Attention-deficit/hyperactivity disorder (ADHD) and disruptive behavior disorders such as oppositional defiant disorder (ODD) and conduct disorder (CD) with its specifier for callous-unemotional (CU) traits are common and highly impairing mental disorders in childhood and adolescence (Herpers et al.,
2012; Polanczyk et al.,
2015). In the field of disruptive behavior disorders, symptoms of affective dysregulation have gained increasing attention in recent years. Yet, diagnostic classification systems still disagree in the assignment to diagnostic categories. While symptoms of affective dysregulation are conceptualized as core to the diagnosis of disruptive mood dysregulation disorder (DMDD) diagnosis in the 5
th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; American Psychiatric Association,
2013) and in the 10
th edition of the International Classification of Diseases (ICD-10; World Health Organization,
1992), the ICD-11 (World Health Organization,
2019) confines to adding a specifier for chronic irritability/anger to the ODD diagnosis because of the difficulty in empirically distinguishing DMDD from other mental disorders, particularly ADHD and ODD (Evans et al.,
2017; Lochman et al.,
2015). According to both classification systems, the diagnosis of any of these mental disorders requires the presence not only of symptoms with a certain frequency and severity, but also of functional impairment (FI). Although symptoms and FI are often interrelated, they are not identical (Palermo et al.,
2008). FI manifests across a wide range of domains and can be defined as
“the extent of restriction in a child’s ability to perform important daily life activities including physical, social, and personal activities due to their health condition or to specific symptoms” (Palermo et al.,
2008, p. 984). For example, the presence and severity of symptoms may interfere with children’s ability to attend school or to maintain friendships. In fact, many children and adolescents or their parents seek help because of FI rather than the presence of symptoms (Epstein & Weiss,
2012). Studies assessing the relationship between symptoms and FI have yielded mostly moderate associations (reviewed by Rapee et al.,
2012). In line with this, not all individuals meeting the symptom criteria for an ADHD or ODD/CD diagnosis demonstrate FI as a result of their symptoms, while others with only subthreshold symptoms may show marked levels of impairment (Arildskov et al.,
2022; DuPaul et al.,
2014; Pickles et al.,
2001). The assessment of FI is not only important for making diagnoses and verifying the need for treatment, but also for treatment planning, identifying maintaining factors of psychiatric symptoms and treatment targets, and evaluating treatment success (DuPaul,
2022; Haack & Gerdes,
2011; Winters et al.,
2005). Therefore, measures of FI provide important additional information to measures of symptoms.
Relationship between Symptom Dimensions and Functional Impairment Domains
Previous studies have demonstrated considerable variability in how symptom dimensions (e.g. ADHD inattention, hyperactivity-impulsivity) relate to various domains of FI. With regard to ADHD, the findings generally suggest that the inattention dimension is especially associated with academic impairment (Garner et al.,
2013; Massetti et al.,
2008; Willcutt et al.,
2012; Zoromski et al.,
2015). By comparison, the ADHD hyperactivity-impulsivity dimension generally shows the strongest associations with impaired social functioning, e.g. in the form of classroom disruption or peer exclusion (Garner et al.,
2013; Willcutt et al.,
2012). In terms of symptoms of disruptive behavior disorders, previous findings generally suggest that a greater severity of ODD problems is particularly related to impaired relationships with peers and family members (Burke et al.,
2014; Dose et al.,
2019; Kernder et al.,
2019). Similarly, CD problems were found to predict workplace problems in young adults (Burke et al.,
2014), and CU traits were found to predict impaired social functioning in children (Haas et al.,
2018). Notably, most of these associations remained significant after controlling for demographic factors and comorbid symptoms (Burke et al.,
2014; Garner et al.,
2013; Haas et al.,
2018; Massetti et al.,
2008; Power et al.,
2017; Willcutt et al.,
2012).
Yet, despite the growing body of literature on FI associated with symptoms of ADHD and disruptive behavior disorders, there is still a need for clarification regarding the relationship between
individual symptoms and different domains of FI. For example, it remains unclear whether certain symptoms are more impairing than others, and if so, what the relative importance of these symptoms is compared to other symptoms. This gap in the research is highly clinically relevant given the large variability in the symptoms experienced by patients (Mota & Schachar,
2000; Zoromski et al.,
2015).
Relationship between Individual Symptoms and Global Functional Impairment
To address this need for clarification, some studies have investigated the impact of individual symptoms, rather than symptom dimensions, on global FI. With respect to ADHD, Mota and Schachar (
2000) suggested that some individual ADHD symptoms, including, for example, the teacher-rated
leaves seat and the parent-rated
blurts out, predict global FI in children better than other symptoms. In a more recent study, Zoromski et al. (
2015) examined teacher ratings and found that certain symptoms of inattention (i.e.
does not listen during early childhood,
does not follow through during adolescence) and certain symptoms of hyperactivity-impulsivity (i.e.
on the go during early childhood,
leaves seat during middle childhood,
interrupts or intrudes during adolescence) showed the most robust relationships with classroom impairment. Regarding other externalizing behavior problems, research has shown that particularly ODD symptoms reflecting irritability (e.g.
anger and
temper outbursts) are associated with FI in children (Kolko & Pardini,
2010; Wesselhoeft et al.,
2019) and that these symptoms predict greater FI than do other symptoms, even after controlling for other mental disorders (Dougherty et al.,
2015). While this previous work has provided valuable insights into the relationship between symptoms and FI, additional exploration is needed. In particular, in previous studies, ratings for various domains of FI were combined into an overall, global score (Dougherty et al.,
2013,
2015; Mota & Schachar,
2000) or the assessment of impairment was limited to classroom settings (Zoromski et al.,
2015). A more nuanced approach, which considers the associations between individual symptoms and different FI domains in more detail while simultaneously accounting for ADHD as well as ODD, CD, and CU symptoms within a common approach, could help to enhance the understanding of these probably complex interrelations.
Network Analysis
Network analysis offers such a more nuanced approach, which could potentially uncover individual symptom relations and associations with different FI domains (Borsboom & Cramer,
2013). From a network perspective, mental disorders are conceptualized as networks of mutually interacting symptoms (Borsboom & Cramer,
2013). Psychological networks may be depicted as structures comprising nodes (e.g. symptoms, FI domains), which are connected via edges (e.g. positive or negative associations). Some nodes can have a more dominant, central position in a network, for example, as expressed by stronger connections with other nodes (Borsboom & Cramer,
2013; Epskamp et al.,
2018). Moreover, network analysis helps to uncover the unique strongest connections between nodes by relying on regularized partial correlations. This approach is somewhat similar to conducting multiple linear regressions at once, but with the advantage of reducing the risk of false positives (Epskamp & Fried,
2018). Hence, it is possible to determine which individual symptom shows the strongest association with a particular FI domain.
In recent years, many studies have applied network analysis to investigate how symptoms of different mental disorders are interrelated, particularly in the fields of anxiety and mood-related disorders (reviewed by Contreras et al.,
2019). In the field of externalizing disorders, network analysis has been applied to symptoms of ADHD (Burns et al.,
2022; Goh et al.,
2020,
2021a,
b; Martel et al.,
2016,
2021; Preszler et al.,
2020; Silk et al.,
2019), ODD (Smith et al.,
2017), or ADHD and ODD together (Martel et al.,
2017; Preszler & Burns,
2019), to CU traits (Bansal et al.,
2020; Deng et al.,
2021), and to CU traits in conjunction with ODD and CD (Bansal et al.,
2021), in samples ranging from preschool age to adulthood. Furthermore, a recent study explored the relations between ADHD symptoms, executive functioning, and temperament traits, and found support for the primary role of effortful control as a potential risk marker for the characterization of ADHD across childhood and adolescence (Goh et al.,
2021a,
b).
To the best of our knowledge, so far, only three studies have focused on the associations between ADHD symptoms and different FI domains using network analysis (Burns et al.,
2022; Goh et al.,
2020,
2021a,
b). Goh et al. (
2020) explored individual ADHD and sluggish cognitive tempo symptoms and their relations with multiple domains of FI in a nationally representative sample of 1,742 children and adolescents (age:
M = 11.51,
SD = 3.36, range 6 – 17 years). The results revealed that in particular, the following eight symptoms were related to various FI domains and especially to the domains of academic and social impairment:
difficulties following through on instructions, inability to stay seated, acting without thinking, impatience, disinhibition, apathy/withdrawal, slowness, and
lacking initiative. Similarly, Goh et al., (
2021a,
b) explored individual ADHD symptoms (with an expanded impulsivity set) and their relations with multiple FI domains using network analysis and random forest regression in a nationally representative sample of 1,249 adults. The results from both techniques revealed that in particular, three inattention symptoms (
difficulty organizing, does not follow through, makes careless mistakes) and one hyperactivity symptom (
difficulty engaging in leisure activities) were strongly associated with global FI and FI, especially in the domains of social and interpersonal relationships, and difficulties maintaining structure in daily life. Finally, Burns et al. (
2022) applied network and latent variable models to mother, father, and teacher ratings of ADHD inattention symptoms, sluggish cognitive tempo, and depressive symptoms in a sample of 2,142 Spanish children (age range 8–13 years;
M = 10.30,
SD = 1.21). Most interestingly, across all three sources, the same two ADHD inattention symptoms
difficulty keeping attention focused during tasks and
avoids, dislikes or is reluctant to engage in tasks that require sustained mental efforts showed unique relations with academic impairment. To summarize, each of these network studies uncovered important aspects of psychopathology, including the mutual associations among symptoms and the centrality of symptoms in a mental disorder network. However, the important role of FI has rarely been considered. To our knowledge, no study to date has identified which individual ADHD, ODD, CD, and CU symptoms show the strongest associations with particular domains of FI in a clinical sample of school-age children, in whom the associations between symptoms and impairments are probably more pronounced and relevant than in a community sample (Borsboom,
2017).
The Present Study
The overall aim of this study was to enhance the understanding of how individual symptoms of ADHD and disruptive behavior disorders (i.e. ODD, CD, CU symptoms) may differentially relate to global FI and to FI in the five domains of psychological strain; home life and family members; relationships with adults; relationships with children and recreational activities; and academic performance. We extended previous research according to four important aspects: (a) We assessed FI domains specifically related to ADHD symptoms and, likewise, specifically related to ODD/CD/CU symptoms. (b) Consistent with current evidence, we included not only symptoms of ODD, but also affective dysregulation symptoms, as suggested in the ICD-11 for the subtype ODD with chronic irritability/anger (Evans et al.,
2017; World Health Organization,
2019). (c) We provided another rater perspective (i.e. clinician ratings), since structured clinical interviews may be considered as the gold standard for diagnosing mental disorders (Rettew et al.,
2009). (d) We extended previous findings by using a clinical sample of school-age children.
First, we determined the impact of individual ADHD symptoms or ODD/CD/CU symptoms, respectively, on global FI using linear regression, combined with relative importance analyses. In line with the results of previous studies, we assumed that the ADHD symptoms
leaves seat, blurts out,
interrupts, or
organizational skills (Goh et al.,
2021a,
b; Mota & Schachar,
2000; Zoromski et al.,
2015) and the ODD-related symptoms of irritability, such as
loses temper, touchy, or
angry (Dougherty et al.,
2013; Wesselhoeft et al.,
2019) would have the highest impact on global FI. Second, we estimated two psychological networks to identify the unique strongest associations between individual ADHD symptoms or ODD/CD/CU symptoms, respectively, and multiple FI domains. For the ADHD network, we expected that the symptoms most strongly associated with academic FI would originate from the inattention domain (Burns et al.,
2022; Garner et al.,
2013; Goh et al.,
2020; Massetti et al.,
2008; Willcutt et al.,
2012; Zoromski et al.,
2015), while symptoms most strongly associated with social impairment would originate from the hyperactivity-impulsivity domain (Garner et al.,
2013; Goh et al.,
2021a,
b; Willcutt et al.,
2012). For the ODD/CD/CU network, we expected the symptoms most strongly associated with academic FI to originate from the CD domain (Burke et al.,
2014), the symptoms most strongly associated with impaired home life and family members and with relationships with adults to originate from the ODD or CD domain (Dose et al.,
2019; Kernder et al.,
2019), and the symptoms most strongly associated with impaired relationships with children to originate from the ODD or CU domain (Burke et al.,
2014; Dose et al.,
2019; Haas et al.,
2018; Kernder et al.,
2019).