Annual Research Review: Categories versus dimensions in the classification and conceptualisation of child and adolescent mental disorders – implications of recent empirical study

Abstract

The question of whether child and adolescent mental disorders are best classified using dimensional or categorical approaches is a contentious one that has equally profound implications for clinical practice and scientific enquiry. Here, we explore this issue in the context of the forth coming publication of the DSM-5 and ICD-11 approaches to classification and diagnosis and in the light of recent empirical studies. First, we provide an overview of current category-based systems and dimensional alternatives. Second, we distinguish the various strands of meaning and levels of analysis implied when we talk about categories and dimensions of mental disorder--distinguishing practical clinical necessity, formal diagnostic systems, meta-theoretical beliefs and empirical reality. Third, we introduce the different statistical techniques developed to identify disorder dimensions and categories in childhood populations and to test between categorical and dimensional models. Fourth, we summarise the empirical evidence from recent taxometric studies in favour of the 'taxonomic hypothesis' that mental disorder categories reflect discrete entities with putative specific causes. Finally, we explore the implications of these findings for clinical practice and science.

Mechanisms underpinning inattention and hyperactivity: neurocognitive support for ADHD dimensionality

“…A categorical view proposes that ADHD differs qualitatively from variation in the normal range, with the discontinuity in underlying risk processes around the diagnostic boundary. The dimensional view, by contrast, sees ADHD differing from normality only in degree, with a spectrum of severity expressing continuity in risk-disorder relationships (Coghill & Sonuga-Barke, 2012). In the former, diagnostic thresholds are conceptualized to reflect 'natural' boundaries linked to underlying causes; in the latter, they reflect clinical and societal burden.…”

Angiogenic, neurotrophic, and inflammatory system SNPs moderate the association between birth weight and ADHD symptom severity

“…The strength of this association, however, varies across studies [Nigg, 2006] and is not always replicated [Cornforth et al, 2012]. Consistent with the dimensional nature of ADHD [Levy et al, 1997;Coghill and Sonuga-Barke, 2012], the association between lower birth weight and ADHD-related phenotypes is continuous and extends into the normal birth weight range [Boulet et al, 2009;Phua et al, 2012;Qiu et al, 2012;Walhovd et al, 2012]. Lower birth weight is also associated with reduced anterior cingulate cortex, caudate nucleus, and total brain volumes [Peterson et al, 2003;Tolsa et al, 2004;de Kieviet et al, 2012;Walhovd et al, 2012], which are linked with ADHD behavioral symptomatology [Frodl and Skokauskas, 2012;Hart et al, 2013].…”

Pediatric anxiety disorders: from neuroscience to evidence-based clinical practice

“…As such, anxiety disorders would represent a variation in degree but not in kind. 99 This would imply a view of normal and pathological anxiety as falling along a dimension, with diagnostic thresholds reflecting clinical and societal burden rather than discontinuous pathophysiological states. If this view of anxiety is correct, it would be quite important to study the normal development of fears and learn to recognize temperaments that are closely related to psychopathology in infants.…”