Types of Error

1/27/15 Patient Safety SBMR #3


The skills, rules and knowledge (SRK) classification scheme for human error was developed by Jens Rasmussen, a professor who studied system safety and human factors for many years[i]. SRK classification is based on three levels of cognitive processing that may be utilized when an individual encounters information.

Unlike the Swiss Cheese Model which emphasizes system failures, the contribution of human factors to error causality is the focus of the SRK classification. Purely systemic reforms, while essential, are not sufficient to prevent errors or breaches to patient safety because of the unique features of the healthcare industry[i]. One such distinction is the fact that healthcare is provided one-to-one, or by many individuals serving one patient versus other hazardous industries where a few individuals serve many end-users.

Acquisition of the mental skills necessary to detect and avoid a potentially dangerous situation, on the part of doctors will reduce the likelihood of error. This has been described as metacognition, or “thinking about thinking”[ii]. The three levels of cognitive processing and associated errors are described and illustrated with examples below[iii].

Three levels of cognitive processing and associated errors

1. Skill-based error:

Individuals who process information at the skill level are usually extremely experienced with the task. Information cues are processed at the subconscious level, instead of processing and then integrating the information to determine a course of action. For example, your acne cream is next to your toothbrush one morning; and you unwittingly put acne cream on your toothbrush! The errors associated with this are usually errors of execution where a person performs an automatic behavior associated with a different cue rather than the intended one.

Thus, a skill-based error results from an action chosen by an individual which is not in accordance with their intention(s).

2. Rule-based error:

Performance at the rule-based level implies some familiarity with the information, but insufficient experience to perform the task at a sub-conscious level. Information cues are interpreted and matched with previous experience to determine appropriate actions from stored rules in the memory.

Error results from failure to recognize a familiar pattern where a rule may be applied or noncompliance with an existing rule, such as those placed by a system. It can also occur from application of the wrong rule when a seemingly familiar situation is encountered. For instance, a 16 month old child brought to his PCP for the third time with reddish discoloration on wet diapers is sent home as having uric acid crystals, when he in fact has a rhabdomyosarcoma of the bladder!

3. Knowledge-based error

Intelligent problem solving is required when new situations are encountered, or when an individual does not have rules stored in memory for previously learned information. For example, the first time a person bakes cookies, they may use baking powder instead of baking soda since they think they are interchangeable ingredients. Knowledge-based errors result from deficiency in knowledge or the ability of an individual to apply existing knowledge to new information.

Strategies for avoiding each type of error

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Systemic efforts for patient safety still leave many frontline workers like nurses and junior doctors vulnerable to human error. As residents and fellows who represent the frontline of healthcare provision in academic hospitals, we need to increase our understanding of errors, and heighten our recognition of thought patterns that predispose to mistakes. Our education on Cognitive Bias is part of this. False assumptions and faulty thinking can lead to preventable adverse events. One way to promote collective learning about such false assumptions is to report and discuss breaches to patient safety, even when harm does not occur. Reports should be submitted through the iCare system at the University of Minnesota Masonic Children’s Hospital and other equivalent systems in the hospitals where we provide care.

For more information:

(v)Mattox, Elizabeth Andersson. "Strategies for improving patient safety: linking task type to error type." Critical care nurse 32.1 (2012): 52-78.

(ii)Reason, James. "Beyond the organisational accident: the need for “error wisdom” on the frontline." Quality and Safety in Health Care 13.suppl 2 (2004): ii28-ii33.

Reason, James. "Understanding adverse events: human factors." Quality in Health Care 4.2 (1995): 80-89.

Advanced material

Tallentire, Victoria R., et al. "Exploring error in team-based acute care scenarios: an observational study from the United Kingdom." Academic Medicine 87.6 (2012): 792-798.

(i)Rasmussen, Jens. "Skills, rules, and knowledge; signals, signs, and symbols, and other distinctions in human performance models." Systems, Man and Cybernetics, IEEE Transactions on 3 (1983): 257-266.

Human Error Types (Webpage) accessed at SKYbrary [http://www.skybrary.aero/index.php/Human_Error_Types]

(iii)Croskerry, Pat. "Cognitive forcing strategies in clinical decision-making." Annals of emergency medicine 41.1 (2003): 110-120.

(IV) WikiofScience: Error (Human Error) accessed at http://wikiofscience.wikidot.com/quasiscience:error#toc5 on January 12, 2015