The Essence of Usability

Usability is generally understood as a term that describes the operability and ease of use of software and other products. In many cases, the ability to operate something easily, without confusion, and without stress is expressed as “good usability” or “high usability.”

However, it is important to note that the international standard on usability, ISO 9241-11, defines it differently from this common understanding. The current version, ISO 9241-11:2018, defines usability as “the extent to which a system, product or service can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.” This definition emphasizes that usability is not simply about ease of use, but about achieving specific goals in specific contexts.

Furthermore, IEC 62366-1:2015+AMD1:2020, the standard specifically addressing usability engineering for medical devices, specifies a process for manufacturers to analyze, specify, develop, and evaluate the usability of medical devices as it relates to safety. In medical device regulations, “effectiveness” and “efficiency” are positioned as critical elements directly linked to safety.

The Specificity of Usability in Medical Devices

The most important aspect of usability engineering for medical devices is achieving “safe” medical devices that are free from use errors. While usability certainly includes elements such as “ease of use,” “user satisfaction,” and “appearance,” these become secondary considerations in the design and development of medical devices. The primary focus must always be on safety.

Interestingly, designing something to be deliberately difficult to use can also be part of usability engineering. For example, disposable lighters are designed with heavy push buttons to prevent fires from spontaneously igniting in bags or from children’s mischief. Similar considerations can apply to medical devices. When safety requires it, adding friction or resistance to certain operations may be the appropriate usability design choice.

Deliberately Making Things Difficult to Use Is Also Usability

The principle that sometimes we must make devices harder to use to make them safer represents a fundamental aspect of usability engineering in regulated industries. This counterintuitive approach recognizes that preventing dangerous actions is more important than convenience.

Practical Implementation

Usability engineering applies to all medical devices. It is not limited to active medical devices (ME equipment), nor is it limited to higher risk classifications—even Class I devices are subject to these requirements. Furthermore, usability engineering encompasses not only software interfaces but all interfaces, including accompanying materials and documentation.

Interfaces include everything perceived through human senses. Visual elements include LCDs (displays), labels, colors, instruction manuals, and educational materials. Auditory elements include alarm sounds. Tactile elements include buttons, switches, and physical forms.

Instructions for use and other accompanying documents containing safety information are critical components of the user interface. These should be considered from the initial stages and addressed within the usability engineering process. They should also be leveraged in the development of training materials.

Consideration of Use Environment and Users

Considering the diversity of use environments is extremely important. For example, an automated external defibrillator (AED) may be used in emergency situations surrounded by a crowd, where there is no time to read instruction manuals. In such cases, efficiency is directly linked to safety. Design must facilitate rapid, correct use under pressure.

Similarly, medical devices such as electrocardiographs used in ambulances must be designed with mobility and vehicular use in mind. Displays must remain readable despite vibration, and controls must be operable while wearing gloves.

AEDs Where Every Second Counts: Efficiency Impacts Safety

The AED exemplifies how usability directly affects patient outcomes. Clear visual and auditory prompts, intuitive electrode placement indicators, and unambiguous control sequences can mean the difference between life and death. This is why usability testing for such devices must include scenarios that simulate the stress and confusion of actual emergency situations.

When examining “reasonably foreseeable misuse” as required by ISO/IEC Guide 51, it is necessary to identify user attributes. Various users must be considered, including people with physical disabilities, people with color vision deficiencies, elderly people, children, pregnant women, and foreigners who speak different languages. It must be verified whether each of these user groups can complete their tasks successfully.

The following table summarizes key user groups and their specific considerations in usability engineering:

User Group	Specific Considerations	Design Implications
Healthcare professionals	High cognitive load, time pressure, multitasking	Clear prioritization of information, unambiguous controls
Patients/lay users	Limited medical knowledge, potential stress or anxiety	Simple instructions, intuitive operation, clear feedback
Elderly users	Reduced vision/hearing/dexterity, potential cognitive decline	Larger displays, higher contrast, tactile feedback, simplified workflows
People with disabilities	Physical limitations, sensory impairments	Accessibility features, alternative input methods, multi-sensory feedback
Non-native speakers	Language barriers	Universal symbols, pictograms, minimal text dependence
Emergency responders	Extreme time pressure, high-stress environment	Rapid operation, clear step-by-step guidance, failsafe mechanisms

Relationship to Risk Management

Usability engineering for medical devices is tightly integrated with risk management processes required by ISO 14971. IEC 62366-1:2015+AMD1:2020 explicitly strengthens the links between usability engineering and ISO 14971:2019 risk management. Use-related hazards identified through usability engineering must be incorporated into the overall risk management file, and risk control measures must address both hazards and use errors.

The usability engineering process identifies potential use errors and use-related hazards, evaluates their associated risks, and implements appropriate risk control measures. These activities are documented in the usability engineering file, which becomes part of the technical documentation required for regulatory submissions.

Formative and Summative Evaluation

The usability engineering process includes both formative evaluation (conducted during development to identify and resolve usability issues) and summative evaluation (conducted to validate that the final design achieves acceptable usability and safety).

Formative evaluation is iterative and occurs throughout the design process. Methods may include expert reviews, heuristic evaluations, and user testing with prototypes. The goal is to identify and correct usability problems as early as possible when changes are less costly.

Summative evaluation, often called usability validation, is conducted with the final design or production-equivalent units. It involves representative users performing critical tasks in simulated use environments to demonstrate that use-related risks have been adequately controlled. This validation provides objective evidence that the device can be used safely and effectively by the intended user population.

Thus, usability engineering for medical devices is not simply the pursuit of ease of use, but a comprehensive safety design approach that anticipates diverse use environments and users. It is established as a systematic analytical methodology for realizing safe medical devices free from use errors, integrated seamlessly with the overall risk management framework.

Note: This article is based on current international standards as of January 2026, including ISO 9241-11:2018, IEC 62366-1:2015+AMD1:2020, ISO 14971:2019, and ISO/IEC Guide 51. Readers should verify that they are working with the most current versions of applicable standards for their specific regulatory jurisdiction.