Why psychopathology research should avoid studying one mental disorder at a time: An intergenerational and developmental evidence base for understanding "p".

Most etiological research on mental disorders tries to find specific causes of specific disorders. However, the search for causal specificity has been elusive. In fact, new evidence reveals that the major etiological factors are transdiagnostic. One possible reason for why the search for specificity has been elusive is that most disorders are more similar than they are distinct, an idea that prompted research on "p"-the tendency of a person to develop a wide range of different mental disorders. Here we bring together data from unique sources to provide the intergenerational and developmental empirical evidence base for understanding "p." Men and women with a history of mental disorders tend to mate with partners who are also prone to have mental disorders, but not necessarily the same disorders. This creates a situation whereby their offspring, whether through genetic and/or environmental transmission, are at heightened risk of developing a variety of different mental disorders, but which specific disorder offspring ultimately develop is not easy to predict. Given that offspring inherit these multiple liabilities, it may not surprise that these liabilities manifest as different disorders at different points throughout their lives, but which disorder emerges at a particular time is difficult to foretell. The intergenerational and developmental evidence about the familiality and course of mental disorders helps to deconstruct "p" and invites psychopathology research and clinical science to reconsider their common approach to studying one mental disorder at a time. (PsycInfo Database Record (c) 2026 APA, all rights reserved).