Diagnostic operationalization and phenomenological heterogeneity in psychiatry: The case of attention deficit hyperactivity disorder

Abstract

Introduction. We assessed the impact of polythetic conceptualizations of mental disorders on the validity and reliability of psychiatric diagnosis, with a specific focus on two levels of heterogeneity: phenomenological and pathophysiological. Objective. We investigated this issue using attention deficit hyperactivity disorder (ADHD) as an example. Method. We examined individuals from two samples enriched for psychopathology (n = 1 255 children in Porto Alegre and 1 257 children in São Paulo, Brazil). We conducted a series of data analyses to investigate phenomenological heterogeneity, including confirmatory factor analysis. We also investigated pathophysiological heterogeneity using symptom-level regressions between ADHD symptoms and four neurocognitive processes consistently linked to ADHD (working memory, inhibitory control, intra-subject variability in reaction times, and temporal processing). Lastly, we assessed the performance of polythetic systems for reliability testing inter-rater and test-rest reliability of two well-known symptomatic scales. Results. Among the 116 200 possible combinations of symptoms to achieve DSM symptomatic threshold for categorical ADHD diagnosis, we found 173 combinations in the two independent samples, and only four were replicated in both samples (2.3%). We also found that the number of ADHD symptoms is a poor indicator of variation in the general ADHD latent trait. Overall, symptoms did not have specific profiles of associations with any of the neurocognitive processes. Reliability analyses revealed that increasing the number of items augments overall reliability of measurements. Discussion and conclusion. Our findings illustrate both potential benefits and problems inherent to the polythetic system for ADHD. Implications for the search of mechanisms underlying psychiatric disorders are discussed.