Antisocial behavior, substance use, and impulsive and aggressive personality traits often co-occur, forming a coherent spectrum of personality and psychopathology. In the current research, the authors developed a novel quantitative model of this spectrum. Over 3 waves of iterative data collection, 1,787 adult participants selected to represent a range across the externalizing spectrum provided extensive data about specific externalizing behaviors. Statistical methods such as item response theory and semiparametric factor analysis were used to model these data. The model and assessment instrument that emerged from the research shows how externalizing phenomena are organized hierarchically and cover a wide range of individual differences. The authors discuss the utility of this model for framing research on the correlates and the etiology of externalizing phenomena. Keywords drug; alcohol; impulsivity; aggression; classificationThe existence of individual differences in the tendency to contain versus express impulses has been recognized in academic psychology since its inception as a discipline (James, 1890(James, /1983. In more recent times, this domain has been instantiated in psychological constructs ranging from disinhibition (Clark & Watson, 1999;Gorenstein & Newman, 1980) to impulsivity (Barratt, 1994;Dickman, 1990;Gray, 1981;Whiteside & Lynam, 2001), ego control (J. Block, 1965; J. H. Block & Block, 1980), constraint (Tellegen, 1985), the problem behavior syndrome (Jessor & Jessor, 1977), sensation seeking (Zuckerman & Kuhlman, 2000), and novelty seeking (Cloninger, Svrakic, & Przybeck, 1993). In addition, a dimension of effortful control is a salient feature of childhood temperament that likely relates to these disinhibitory personality characteristics in adulthood (Rothbart, Ahadi, & Evans, 2000). Robust correlations have also been observed between these disinhibitory personality constructs and mental disorders involving substance problems and antisocial behavior (for a review, see Sher & Trull, 1994).In spite of these rich interrelations, many of these constructs continue to be studied and conceptualized as separate entities, in separate literatures. A major reason for this fragmentation is the lack of an integrative model of this domain (Widiger & Clark, 2000). The purpose of the current research is to further the development of an empirically based model of NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript this broad domain of personality and psychopathology, which we term the externalizing spectrum (Krueger, Markon, Patrick, & Iacono, 2005). Origins of the Externalizing Spectrum ConceptualizationAs applied to adult psychopathology, the externalizing spectrum conceptualization emerged initially from research on mental disorders defined within current nosologies. In the Diagnostic and Statistical Manual of Mental Disorders (4th ed., text. rev.; DSM-IV-TR; American Psychiatric Association, 2000), various forms of substance problems are conceptualized as discrete disorder...

A crucial challenge in efforts to link psychological disorders to neural systems, with the aim of developing biologically informed conceptions of such disorders, is the problem of method variance (Campbell & Fiske, 1959). Since even measures of the same construct in differing domains correlate only moderately, it is unsurprising that large sample studies of diagnostic biomarkers yield only modest associations. To address this challenge, a construct-network approach is proposed in which psychometric operationalizations of key neurobehavioral constructs serve as anchors for identifying neural indicators of psychopathology-relevant dispositions, and as vehicles for bridging between domains of clinical problems and neurophysiology. An empirical illustration is provided for the construct of inhibition-disinhibition, which is of central relevance to problems entailing deficient impulse control. Findings demonstrate that: (1) a well-designed psychometric index of trait disinhibition effectively predicts externalizing problems of multiple types, (2) this psychometric measure of disinhibition shows reliable brain response correlates, and (3) psychometric and brain-response indicators can be combined to form a joint psychoneurometric factor that predicts effectively across clinical and physiological domains. As a methodology for bridging between clinical problems and neural systems, the construct-network approach provides a concrete means by which existing conceptions of psychological disorders can accommodate and be reshaped by neurobiological insights.

The Externalizing Spectrum Inventory (ESI; Krueger, Markon, Patrick, Benning, & Kramer, 2007) provides for integrated, hierarchical assessment of a broad range of problem behaviors and traits in the domain of deficient impulse control. The ESI assesses traits and problems in this domain through 23 lower-order facet scales organized around three higher-order dimensions, reflecting general disinhibition, callous-aggression, and substance abuse. The full-form ESI contains 415 items, and a shorter form would be useful for questionnaire screening studies or multi-domain research protocols. The current work employed item response theory and structural modeling methods to create a 160-item brief form (ESI-bf) that provides for efficient measurement of the ESI’s lower-order facets and quantification of its higher-order dimensions either as scale-based factors or as item-based composites. The ESI-bf is recommended for use in research on psychological or neurobiological correlates of problems such as risk-taking, delinquency, aggression, and substance abuse, and studies of general and specific mechanisms that give rise to problems of these kinds.

Using data from over 1,000 male and female twins participating in the Minnesota Twin Family Study, the authors examined developmental change, gender differences, and genetic and environmental contributions to the symptom levels of four externalizing disorders (adult antisocial behavior, alcohol dependence, nicotine dependence, and drug dependence) from ages 17 to 24. Both men and women increased in symptoms for each externalizing disorder, with men increasing at a greater rate than women, such that a modest gender gap at age 17 widened to a large one at age 24. Additionally, a mean-level gender difference on a latent Externalizing factor could account for the mean-level gender differences for the individual disorders. Biometric analyses revealed increasing genetic variation and heritability for men but a trend toward decreasing genetic variation and increasing environmental effects for women. Results illustrate the importance of gender and developmental context for symptom expression and the utility of structural models to integrate general trends and disorder-specific characteristics.

The findings have implications for proposals to reconceptualize psychopathology in neurobiological terms.