“shocking conclusion. It suggested that there appears to be one common pathway to all mental illnesses. Caspi and Moffitt called it the p-factor, in which the p stands for general psychopathology. They argued that this factor appears to predict a person’s liability to develop a mental disorder, to have more than one disorder, to have a chronic disorder, and it can even predict the severity of symptoms. This p-factor is common to hundreds of different psychiatric symptoms and every psychiatric diagnosis. Subsequent research using different sets of people and different methods confirmed the existence of this p-factor.25 However, this research was not designed to tell us what the p-factor is. It only suggests that it exists—that there is an unidentified variable that plays a role in all mental disorders.”