Progress in achieving quantitative classification of psychopathology

Abstract

Shortcomings of approaches to classifying psychopathology based on expert consensus have given rise to contemporary efforts to classify psychopathology quantitatively. In this paper, we review progress in achieving a quantitative and empirical classification of psychopathology. A substantial empirical literature indicates that psychopathology is generally more dimensional than categorical. When the discreteness versus continuity of psychopathology is treated as a research question, as opposed to being decided as a matter of tradition, the evidence clearly supports the hypothesis of continuity. In addition, a related body of literature shows how psychopathology dimensions can be arranged in a hierarchy, ranging from very broad "spectrum level" dimensions, to specific and narrow clusters of symptoms. In this way, a quantitative approach solves the "problem of comorbidity" by explicitly modeling patterns of co-occurrence among signs and symptoms within a detailed and variegated hierarchy of dimensional concepts with direct clinical utility. Indeed, extensive evidence pertaining to the dimensional and hierarchical structure of psychopathology has led to the formation of the Hierarchical Taxonomy of Psychopathology (HiTOP) Consortium. This is a group of 70 investigators working together to study empirical classification of psychopathology. In this paper, we describe the aims and current foci of the HiTOP Consortium. These aims pertain to continued research on the empirical organization of psychopathology; the connection between personality and psychopathology; the utility of empirically based psychopathology constructs in both research and the clinic; and the development of novel and comprehensive models and corresponding assessment instruments for psychopathology constructs derived from an empirical approach.

Keywords: DSM; Hierarchical Taxonomy of Psychopathology; ICD; Psychopathology; RDoC; classification; clinical utility; dimensions; mental disorder; nosology; personality.

Figure 1

Illustration of hypothetical data compatible with fully continuous and partially discrete models of psychopathological variation. In Panel A, the data points are generally well captured by positing a single group, in which Factor 1 and Factor 2 are positively correlated. In Panel B, the data are better captured by positing two groups, one in which Factor 1 and Factor 2 are positively correlated (the circles), and a second smaller group in which Factor 1 and Factor 2 are weakly negatively correlated (the triangles).

Figure 2

Illustration of an empirically based model of the internalizing spectrum. Constructs higher in the figure are broader and more general, whereas constructs lower in the figure are narrower and more specific (adapted from Waszczuk et al38). PTSD – post‐traumatic stress disorder, Social anx – social anxiety, OCD – obsessive‐compulsive disorder, GAD – generalized anxiety disorder, Cog depress – cognitive depression, Psychol panic – psychological panic, Euphoric activ – euphoric activation, Hyperactive cog – hyperactive cognition, Reckless overcon – reckless overconfidence.

Figure 3

Working Hierarchical Taxonomy of Psychopathology (HiTOP) consortium model. Constructs higher in the figure are broader and more general, whereas constructs lower in the figure are narrower and more specific (adapted from Kotov et al43). SAD – separation anxiety disorder, OCD – obsessive‐compulsive disorder, MDD – major depressive disorder, GAD – generalized anxiety disorder, PTSD – post‐traumatic stress disorder, PD – personality disorder, ODD – oppositional defiant disorder, ADHD – attention‐deficit/hyperactivity disorder, IED – intermittent explosive disorder.