defiant disorder (ODD) symptoms, and (2) test the hypothesis that anxious and depressive symptoms would moderate the relations between ADHD symptoms and academic and social problems. Participants were 142 at-risk Hispanic adolescents (54 % male, ages 14–19) who reported on their anxious and depressive symptoms, as well as their teachers who reported on adolescents’ ADHD symptoms, ODD symptoms, academic problems, and social problems. When the psychopathology variables were included simultaneously in a path model, ADHD was the only domain significantly positively associated with academic problems. In contrast, ODD and depressive symptoms were the only domains significantly positively associated with social problems when all of the psychopathology variables were included in the path model. No moderation effects were found in relation to academic problems, although a significant ADHD × depression interaction was found in relation to social problems. Specifically, ADHD symptoms were not associated with social problems among adolescents who reported low levels of depressive symptoms, but the association between ADHD symptoms and social problems was significant at higher levels of depression. In addition to targeting oppositionality, attending to the combined presence of ADHD and depressive symptoms will be important for reducing the social impairments among Hispanic adolescents.     

Attention Deficit-Hyperactivity Disorder, Depression, and Self- and Other-Assessments of Social Competence: A Developmental Study

This study examined whether others (i.e., teachers and parents) and self-appraisals of social competence mediated the relationship between Attention-Deficit/Hyperactivity Disorder (ADHD) and depression. To determine whether age moderated the effects of the mediation, the total sample was divided into younger (under 9) and older (at or above 9 years) age levels. The total sample (age range 6.6 to 11.7 years) was primarily male (194 boys and 52 females) and consisted of 148 children diagnosed with ADHD and 98 community controls. Three central findings were derived from this study. First, there was a strong relationship between ADHD (with and without comorbid ODD/CD) and depression in both younger and older aged children. Among younger children with ADHD, there was no differential influence on the level of depression depending on whether or not ADHD was comorbid with ODD/CD; in contrast, with older children, comorbid ODD/CD had higher levels of depression than was the case for children with ADHD that did not display such comorbidity. Second, with younger children approximately half of the relationship between ADHD (with and without comorbid ODD/CD) and depression was exclusively mediated by others appraisal of social competence. Third, a more complex relationship between ADHD and depression emerged during the later part of the childhood years. As such, the relationship between ADHD, others appraisals of social competence, and depression was further mediated by self-appraisals of social competence. Findings are discussed in terms of developmental theory and theoretical models of childhood depression.Rick Ostrander and David S. Crystal contributed equally to this article, and the order of authorship was determined by a coin toss.     

Evidence for the Trait-Impulsivity Etiological Model in a Clinical Sample: Bifactor Structure and Its Relation to Impairment and Environmental Risk

The trait-impulsivity etiological model assumes that a general factor (trait-impulsivity) underlies attention-deficit/hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and other externalizing disorders. We investigated the plausibility of this assumption by testing the factor structure of ADHD and ODD in a bifactor framework for a clinical sample of 1420 children between 6 and 18 years of age (M = 9.99, SD = 3.34; 85% male). Further, the trait-impulsivity etiological model assumes that ODD emerges only if environmental risk factors are present. Our results support the validity of the trait-impulsivity etiological model, as they confirm that ADHD and ODD share a strong general factor of disruptive behavior (DB) in this clinical sample. Furthermore, unlike the subdimensions of ADHD, we found that the specific ODD factor explained as much true score variance as the general DB factor. This suggests that a common scale of ADHD and ODD may prove to be as important as a separate ODD subscale to assess externalizing problems in school-age children. However, all other subscales of ADHD may not explain sufficient true score variance once the impact of the general DB factor has been taken into consideration. In accordance with the trait-impulsivity model, we also showed that all factors, but predominantly the general factor and specific inattention factor, predicted parent-rated impairment, and that predominantly ODD and impulsivity are predicted by environmental risk factors.     

Dimensions and Correlates of Attention Deficit/Hyperactivity Disorder and Sluggish Cognitive Tempo

The present study examined Sluggish Cognitive Tempo (SCT) in relation to ADHD symptoms, clinical diagnosis, and multiple aspects of adjustment in a clinical sample. Parent and teacher reports were gathered for 322 children and adolescents evaluated for behavioral, emotional, and/or learning problems at a university clinic. Confirmatory factor analyses (CFA) supported the presence of three separate, but correlated factors (SCT, inattention, and hyperactivity/impulsivity) in both parent and teacher ratings. As expected, SCT symptoms were greatest in youth with ADHD Inattentive type, but were also found in non-ADHD clinical groups. SCT symptoms were related to inattention, internalizing, and social problems across both parent and teacher informants; for parent reports, SCT was also related to more externalizing problems. Findings support the statistical validity of the SCT construct, but its clinical utility is still unclear.     

Children with ADHD and depression: a multisource, multimethod assessment of clinical, social, and academic functioning

Although ADHD and depression are common comorbidities in youth, few studies have examined this particular clinical presentation. To address method bias limitations of previous research, this study uses multiple informants to compare the academic, social, and clinical functioning of children with ADHD, children with ADHD and depression, and children without ADHD, all derived from a large community sample. High levels of comorbid depression are found in children with ADHD. Children withADHDand depression are more depressed and anxious than their non-depressed ADHDcounterparts but do not have more extreme levels of ADHD or aggression. The association between depression and ADHD does not appear to be epiphenomenal, that is, related to a shared association with anxiety or externalizing symptoms. Finally, children with ADHD and depression display more impairment in social and academic functioning compared to controls. Although social impairment is greater in children with ADHD and depression than in children with only ADHD, conduct problems are not.     

Longitudinal Evaluation of the Role of Academic and Social Impairment and Parent-Adolescent Conflict in the Development of Depression in Adolescents with ADHD

Older adolescents with attention-deficit/hyperactivity disorder (ADHD) have a significantly increased likelihood of developing comorbid depression. It is important to evaluate factors during the early adolescent period that may contribute to this risk. A predominant theory is that impairment and failure experiences lead to the development of low-self efficacy and depression, and that parent and family factors also play a role. In a sample of 326 young adolescents with ADHD (Mage?=?12), the present study evaluated whether parent-adolescent conflict mediated the association between social and academic impairment and the development of depression. This study builds upon prior work by evaluating these associations longitudinally and by using a multi-rater approach, including the parent, adolescent, and teacher perspectives. Social and academic impairment directly predicted depression controlling for baseline levels of depression and change in ADHD symptoms. The association between social impairment and depression was partially mediated by parent-adolescent conflict. Mediation through conflict was not found for academic impairment, and the association between academic impairment and depression was no longer significant when accounting for conflict. These findings highlight the importance of social impairment in the development of depression in adolescents with ADHD. Caregivers may play an important role in determining whether adolescents with ADHD internalize social impairment and failure experiences and develop depressive symptoms. Implications of these findings in terms of the importance of interventions focused on parent-adolescent conflict are discussed.     

Waxing and waning in concert: dynamic comorbidity of conduct disorder with other disruptive and emotional problems over 7 years among clinic-referred boys

Six waves of structured diagnostic assessments were conducted of 168 clinic-referred 7- to 12-year-olds, over 7 years. Wave-to-wave changes in the number of conduct disorder (CD) behaviors were paralleled by correlated changes in the numbers of symptoms of oppositional defiant disorder (ODD), attention-deficit/hyperactivity disorder (ADHD), depression, and anxiety. In addition, CD in Wave 1 predicted levels of ODD, ADHD, depression, and anxiety in later waves when initial levels of those symptoms were controlled, but only ODD in Wave 1 predicted CD in later waves when initial CD levels were controlled. These findings indicate a striking degree of dynamic comorbidity between CD and other types of psychopathology and provide an initial empirical framework for needed developmental models of comorbidity.     

The Internal and External Validity of Sluggish Cognitive Tempo and its Relation with DSM–IV ADHD

Studies of subtypes of DSM-IV attention-deficit/hyperactivity disorder (ADHD) have provided inconsistent support for the discriminant validity of the combined type (ADHD-C) and predominantly inattentive type (ADHD-I). A large sample of children and adolescents with ADHD (N?=?410) and a comparison group without ADHD (N?=?311) were used to test the internal and external validity of sluggish cognitive tempo (SCT), a dimension characterized by low energy and sleepy and sluggish behavior. SCT scores were then incorporated in analyses of ADHD subtypes to test whether the discriminant validity of ADHD-C and ADHD-I could be improved by including SCT symptoms as part of the criteria for ADHD-I. Factor analyses of parent and teacher ratings indicated that six SCT items loaded on a factor separate from symptoms of ADHD and other psychopathology, providing important support for the internal validity of SCT. The external validity of SCT was supported by significant associations between SCT and measures of functional impairment and neuropsychological functioning when symptoms of ADHD and other psychopathology were controlled. However, contrary to initial predictions, high levels of SCT did not identify a subgroup of ADHD-I that was clearly distinct from ADHD-C. Instead, the current results suggest that DSM-IV inattention and SCT are separate but correlated symptom dimensions that are each independently associated with important aspects of functional impairment and neuropsychological functioning.     

Measuring Emotion Dysregulation in Children With Attention-Deficit/Hyperactivity Disorder: Revisiting the Factor Structure of the Emotion Regulation Checklist

Emotion dysregulation (ED) is prevalent among youth with Attention-Deficit/Hyperactivity Disorder (ADHD) and significantly impacts functioning. Nuanced measurement of ED is central to understanding its role in this disorder and informing treatment approaches. The present study examined the factor structure of the Emotion Regulation Checklist (ERC) among children with ADHD with and without Oppositional Defiant Disorder (ODD). Exploratory factor analysis (EFA) conducted in a sample of 328 youth (mean age = 6.08) with ADHD indicated a four-factor solution, comprised of the following factors: Negative Emotion Lability, Positive Emotion Lability, Socially Appropriate Affect, and Socially Incongruent Affect. The Negative and Positive Emotion Lability subscales assess the reactivity of negatively and positively valenced emotions, respectively. The Socially Appropriate and Socially Incongruent Affect subscales provide an assessment of social-emotional functioning. All subscales discriminated between children with ADHD only and ADHD with co-morbid ODD, such that children with ODD had greater emotional lability and social-emotional difficulties. This revised factor structure of the ERC facilitates a uniquely brief, yet multifaceted and specific, assessment of emotional difficulties in children with ADHD that can inform treatment planning and operationalize emotional reactivity and social-emotional functioning in future research efforts.     

Sluggish Cognitive Tempo Symptoms Contribute to Heterogeneity in Adult Attention-Deficit Hyperactivity Disorder

Attention-deficit hyperactivity disorder (ADHD) persists into adulthood in over 50% of cases, although its associated symptom profiles, comorbid problems, and neuropsychological deficits change substantially across development. Sluggish cognitive tempo (SCT) symptoms may contribute to associations between ADHD and comorbid problems and may partially explain the substantial heterogeneity observed in its correlates. 349 adults aged 18–38 years (M = 23.2, SD = 4.5, 54.7% male, 61.03% with ADHD) completed a multi-informant diagnostic procedure and a comprehensive neuropsychological battery. Adults with ADHD (n = 213) were retained for analyses. Latent class analyses (LCA) revealed three profiles of SCT symptoms among those with ADHD, which we classified as minimal, moderate, or severe SCT. Multiple analysis of covariance (MANCOVA) revealed significant differences among these profiles, which remained when controlling for persistence of ADHD symptoms and sex. In general, adults with ADHD combined with SCT symptoms (moderate and severe) had significantly more symptoms of anxiety, depression, and persistent inattention, and had more severe professional and relational impairment compared to ADHD adults without SCT. Compared to those with moderate or minimal SCT symptoms, the severe SCT group had the most symptoms of depression and internalizing disorders, and the most impairment in the domain of daily responsibility. No significant differences based on externalizing symptoms emerged when controlling for sex and persistence of inattention symptoms, suggesting the moderate and severe SCT groups do not simply reflect more symptoms. Moreover, follow-up mediation analyses revealed that SCT might at least partially explain the heterogeneity in ADHD. Findings have implications for refinement of etiological conceptualization, assessment methods, and intervention strategies.