Glenn D. Walters, Elsa Ermer, Raymond A. Knight, Kent A. Kiehl

Although psychopathy has consistently been shown to distribute as a dimension, all prior studies have examined behavioral indicators that may be phenotypically distant from core biological correlates of the syndrome. The current studies attempted to determine whether biomarkers from a high-resolution structural MRI scan of selected limbic and paralimbic structures identified the latent structure of psychopathy as continuous. Participants were 254 adult male medium/maximum security inmates (Study 1) and 191 adolescent male maximum security inmates (Study 2) who volunteered to undergo research MRI scans. Indicators of gray matter concentration (GMC) in the adult sample and of gray matter volume (GMV) in the adolescent sample were subjected to taxometric analysis using three nonredundant taxometric procedures: mean above minus below a cut (MAMBAC), maximum covariance (MAXCOV), and latent-mode factor analysis (L-Mode). Evidence of continuous latent structure was found across samples (adults, adolescents), measures (GMV, GMC, Psychopathy Checklist-Revised [PCL-R], Psychopathy Checklist: Youth Version [PCL:YV]), and procedures (MAMBAC, MAXCOV, L-Mode). Continuous latent structure was also noted when biomarker (GMV, GMC) and behavioral (PCL) indicators were included in the same analysis. The current results support the view that psychopathy is a quantitative construct on which people differ in degree ("more of" or "less of") rather than a qualitative construct that assigns people to distinct categories ("either/or"). Continued development of the psychopathy construct may depend on our ability to identify, understand, and make effective use of its apparent continuous latent structure. (PsycINFO Database Record (c) 2014 APA, all rights reserved).