What Causes Errors

Swiss Cheese Model

Quality Improvement/Patient Safety SBMR

Tuesday, Jan. 26th, 7:30-8am

UMMCH 6th floor conference room

All Pediatric residents and fellows are encouraged to attend!

Morning report calendar can be found here:



Error is a failure to carry out a planned action as intended or application of an incorrect plan[i]. Errors in medical practice may occur either in the process of planning for a patient’s care or when the plan of care is being implemented.

Swiss Cheese Model

The Swiss Cheese Model helps us to understand how errors in patient care result in circumstances or agents that have the potential to cause harm to a patient[ii]. The Swiss Cheese Model was developed in 1990 by James Reason, a professor of psychology to explain how error results in harm to a patient when latent organizational factors interact with human factors to allow, rather than prevent error from slipping through[iii]. The Swiss cheese analogy demonstrates how hazards are prevented in a complex system like healthcare by a series of barriers, defenses and safeguards. However, each barrier has weaknesses or holes similar to Swiss cheese. So, if the holes in the different barriers randomly align, an error passes through and becomes hazardous to a patient. No single individual error is sufficient to cause an accident in a medical setting. The majority of medical errors are caused by faulty systems, processes and conditions that lead people to make mistakes or fail to prevent them.
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2 types of failures

The Joint Commission categorizes error using two main groups: system failures are not within the direct control of the clinician, and human failures usually involve direct contact between the clinican and patient[iv]. Examples of system failure include inadequate staff orientation, limited access to information or understaffing medical staff for a high census. Such errors in the design, organization training, or maintenance are system failures that may contribute to human failure. Human failures can be knowledge-based, skill-based, rule-based or unclassifiable when the focus is on the practitioner.


The Swiss Cheese Model acts as a lens for evaluating medical errors that places emphasis on the health care system, instead of blaming individuals for an error that reaches a patient. It also acknowledges the weaknesses within each preventive barrier and how these weaknesses can align to have breaches in patient safety.

For more information:

· Reason, James. "Human error: models and management." Bmj 320.7237 (2000): 768-770.

· Perneger, Thomas V. "The Swiss cheese model of safety incidents: are there holes in the metaphor?." BMC health services research 5.1 (2005): 71.

· Jeffs, Lianne, et al. "Learning from near misses: from quick fixes to closing off the Swiss-cheese holes." BMJ quality & safety (2012): bmjqs-2011.

· Li Y, Thumbleby J. "Hot cheese: a processed Swiss cheese model." JR Coll Physicians Edinb44 (2014): 116-21. [This is a critique of SCM, proposing a modification called Hot Cheese Model J]

Advanced material:

· Kohn LT, Corrigan JM, Donaldson MS, eds. To Err Is Human: Building a Safer Health System. Washington, DC: National Academy Press; 1999:1.

· Warrick, Catherine, et al. "Diagnostic error in children presenting with acute medical illness to a community hospital." International Journal for Quality in Health Care 26.5 (2014): 538-546. [Application of SCM in a UK community hospital]

· Veazie, Peter J. "An individual-based framework for the study of medical error."International Journal for Quality in Health Care 18.4 (2006): 314-319.

· Moloney, J. "Error modelling in anaesthesia: slices of Swiss cheese or shavings of Parmesan." British journal of anaesthesia (2014): aeu223.

· Vioque, Sandra M., et al. "Classifying errors in preventable and potentially preventable trauma deaths: a 9-year review using the Joint Commission's standardized methodology."The American Journal of Surgery (2014).

· This article applied the SCM to analysis in an adult patient: Offredy, Maxine, Martin Rhodes, and Yvonne Doyle. "The anatomy, physiology and pathogenesis of a significant untoward incident." Quality in primary care 17.6 (2009): 415-421.

· Reinertsen, James L. "Let's talk about error." Bmj 320.7237 (2000): 730.

Online course:

IHI Open School Academy Patient Safety 100: Introduction to Patient Safety.

www.ihi.org, go to IHI Open School under the education tab

**Free to trainees**

[i] Runciman, William, et al. "Towards an International Classification for Patient Safety: key concepts and terms." International Journal for Quality in Health Care 21.1 (2009): 18-26.

[ii] Reason, James. "Human error: models and management." Bmj 320.7237 (2000): 768-770.

[iii] Moloney, J. "Error modelling in anaesthesia: slices of Swiss cheese or shavings of Parmesan." British journal of anaesthesia (2014): aeu223.

[iv] Chang, Andrew, et al. "The JCAHO patient safety event taxonomy: a standardized terminology and classification schema for near misses and adverse events." International Journal for Quality in Health Care 17.2 (2005): 95-105.