Re-examining the construct of impulsivity: implications fro depression in adults

[Truncated abstract] Background: Impulsivity and depression, on their own, represent two major problems in modern society. They co-occur in several psychiatric disorders and clinical syndromes. Yet, it is not clear whether, and how, the two conditions are related. Limited research in the field has been inconclusive, possibly due to the varied definitions and assessments of impulsivity used in different studies. Aims: This thesis seeks to (i) critically re-examine the impulsivity construct; (ii) examine the existing literature on impulsivity and depression; (iii) identify the conceptual and methodological shortcomings of current research on impulsivity and that on impulsivity and depression that may have impeded the understanding of the association between impulsivity and depression; (iv) address such shortcomings by developing a new measure of impulsivity; and thereby (v) advance the investigation into the possible relationship between impulsivity and depression. Methods & Results: Stage I: The thesis begins with a critical appraisal and synthesis of the literature on impulsivity, and proposes a working integrated framework for impulsivity. This framework consists of three formally recognized types of impulsivity: rapid response (acting without thinking), preference for immediate reinforcement (choosing an immediate, small reward over a delayed, larger reward), and risk underestimation (underestimating the likelihood of adverse consequences of a behaviour). Also according to this framework, these three independent types of impulsivity can be unified by two additional, implicit elements of impulsivity: impulsivity is a response to, or in the presence of, some challenge or conflict (the 'challenge' element); and impulsivity leads to consequences that misalign with the person’s initial goal or 'best interest' (the 'goal misalignment' element). This framework is then applied in a systematic review of the literature on impulsivity and depression. Stage II: A new measure for impulsivity (the Types of Impulsivity Scale, TIS) is developed, based on the working integrated framework, to address the limitations of the existing measures of impulsivity. The TIS is a scenario-based scale, with the scenarios based on daily life experiences. In its finally adopted version, the TIS contains 14 scenarios, with four questions in each scenario. The first question assesses the degree of salience or relevance of the scenario to the respondent. The remaining three questions assess the three theoretical types of impulsivity: rapid response, preference for immediate reinforcement, and risk underestimation, respectively...