Evaluation is seen as key in any systematic attempt to improve decision making effectiveness in unstructured tasks. Decision Support Systems (DSS) are systems designed to extend a manager’s ability to deal with the complexity of the decision situation. It is argued that outcome-oriented evaluation (an evaluation that appears to dominate current organizational practices) limits the development of DDS. Process-based measures of decision making effectiveness are developed and analyzed using the concept of an evaluation space as an organizing framework. Both in theory and in practice, improving decision making effectiveness in unstructured tasks in a systematic fashion is found to be an elusive goal. Seeking a better understanding of decision making—by identifying relevant simplifying procedures, rules and beliefs; by defining an explicit reference group of effective decision makers; by developing a model of the decision task—should instead be an important operational objective in any effort to improve effectiveness.