Research and clinical investigations in psychiatry largely rely on the de facto assumption that the diagnostic categories identified in the Diagnostic and Statistical Manual (DSM) represent homogeneous syndromes. However, the mechanistic heterogeneity that potentially underlies the existing classification scheme might limit discovery of etiology for most developmental psychiatric disorders. Another, perhaps less palpable, reality may also be interfering with progress—heterogeneity in typically developing populations. In this report we attempt to clarify neuropsychological heterogeneity in a large dataset of typically developing youth and youth with attention deficit/hyperactivity disorder (ADHD), using graph theory and community detection. We sought to determine whether data-driven neuropsychological subtypes could be discerned in children with and without the disorder. Because individual classification is the sine qua non for eventual clinical translation, we also apply support vector machine-based multivariate pattern analysis to identify how well ADHD status in individual children can be identified as defined by the community detection delineated subtypes. The analysis yielded several unique, but similar subtypes across both populations. Just as importantly, comparing typically developing children with ADHD children within each of these distinct subgroups increased diagnostic accuracy. Two important principles were identified that have the potential to advance our understanding of typical development and developmental neuropsychiatric disorders. The first tenet suggests that typically developing children can be classified into distinct neuropsychological subgroups with high precision. The second tenet proposes that some of the heterogeneity in individuals with ADHD might be “nested” in this normal variation.
The paper is: D. A. Fair, D. Bathula, M. A. Nikolas, J. T. Nigg. "Distinct neuropsychological subgroups in typically developing youth inform heterogeneity in children with ADHD." Proceedings of the National Academy of Sciences, 2012; DOI: 10.1073/pnas.1115365109
The study broke the control group into four different psychological clusters based on the outcome of half a dozen psychological tests ("The testing focused on memory, inhibition, attention, comprehension, and several other categories."), and then broke the ADHD subjects into four analogous clusters to those in the control group although two of the four clusters in the ADHD subjects had two subclusters each. The ADHD diagnosis that this cluster system was compared to was a two subtype (predominantly inattentive and combined type), rather than a three subtype system.
The glorified press release story at Science Daily makes the rather unappetizing and largely uninformative comparison of ADHD subtypes and cancer subtypes, but also explains a bit more how the study was conducted.