Concerns about the safety and quality of health care have created the 'patient safety movement' and led to a wide variety of activity. Although many may not have realized it, there is a great debate about the best strategy for effecting improvement that carries over into debates about the quality of 'evidence' and what constitutes scientific activity. This debate is rooted in underlying and often unrecognized differences in the philosophies of science and additionally is divided along social and professional lines, with healthcare researchers tending to assuming one side, and human factors professionals taking the other. We will explore these competing approaches, using the problems associated with handoffs in clinical work as an exemplar.