The decisive moment: making diagnostics decisions and designing treatments

In this thesis psychologists’ diagnostic decision making processes and their relationship with treatment decisions were investigated. Theoretical diagnostic models prescribe that the diagnostic process consists of two decision processes: classification and case formulation (Witteman, Harries, Bekker, & Van Aarle, 2007). These diagnostic decisions are used to form an integrated client model on which psychologists base their treatment decisions (Haynes, 1993). However, in clinical practice, the complex and dynamic nature of the diagnostic tasks hampers an optimal performance (Gambrill, 2005). Thus far, it has remained unclear whether the prescribed diagnostic decisions are performed in clinical practice and determine treatment decisions. Two research questions were investigated in this thesis: 1) What characterizes the diagnostic decision making process in clinical practice? and 2) What is the role of the diagnostic decision making processes in designing treatments? In chapters 2 and 3 the type of diagnostic decisions considered in the diagnostic process (chapter 2) and the sequence of decisions (chapter 3) was explored using a questionnaire with a written case description. In chapter 4 the third study is described in which an authentic diagnostic task was used. The type and sequence of psychologists’ diagnostic decisions as well as their considerations were examined in a diagnostic interview with a simulated client. In addition, it was examined to what extent these considerations are connected to psychologists’ assessment reports based on their diagnostic interviews. In chapter 5 the influence of client case complexity on the quality of case formulations was investigated. In addition, we explored the relationship between psychologists’ diagnostic decisions (classification and case formulation), their theoretical orientations and the treatment decisions. In the final chapter, the main findings of all four studies are summarized and discussed, the concept of a decision support tool is described, and suggestions for further research are made. The studies in this thesis show that psychologists’ diagnostic processes are adaptive and characterized by a focus on the client’s complaints and symptoms and on treatment selection while they continuously shift between all diagnostic decisions and reconsider previous decisions. The decisions made in the diagnostic process contribute only slightly to treatment design.