Clinical reasoning is one of the central components of psychological assessment. The identification of a client's psychological difficulties and the subsequent depiction of their onset, development, and interrelationships enables clinicians to plan treatment in a systematic and effective manner. In an article (Ward, Vertue, & Haig, 1999), we outlined the abductive theory of method (ATOM) and argued that it offered a useful framework for highlighting and integrating the major phases of psychological assessment. These phases involve detecting clinical phenomena, postulating psychological mechanisms, developing a case formulation, and evaluating a case formulation. In this article we present a revised version of the adaptation of ATOM and elaborate on the related clinical dimensions of assessment.
