Use Error

Definition and delimitation

A use error describes a deviation between what a user does and what the manufacturer intended as correct operation, with the result that the use does not proceed as intended. The perspective is decisive here: A use error is not automatically attributed to the user as an individual failure but is understood in usability engineering primarily as a possible consequence of a user interface that is not optimally designed. This view is a basic principle of usability engineering: If an operating action repeatedly leads to errors, the cause often lies in the design of the user interface and not in a lack of care on the part of the user. User characteristics, task and use environment can also contribute. IEC 62366-1 therefore deliberately speaks of use error and not of user error.

Typical examples of use errors are confusing similar-looking controls, overlooking a warning message, a misinterpreted display, the inadvertent activation of a function or a programming error when entering therapy parameters. Perception and cognition errors are regarded in IEC 62366-1 as causes or contributing factors of use errors. The actual use error arises only through the resulting erroneous action or omission. The perception-cognition-action model helps to classify these causes.

Use error vs. abnormal use

In practice, the use error is often confused with abnormal use. The distinction is, however, relevant from a regulatory perspective. While a use error arises from a comprehensible, plausible misinterpretation or an ergonomically unfavorable design, abnormal use denotes deliberate action against the rules, for example intentionally bypassing safety mechanisms or grossly negligent misuse of the product.

This distinction largely determines whether a manufacturer has to react: For foreseeable use errors, it is obliged to reduce the risk, and primarily through design: first through inherently safe design, then through protective measures and only lastly through information for safety (ISO 14971). Abnormal use, by contrast, lies in principle outside its immediate area of responsibility, even though well-designed products should have a preventive effect here as well.

Use errors in the use-related risk analysis

Use errors are at the center of the use-related risk analysis (URRA). For each user task identified in the task analysis, it is examined systematically which use errors can occur, whether they can lead to a hazard-related use scenario and how high the resulting risk is for the patient, user or third parties. The identification of a use error serves not only to describe the risk but above all to derive suitable risk control measures.

Particularly important here are the tasks that the FDA calls critical tasks: tasks in which a use error can lead to serious harm, regardless of whether countermeasures are already in place. IEC 62366-1 does not know this term and works instead with hazard-related use scenarios. Both sets of rules require particularly careful consideration for these cases, including targeted testing in the summative evaluation.

The FDA regards use errors, close calls and use difficulties as central assessment elements in human factors validation testing. Not only errors that actually occurred therefore count. Error-tolerant design is meant to prevent use errors, detect them early or limit their effects and thus complements the use-related risk analysis at the level of error tolerance.

Typical causes of use errors

Use errors rarely arise by chance. In practice, recurring causes can be observed that can be addressed specifically through usability engineering:

• Lack of distinguishability of controls, symbols or messages (e.g., similar-looking ampoules or buttons)
• High cognitive load in stressful situations or under time pressure, for example in a clinical emergency
• Unclear or inconsistent feedback from the system that does not make the actual state clearly recognizable
• Deviations from expectations that users bring from other, similar products (negative transfer)
• Unfavorable environmental conditions such as poor lighting, noise or distraction (see also use environment factors)

Detecting use errors: formative and summative evaluation

Use errors are not discovered only on the finished product but ideally already during development. In formative evaluations, for example with the think-aloud method, early design drafts are tested with representative users to uncover weaknesses before they flow into the final design.

In the summative usability evaluation (validation), it is subsequently checked on the final product under realistic conditions whether critical use errors actually occur with representative user groups. This validation is the regulatory proof required that the residual risks from use errors are acceptable.

Regulatory reference

The handling of use errors is a central component of the usability engineering process according to IEC 62366-1 and is closely interlinked with risk management according to ISO 14971. The EU Medical Device Regulation (MDR) explicitly requires in Annex I that risks from use errors be minimized through suitable design. With its human factors guidance, the FDA takes a comparable approach and, in its validation requirements, focuses in particular on critical tasks where use errors could lead to serious harm.

Frequently asked questions (FAQ)

Sources

• IEC 62366-1:2015+AMD1:2020, Medical devices, Part 1: Application of usability engineering to medical devices
• ISO 14971:2019, Medical devices, Application of risk management to medical devices
• Regulation (EU) 2017/745 on medical devices (MDR)

Related terms

• Abnormal use
• Use-related risk analysis (URRA)
• Hazard-related use scenario
• Summative usability evaluation

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