Patient safety has only recently been subjected to wide-spread systematic study. Healthcare differs from other high risk industries in being more diverse and multi-contextual, and less certain and regulated. Also many patient safety problems are low-frequency events associated with many, varied contributing factors. The subject of this paper is the epistemology of patient safety (the science of the method of finding out about patient safety). Patient safety research is considered here on the background of a risk management framework which requires (...) researchers to: • Understand the context - as a subset of healthcare quality, services and systems research, with technical and human behavioural (cultural) components and a range of external and internal organisational influences, a wide range of research disciplines is necessary • Identify the risks - identify the things that go wrong and the frequency and nature of different types of incidents from sources such as medical record review, observational studies, audit, incident and medico-legal reports • Analyse the risks - deconstruct the things that go wrong, identifying contributing factors and trying to detect trends and patterns in contributing factors, detection, mitigation factors, ameliorating factors and actions taken to reduce risk • Evaluate the risks - decide on priorities, identifying preventive and corrective strategies and judging the risk- and cost-benefit of potential corrective strategies such as standardisation or simplification of a process or device • Manage the risk - evaluate and scope preventive and/or corrective strategies and then implement these, or place the problem on a risk register pending solution, or accept that what is needed is unaffordable • Communicate and consult - use interactive sessions, audit, on-going feedback, reminders and patient mediated prompts • Monitor and review the state of the problem - get baseline trends and patterns so that changes can be tracked and properly attributed to an intervention A hierarchy of levels of evidence has been proposed for clinical research and we argue that insufficient weighting has been given to lower ranked levels of research and to qualitative research, although critical interpretive synthesis is now gaining acceptance in mainstream thinking (e.g. by the Cochrane Collaboration). Fundamental challenges remain including how to grasp the elusive concept of patient safety, how to quantify, characterise and cost the problems, how to judge the extent to which harm can be attributed to errors, violations or system failures, how to identify contributing factors and the extent to which they can be implicated, how to judge whether incidents or their precursors are preventable, how to generate strong evidence to make healthcare safer and how to translate research into practice. Future directions include addressing the mundane as well as rare, dramatic events, and developing further research in non-hospital settings and in developing countries. In summary, a mixture of qualitative and quantitative methods, using information from all available data sources and combining retrospective, real time and prospective study designs, is necessary to address some of the more difficult patient safety problems. (shrink)