The Swiss cheese model of safety incidents: are there holes in the metaphor?

Background: Reason's Swiss cheese model has become the dominant paradigm for analysing medical errors and patient safety incidents. The aim of this study was to determine if the components of the model are understood in the same way by quality and safety professionals. Methods: Survey of a volunteer sample of persons who claimed familiarity with the model, recruited at a conference on quality in health care, and on the internet through quality-related websites. The questionnaire proposed several interpretations of components of the Swiss cheese model: a) slice of cheese, b) hole, c) arrow, d) active error, e) how to make the system safer. Eleven interpretations were compatible with this author's interpretation of the model, 12 were not. Results: Eighty five respondents stated that they were very or quite familiar with the model. They gave on average 15.3 (SD 2.3, range 10 to 21) correct answers out of 23 (66.5%) - significantly more than 11.5 correct answers that would expected by chance ( p < 0.001). Respondents gave on average 2.4 correct answers regarding the slice of cheese ( out of 4), 2.7 correct answers about holes ( out of 5), 2.8 correct answers about the arrow ( out of 4), 3.3 correct answers about the active error ( out of 5), and 4.1 correct answers about improving safety ( out of 5). Conclusion: The interpretations of specific features of the Swiss cheese model varied considerably among quality and safety professionals. Reaching consensus about concepts of patient safety requires further work.