BEHAVIOUR CHANGE Vol. 16, No. 1 1999 pp. 49–63 49 I n a recent paper (Ward & Haig, 1997), we argued that there are parallels between scien- tific method and psychological assessment. The scientist frequently employs methods to detect empirical phenomena, and also seeks to explain the occurrence of those phenomena by con- structing models or theories of the causal mech- anisms thought to be responsible for their occurrence. Similarly, in psychological assess- ment, clinicians characteristically attempt to systematically collect data that enable them to identify a client’s difficulties and their causes (Shapiro, 1979). The result of this process is a conceptual model representing the client’s vari- ous complaints, their causes, and their interrela- tionships. The process of psychological assessment can be construed, in part, as system- atic inquiry into a client’s problems, which is guided by scientific method. In this paper, we present a general theory of scientific method and show how it can illumi- nate the basic idea that psychological assess- ment is a form of systematic scientific inquiry. Our basic contention is that this general method can provide clinicians with a conceptual frame- work for identifying and structuring their vari- ous basic assessment tasks. We use the term clinical assessment in a broad sense to cover the various assessment phases that range from phenomena detection through to evaluation of the case formulation. It is important to note that this account of scientific method can be used by clinicians of varying theoretical orientations. The method provides a plan of inquiry that guides the thera- pist, both in the gathering of clinically pertinent information and its subsequent integration in a psychological formulation. In this regard, the therapist’s theoretical orientation could be cog- nitive-behavioural, some other form of behavioural therapy, and so on. According to our theory of method, what matters is that the Abductive Method and Clinical Assessment in Practice Tony Ward University of Melbourne Frances M. Vertue and Brian D. Haig University of Canterbury Clinical reasoning is one of the central components of psychological assessment. The identifi- cation of a client’s psychological difficulties and the subsequent depiction of their onset, devel- opment, and interrelationships enables clinicians to plan treatment in a systematic and effective manner. In a recent paper (Ward & Haig, 1997), we presented an abductive theory of method and showed how it offered a useful framework for highlighting and integrating the major phases of psychological assessment. These phases involve detecting clinical phenomena, pos- tulating psychological mechanisms, developing a case formulation, and evaluating a case for- mulation. In this paper we outline the abductive theory and elaborate on the related clinical dimensions of assessment, while illustrating them with an ongoing case example. Address for correspondence: Dr Tony Ward, Department of Criminology, University of Melbourne, Parkville VIC 3052, Australia or Dr Brian Haig, Department of Psychology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. E-mail: t.ward@criminology.unimelb.edu.au or b.haig@psyc.canterbury.ac.nz