Attention Deficit Hyperactivity Disorder (ADHD) is a prevalent psychiatric disorder (1-3). Although it is commonly conceptualized as a neurodevelopmental condition, it also includes features that resemble basic personality traits, such as neuroticism and impulsivity (4,5). Similar to broad personality traits, ADHD tends to co-occur with a wide range of other disorders, including mood disorders, anxiety disorders, personality disorders and substance disorders (6-9). Moreover, deficits in personality traits such as emotion-regulation, distractibility, irresponsibility, risk-taking and impulsivity are thought to be at the core of ADHD symptoms (10,11).
Most research on personality and psychopathology organizes individual differences in the form of the Five Factor Model (4), which includes the traits Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness. Notably, there are several variants of this model, including the Research Domain Criteria (RDoC) (12); the Hierarchical Taxonomy of Psychopathology (HiTOP) (13); the Alternative Model of Personality Disorder (AMPD) (14); and the ICD-11 proposal for personality disorder (15). All of them have in common the proposal that a few broad traits underlie functioning in a wide range of areas, including dysfunction related to inattention and hyperactivity. Associations between personality and psychopathology are particularly strong when maladaptive trait measures, or instruments that focus on personality-related problems, are used (16).
Several previous reviews have documented associations between FFM personality traits and ADHD (17-20). These reviews indicate that ADHD as a unified construct is most consistently related to low Conscientiousness, low Agreeableness, and high Neuroticism. This research also suggests that the sub-presentations of inattention and hyperactivity/impulsivity correlate differentially with personality traits which deviates from single construct ADHD (21,22). Specifically, Inattention is positively correlated to Neuroticism and negatively to Conscientiousness; and Hyperactivity/Impulsivity relates negatively to Agreeableness and positively to Extraversion (23). However, these results have not been summarized quantitatively. The goal of the present study was to use meta-analysis to summarize associations between adult ADHD and maladaptive personality traits.
The Five-Factor Model of Personality
The five-factor model of personality (FFM) consists of the following five factors: Neuroticism which refers to the extent of negative emotions, i.e. sadness, fear, hostility, and emotional lability that the individual experiences (24). Individuals high in this domain may be at risk for many different psychiatric and physical disorders, high comorbidity, lower quality of life, shorter lifespan and more extensive use of health care (25). Extraversion concerns how outgoing or talkative the individual is in most situations. Core traits are sociability, assertiveness, positive affect, and activity level (24). Low Extraversion, or introversion, may include social withdrawal, social detachment, intimacy avoidance, restricted affectivity and anhedonia (26-28) and extremely high Extraversion may represent personality pathology in sexual promiscuity, emotional intrusiveness, excessive self-disclosure and thrill-seeking behavior (29). Openness to experience describes the depth and breadth of an individual’s intellectual, artistic, and experiential life, with key facets such as aesthetic sensitivity, intellectual interests, and imagination (24). Although open individuals generally tend to have greater psychological well-being, maladaptive Openness can be found in distinguishing between major depression and bipolar disorder as well as different variants of schizotypy (30). Agreeableness concerns the extent of the individual’s motivation for prosocial behavior and pleasant interpersonal relationships. Important traits are compassion, trust, and politeness (24). Individuals low in Agreeableness tend to be critical, skeptical, try to push limits, express hostility and being condescending (30) . Agreeableness is also inversely linked to psychopathy and aggressive behavior (31,32). Maladaptive variants of extreme Agreeableness can result in gullibility, submissiveness, clinging, subservience, servility etc. (30). Conscientiousness refers to the individual’s level of organization, ability to complete tasks, and persistence in achieving long-term goals. Key concepts are orderliness, self-discipline, and reliability (24). However, both high and low Conscientiousness is associated with decreased functioning. Low Conscientiousness is characterized by disinhibition, irresponsibility, negligence, and rashness (33,34); and inflexible high Conscientiousness can result in perfectionism, fastidiousness, punctiliousness, workaholism and other facets of compulsivity (35-37).
The Integrated Five-Factor Model
Research has shown that multiple models of both normal-range and maladaptive personality traits can be integrated into the structure of the FFM (38-40). For instance, the trait Neuroticism is empirically and conceptually similar to the trait Negative Affectivity in the AMPD and ICD-11, Emotion Dysregulation in Livesley’s Dimensional Assessment of Personality Pathology (DAPP; (41), and the traits Harm Avoidance and (low) Self-Transcendence in Cloninger’s Temperament and Character Inventory (TCI; (42). Similarly, FFM Conscientiousness is similar to Disinhibition in the AMPD/ICD-11, Compulsivity on the DAPP-BQ, and low Novelty Seeking and Persistence on the TCI. For the purposes of this paper, labels that integrate normal-range and maladaptive aspects of the FFM (Markon et al., 2005; (39): Negative Emotionality, Positive Emotionality, Openness, Conscientious Inhibition, and Agreeable Inhibition (see table 1), were used.
Conceptualizing ADHD within an Integrative Individual Differences Framework
Conceptualizing ADHD as a dimension or set of dimensions that can be placed within a general, evidence-based model of maladaptive personality traits has a number of potential clinical advantages (43-46). For instance, this model may help provide a principled and efficient means for conceptualizing heterogeneity in the presentation of individuals with ADHD diagnosis. Specifically, previous research suggests that Negative Emotionality and low Conscientious Inhibition are most strongly related to inattention, whereas Agreeable inhibition and Positive emotionality maybe more strongly related to hyperactivity and impulsivity (17,18,47,48). However, these relationships seem to be more complex with indications that hyperactivity is associated with higher levels of Positive emotionality and impulsivity with low Agreeableness. Evidence-based models of individual differences also help explain comorbidity, insofar as many disorders share underlying propensities for high Negative emotionality and low Conscientious and Agreeable Inhibition (49) these disorders should be expected to co-occur with inattentive and hyperactive symptoms. Identifying the underlying dimensions that support ADHD and its associated dysfunctions may also pave the way for more targeted treatments and research. As such, individual differences models such as the IFFM have the potential to improve the efficiency, validity, and utility of ADHD diagnoses.
However, there are certain challenges associated with placing adult ADHD in evidence-based personality models. First, a variety of measures of both ADHD and personality traits have been used in the past and there is no consensus in which measures to use and variation in measurement could impact patterns of association. In particular, stronger effects can be expected with maladaptive as opposed to normal range personality measures (16). There is also variability in the sense that both ADHD and the FFM traits can be conceptualized using lower order units – inattentive and hyperactive/impulsive subtypes in the case of ADHD and facets in the case of personality. The goal of this study was to provide a summary of the current evidence about how adult ADHD is related to IFFM personality traits. Given the existing body of research in adult populations, we focused on traits from the FFM, DAPP, HEXACO (50), and TCI. Given that relatively few studies have distinguished between ADHD subtypes, we also focused on ADHD as single construct.
In summary, the aim of this study was to quantify associations between ADHD and the traits of an Integrated FFM as represented by the FFM, DAPP, and TCI measurement systems, to better understand how ADHD fits into evidence-based models of personality and psychopathology, and ultimately enable improved clinical practice and research.