Usability Engineering

Usability engineering is the structured process medical-device manufacturers use to analyze, specify, design and evaluate how people interact with a device. Standardized by IEC 62366-1, it treats the complete user interface as a potential source of safety risk and helps manufacturers identify and reduce foreseeable use errors before release.

What is usability engineering?

Usability engineering is the discipline of designing a medical device around the abilities, limitations, expectations and behavior of the people who will use it. In medical devices, the terms usability engineering and Human Factors Engineering (HFE) are generally used interchangeably.

The process considers the complete interaction among:

• The device
• Its intended users
• The tasks users perform
• The environment in which it is used
• The information users receive
• The decisions users must make
• The actions users take
• The consequences of use errors

The medical-device user interface includes more than screens and buttons. It covers every element with which a user interacts, including:

• Displays
• Controls
• Touchscreens
• Alarms
• Indicators
• Connectors
• Tubing and cartridges
• Packaging
• Labels
• Accessories
• Setup procedures
• Cleaning and maintenance activities
• Training materials
• The Instructions for Use (IFU)

Usability engineering runs alongside design controls and risk management throughout development. It is not a cosmetic design activity performed after the device’s engineering has been completed.

The central principle is straightforward: many medical-device incidents arise not from a failed component but from a foreseeable interaction problem that leads to use error. A well-designed interface makes correct use easier and dangerous mistakes less likely.

Usability versus general user experience

Usability engineering under IEC 62366-1 focuses primarily on safety. It evaluates whether problems with the user interface could cause or contribute to harm.

General user-experience design may also consider:

• Visual appeal
• Convenience
• User satisfaction
• Brand consistency
• Workflow efficiency
• Product preference
• Commercial differentiation

These qualities remain valuable, but IEC 62366-1 concentrates on usability as it relates to safety. IEC 62366-2 provides broader guidance that can also address usability considerations beyond safety.

Why usability engineering matters

Use error is a significant contributor to medical-device adverse events, complaints and recalls. A device can perform perfectly from an electrical or mechanical perspective and still be unsafe if users cannot understand or operate it reliably.

Examples include:

• An infusion-pump screen that makes the programmed dose difficult to confirm
• Two similar connectors that can be attached incorrectly
• An alarm that users cannot hear or interpret
• A control that can be activated accidentally
• A home-use device whose instructions exceed the user’s health-literacy level
• A display that presents critical information with insufficient contrast
• Packaging that damages or contaminates a device during opening
• A maintenance procedure that allows incorrect reassembly

These are design problems, not simply user mistakes.

Regulators expect manufacturers to identify use-related hazards, develop interface requirements, evaluate designs with representative users and demonstrate that critical tasks can be completed safely.

Weak usability engineering can lead to:

• FDA deficiency requests
• Notified-body findings
• Additional validation studies
• Late interface redesign
• New tooling
• Labeling changes
• Expanded training requirements
• Delayed clearance or certification
• Post-market complaints
• Recalls or field corrections

Finding a usability problem during an early concept review is relatively inexpensive. Finding the same problem during final validation may require redesign, repeated risk analysis, new test units and another summative study.

How usability engineering works

IEC 62366-1 defines a usability-engineering process that progresses from understanding users and environments to validating the final user interface.

1. Define the use specification

The use specification describes the context in which the device will operate. It should be consistent with the device’s intended use and regulatory claims.

It normally identifies:

• Medical indication
• Intended patient population
• Intended users
• Use environments
• Operating principle
• User-interface characteristics
• Tasks users must perform
• Relevant training
• Expected frequency of use
• Potential emergency situations

The use specification establishes the foundation for the remaining usability work.

2. Define user profiles

User profiles describe the relevant characteristics of each intended user group.

Possible user groups include:

• Physicians
• Nurses
• Laboratory personnel
• Emergency responders
• Service technicians
• Caregivers
• Patients
• Members of the general public

Relevant characteristics may include:

• Education
• Clinical training
• Language
• Health literacy
• Technical experience
• Physical strength
• Dexterity
• Vision
• Hearing
• Cognitive ability
• Experience with similar devices

The profiles should reflect the actual intended population and users, including vulnerable groups where applicable. Convenient participants who do not match the real user characteristics can produce misleading study results.

3. Describe the use environments

Use environment can significantly affect device interaction. A hospital operating room, ambulance, home and diagnostic laboratory present different constraints.

Relevant environmental characteristics include:

• Lighting
• Noise
• Space limitations
• Distractions
• Time pressure
• Protective clothing
• Temperature
• Humidity
• Motion or vibration
• Availability of assistance
• Network connectivity
• Cleanliness requirements

The environment used during evaluation should reproduce the factors capable of influencing critical tasks.

4. Identify user-interface characteristics

Review all interface features that could affect safe and effective use.

This review covers:

• Physical controls
• Displays and menus
• Alarm systems
• Symbols
• Labels
• Accessories
• Connectors
• Packaging
• Setup
• Calibration
• Cleaning
• Maintenance
• Device status information
• Training
• Instructions

The team should examine how users perceive information, interpret it, make decisions and perform actions.

5. Identify known and foreseeable use problems

Sources may include:

• Complaints involving similar products
• Recall databases
• Adverse-event reports
• Published literature
• User interviews
• Contextual observation
• Expert reviews
• Previous usability studies
• Service records
• Known interface conventions
• Competitive-device analysis

The team should not assume that lack of complaints means the interface is safe. Some problems may be foreseeable even if they have not yet produced a documented incident.

6. Conduct use-related risk analysis

Use-related risk analysis connects user actions and interface characteristics to hazards and potential harm.

The analysis considers:

• What the user is trying to accomplish
• What action or omission could occur
• Why the use error could happen
• Which hazardous situation could result
• The possible harm
• Existing risk controls
• Whether additional interface changes are needed

IEC 62366-1 usability work operates alongside ISO 14971 risk management. Use-related risks should remain connected to the main risk-management file rather than being maintained as an isolated usability document.

7. Identify hazard-related use scenarios

A hazard-related use scenario describes a sequence of user actions and device responses that could result in a hazardous situation or harm.

It should include:

• User
• Task
• Interface
• Use environment
• Foreseeable use error
• Resulting hazardous situation
• Potential harm

These scenarios help determine which tasks require the greatest attention during interface design and validation.

8. Identify critical tasks

A critical task is a user task that, if performed incorrectly or omitted, could cause serious harm or compromise medical care.

Examples may include:

• Entering a medication dose
• Connecting a patient circuit
• Responding to a critical alarm
• Interpreting a diagnostic result
• Starting or stopping therapy
• Installing a disposable component
• Confirming device status
• Cleaning a reusable patient-contact part

The rationale for selecting critical tasks should be documented and traceable to the use-related risk analysis.

9. Establish the user-interface specification

The user-interface specification converts risk-analysis findings into design requirements.

Requirements may cover:

• Control dimensions and spacing
• Display contrast
• Alarm priority
• Connector keying
• Menu structure
• Error messages
• Confirmation screens
• Label content
• Packaging sequence
• Training
• Instructions
• Accessibility
• Feedback following user action

Each safety-related interface requirement should connect to the hazard or use error it is intended to control.

10. Prepare the user-interface evaluation plan

The evaluation plan defines how the interface will be assessed during development and validation.

It may specify:

• Formative activities
• Summative-validation strategy
• Participant profiles
• Use environments
• Critical tasks
• Data-collection methods
• Acceptance criteria
• Known-use problems to evaluate
• Study responsibilities
• Documentation requirements

Planning early ensures that the team can recruit appropriate users, prepare representative test units and simulate the use environment accurately.

Formative usability evaluation

Formative evaluation occurs during design. Its purpose is to discover problems and guide improvement while changes are relatively inexpensive.

Methods may include:

• Expert review
• Cognitive walkthrough
• User interviews
• Workflow observation
• Paper-interface evaluation
• Simulated-use sessions
• Comparative design studies
• Label-comprehension testing
• Early alarm testing
• Packaging evaluation

Formative studies can use an early prototype if it represents the interaction being evaluated. Not every formative study requires a production-equivalent device.

A formative evaluation should identify:

• Where users hesitate
• What they misunderstand
• Which tasks they omit
• Where the interface encourages an unsafe action
• Whether users notice and recover from errors
• Whether instructions and training provide adequate support

Several focused formative rounds are generally more valuable than one large study performed immediately before validation.

Summative usability validation

Summative evaluation—often called human-factors validation or usability validation—is the final assessment of the production-intent user interface.

It should use:

• Representative users
• A production-equivalent interface
• Realistic use environments
• Realistic training
• Critical tasks
• Defined data-collection methods
• Controlled study procedures

Summative usability validation forms part of the wider verification and validation evidence demonstrating that the device meets user needs and can be operated safely.

During the study, researchers evaluate:

• Use errors
• Close calls
• Task failures
• Difficulties
• Participant comments
• Root causes
• Whether observed problems could result in harm

The objective is not merely to calculate a task-success percentage. The team must analyze why problems occurred and whether residual use-related risks remain acceptable.

Traceability in usability engineering

Traceability should connect the complete usability process:

Use specification → User profiles → Known problems → Hazards → Hazard-related use scenarios → Critical tasks → Interface requirements → Formative findings → Summative evidence

A maintained Requirements Traceability Matrix (RTM) can connect safety-related interface requirements and risk controls with their supporting evaluation evidence.

Traceability helps reviewers confirm that:

• Every critical task was evaluated.
• Every identified use-related risk has a control.
• Every relevant control was implemented.
• Validation covered the final interface.
• Observed errors received appropriate analysis.
• Design changes were assessed for their effect on earlier evidence.

Applicable standards and FDA guidance

IEC 62366-1

IEC 62366-1:2015, including Amendment 1:2020, defines the usability-engineering process for medical devices as it relates to safety.

IEC 62366-2

IEC 62366-2 is a supporting technical report providing broader guidance on applying usability-engineering methods.

IEC 60601-1-6

IEC 60601-1-6 applies the IEC 62366-1 usability process to medical electrical equipment.

ISO 14971

ISO 14971 governs medical-device risk management. Use-related hazards, hazardous situations and risk controls should connect to the manufacturer’s overall risk-management process.

ISO 13485 and FDA QMSR

ISO 13485 establishes quality-system requirements for controlled device design and development. The FDA QMSR incorporates ISO 13485:2016 by reference through 21 CFR 820.10.

FDA guidance

FDA’s 2016 guidance, Applying Human Factors and Usability Engineering to Medical Devices, describes recommended human-factors processes intended to reduce use-related risks.

FDA issued the final guidance Content of Human Factors Information in Medical Device Marketing Submissions on May 29, 2026. It provides a risk-based framework for determining the human-factors information to include in submissions such as 510(k)s, De Novo requests, PMAs and Humanitarian Device Exemption applications.

Common challenges and best practices

Starting too late

The most common mistake is treating usability engineering as a study performed after the interface has been finalized.

Start during concept and requirements development so findings can influence architecture, controls, displays, connectors, packaging and instructions.

Confusing formative and summative evaluation

Formative evaluation finds and fixes interface problems. Summative evaluation validates the final production-intent interface.

A successful formative study cannot replace final validation.

Recruiting unrepresentative users

Participants should match the characteristics that affect device use. Convenient colleagues, engineering staff or clinicians from the wrong specialty may not represent the intended users.

Using an unrealistic environment

Environmental conditions can change performance. A quiet conference room may not represent an emergency department, ambulance or home.

Weak connection to risk management

A validation protocol should not be based solely on common workflows. It must cover the critical tasks and hazard-related scenarios identified through risk analysis.

Relying on training or labeling

Training and instructions can support safe use, but they should not substitute for a feasible interface improvement. Risk controls should follow the applicable hierarchy, with safe design prioritized.

Changing the interface after validation

A post-validation change to a control, screen, alarm, label, connector or instruction may affect critical tasks. Conduct documented impact analysis to determine whether additional evaluation is required.

Treating user error as participant blame

A use error may reveal that the interface does not adequately support users. Investigate the interaction and its root cause instead of concluding that the participant was careless.

Usability-engineering best practices

Strong programs generally:

• Begin usability work during concept development.
• Define intended users and environments clearly.
• Observe real workflows where possible.
• Include known-use problems from comparable devices.
• Connect use-related risks to the main risk file.
• Translate risk controls into measurable interface requirements.
• Conduct multiple formative evaluations.
• Recruit representative users.
• Simulate realistic conditions.
• Freeze the production-intent interface before summative validation.
• Analyze the root cause of every use error and close call.
• Maintain traceability through the complete process.
• Assess usability impact after every relevant design change.
• Revisit use-related risk using post-market information.

How SJML helps with usability engineering

SJML integrates usability work into its medical device design and engineering process instead of treating it as a final documentation activity.

Engineering teams support user-needs analysis, use specifications, interface requirements, formative evaluation and preparation for summative validation across mechanical, electronics, embedded and software design. IEC 62366-1 activities are connected with ISO 14971 risk management and phase-gate development controls.

SJML’s medical device compliance services help align human-factors documentation and submission evidence with the relevant FDA, EU MDR, ISO 13485 and regulatory-pathway requirements.

In-house laboratories also support related electrical-safety, EMC, reliability and environmental evaluation within the same development program. Structured change control helps protect the validity of usability evidence as the device progresses toward release.

Frequently asked questions