Understanding Irritability: Definition Measurement and Modelling

Abstract

Irritability is common to our day-to-day experiences and as a transdiagnostic phenomenon in psychiatric disorders, and yet it is ill-defined and poorly understood. Its ubiquity means that it is impossible to capture in its entirety, and therefore this thesis approaches the characterisation of irritability by measuring and modelling the phenomenon at key junctures where it is most likely to occur in order to capture its essence. Therefore, the overarching aim of this thesis is to further our understanding of irritability by sampling the phenomenon widely beginning in health and moving through to illness. To inform this inquiry the thesis begins with a careful analysis of the concept of irritability. This then allows the examination of the phenomenon at key transitions and intersections that are inherently rich in irritability such as adolescence and mood disorders. By examining a population of healthy adolescents, and a corresponding population of adolescents and adults who have mood disorders, this thesis finds that irritability is linked to the development of psychopathology in adolescents, and that this may serve as an indicator of bipolarity. Based on these findings, this thesis proposes a novel model of irritability that incorporates age, gender and mood. These findings, and the novel model they underpin, serve as a foundation upon which further research can be conducted systematically to characterise and better understand this hitherto elusive phenomenon.