Common Factors and Interpretation of the p Factor of Psychopathology

One of the most discussed recent topics in psychopathology research is the p factor of mental illness. This single dimension is understood to measure "a person's liability to mental disorder, comorbidity among disorders, persistence of disorders over time, and severity of symptoms."¹ A recent paper by Constantinou et al.² published in the Journal investigated the external validity of the p factor. We commend the authors for the contribution to the literature and want to highlight two points: (1) the interpretation of p as a causal entity, and (2) selection of bifactor models over alternative models for reasons of superior fit.