Usability (German: Gebrauchstauglichkeit) describes, according to IEC 62366-1, a characteristic of the user interface that facilitates use and thereby establishes effectiveness, efficiency and user satisfaction in the intended use environment. For medical devices, usability is not only a comfort feature. Where characteristics of the user interface influence safe use, it is a safety-relevant component of product design.
Definition according to IEC 62366-1 and ISO 9241-11
Two standards define usability, with a subtle but consequential difference.
IEC 62366-1 understands usability as a characteristic of the user interface that facilitates use and thereby establishes effectiveness, efficiency and satisfaction in the intended use environment. The standard thus looks at a characteristic of the user interface but assesses it in interplay with user, task and use environment.
ISO 9241-11, by contrast, defines usability as the extent to which a system can be used by specified users in a specified context of use to achieve specified goals effectively, efficiently and with satisfaction. Here the focus is on use in context.
For practice this means: Usability is not an absolute product property. The same device can be usable for an intensive care nurse and unusable for a lay person in the home environment. Without a defined user group, task and context of use, the statement “the product is usable” is empty of content.
The three dimensions of usability
- Effectiveness: Do users reach the intended goal completely and correctly? Measured, for example, as task success rate or error rate. For medical devices this is the most safety-critical dimension.
- Efficiency: With how much effort is the goal reached? Typical indicators are task time, number of operating steps or calls for help. In emergency situations, efficiency itself becomes safety-relevant.
- Satisfaction: How do users experience the interaction? Captured through standardized questionnaires. Satisfaction is important for acceptance and adherence but is not suitable as an acceptance criterion for safety.
A common misunderstanding: A high satisfaction score does not compensate for observed use errors. In the summative evaluation, what counts is whether safety-relevant tasks were completed without errors, not how pleasant the operation felt.
Why usability is safety-relevant
In other industries, poor usability is a comfort or conversion problem. In medical technology it is a cause of harm. Use errors with infusion pumps, mix-ups in dosing or overlooked alarms are among the recurring reasons for reports in vigilance databases such as the MAUDE database.
IEC 62366-1 therefore consistently treats usability from a risk perspective: Not every inconvenience is relevant, but every design weakness that can lead to a hazardous situation must be identified, controlled and demonstrated. The link to risk management according to ISO 14971 is thus not an add-on but constitutive.
What is decisive is the change of perspective: In the understanding of the standard, a use error is not a failure of the user but an indication of a weakness in the user interface. Merely pointing out that the user should have read the instructions for use is not sufficient justification for controlling a use-related risk. Safety information is permissible but subordinate to safe design and protective measures.
Usability presupposes that information can be perceived, correctly understood and translated into suitable actions, the logic of perception-cognition-action. In the usability engineering process, it is therefore documented traceably from the use specification through task analysis and use-related risk analysis to the summative evaluation.
Usability, UX and ergonomics
The three terms overlap but are not congruent:
- Usability concerns goal-directed use during the interaction: measurable, task-related and, in the regulatory context, safety-driven.
- User experience (UX) is broader and includes expectations before use, emotions, brand perception and memory after use. UX is relevant for acceptance and market penetration but is not the subject of the normative evidence.
- Ergonomics is the scientific discipline that studies the interaction between humans and systems and derives design principles from it, physical, cognitive and organizational.
For the usability engineering file, only the first category counts. For product success, all three count.
How usability is measured
Usability is not claimed but observed. An important method is the usability test with users from the intended user groups who work on realistic tasks in a realistic environment. Depending on the question and risk profile, further qualitative or quantitative evaluation methods can be required.
- Effectiveness: task success rate, number and severity of use errors, abandonments.
- Efficiency: task time, number of interaction steps, frequency of assistance.
- Satisfaction: standardized questionnaires such as the System Usability Scale (SUS) with ten items and a scale score from 0 to 100.
Methodologically, a distinction is made between formative evaluation during development and summative evaluation as the final proof. Analytical methods such as the cognitive walkthrough or heuristic evaluations are used in addition. They do not, however, replace the observation of real users.
Central to all methods is the root cause analysis: A counted error without an understood cause provides no basis for a design decision.
Regulatory requirements
The MDR (Regulation (EU) 2017/745) requires in Annex I, among other things, that risks from use errors be reduced as far as possible and that products be designed ergonomically and taking into account the knowledge and abilities of the intended users. For in vitro diagnostic devices, the same applies under the IVDR, with particular weight on self-tests by lay persons.
The established route to evidence is IEC 62366-1. As of October 2026, it is not listed as a harmonized standard under the MDR but is regarded as the recognized state of the art. For the US market, the FDA human factors guidance sets out its own expectations, in particular regarding the identification of critical tasks.
For medical devices, usability is not a comfort topic but a safety-relevant product characteristic, defined through effectiveness, efficiency and satisfaction, always related to specific users, tasks and contexts. It is demonstrated through observed use, not through satisfaction scores.
Frequently asked questions (FAQ)
What is the difference between usability and “Gebrauchstauglichkeit”?
They are the same thing: “Gebrauchstauglichkeit” is the German equivalent of the English term usability. In German-language regulatory documents, “Gebrauchstauglichkeit” is preferred because it is the term used in the translated version of the standard.
Is good usability the same as good design?
No. Usability is measurable and task-related, whereas good design additionally comprises aesthetics, brand impact and emotional quality. A visually appealing product can have considerable usability deficiencies, and vice versa.
Is a good SUS score sufficient as proof of usability?
No. The System Usability Scale measures subjective satisfaction. The regulatory evidence is based on observed use errors in safety-relevant tasks and their root cause analysis, not on questionnaire values.
Does usability also apply to the instructions for use?
Yes. According to IEC 62366-1, the instructions for use are part of the user interface and are subject to the same requirements as displays and controls.
Who decides what is “usable enough”?
The manufacturer defines the acceptance criteria in advance in the evaluation plan, derived from the use-related risk analysis and risk management. The notified body (the EU conformity assessment body) checks whether these criteria are appropriate and derived in a comprehensible way.
Do you want to demonstrate the usability of your medical device robustly, from context analysis to summative evaluation? We support you methodologically and in terms of regulation.
More about our usability engineeringSources
- 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
- ISO 9241-11:2018, Ergonomics of human-system interaction, Part 11: Usability: Definitions and concepts
- Regulation (EU) 2017/745 on medical devices (MDR)
- Regulation (EU) 2017/746 on in vitro diagnostic medical devices (IVDR)
- FDA Guidance: Applying Human Factors and Usability Engineering to Medical Devices
- FDA MAUDE, Manufacturer and User Facility Device Experience Database
Related terms
- IEC 62366-1
- Use error
- User interface
- Context of use
- Summative usability evaluation
- User-centered design