Usability Engineering

Usability Engineering, also known as Human Factors Engineering, is a systematic process required by international standards and regulatory authorities to ensure that medical devices can be used safely and effectively by intended users in the intended use environment. The process involves analyzing, designing, and testing user interfaces to minimize use errors that could lead to harm.

IEC 62366-1:2015 standard:

The primary international standard for usability engineering of medical devices is IEC 62366-1:2015 "Medical devices - Part 1: Application of usability engineering to medical devices." This standard is:
- Recognized by FDA as a consensus standard
- Required for EU MDR compliance
- Adopted globally by major regulatory authorities
- Focused on preventing use errors through design

Key concepts and terminology:

Use error:
An act or omission of an act by a user that leads to a result that was not intended by the manufacturer and is different from the expected user behavior. Use errors can result from:
- Poor user interface design
- Inadequate labeling or instructions
- Confusing controls or displays
- Lack of safeguards against misuse
- Insufficient training or experience

Use-related hazard:
A hazard associated with the user interface, including use errors, misuse, or reasonably foreseeable actions or omissions by the user.

User interface:
All components of the device that users interact with, including:
- Physical controls (buttons, knobs, switches)
- Displays (screens, indicators, alarms)
- Labeling and instructions for use
- Software interfaces
- Connectors and ports
- Packaging (for sterile devices)

Intended users:
The individuals expected to use the device, characterized by:
- Training and education level
- Clinical or technical expertise
- Physical capabilities
- Cognitive abilities
- Sensory abilities (vision, hearing, touch)
- Language and cultural background

Use environment:
The physical, social, and organizational context where the device will be used:
- Clinical settings (hospital, clinic, home)
- Lighting conditions
- Noise levels
- Distractions and interruptions
- Time pressures
- Multi-tasking demands

Usability engineering process:

1. User specification and use environment analysis
- Identify intended users and their characteristics
- Define use environments and conditions
- Identify critical tasks and user goals
- Analyze potential use-related hazards

2. User interface specification
- Design user interface elements
- Develop user interaction sequences
- Create labeling and instructions
- Implement error prevention features
- Design alarms and alerts

3. User interface design and risk analysis
- Conduct preliminary risk analysis of user interface
- Identify use-related hazards and hazardous situations
- Determine which tasks could lead to harm
- Classify hazardous situations by severity
- Identify user interface elements requiring evaluation

4. Formative evaluation (usability testing)
- Conduct iterative testing with representative users
- Observe users performing critical tasks
- Identify use errors and close calls
- Evaluate effectiveness of risk control measures
- Modify design based on findings
- Test early prototypes and refine design

5. Summative evaluation (validation testing)
- Conduct final validation testing with representative users
- Demonstrate that user interface is safe and effective
- Verify that use-related risks are acceptable
- Test with final or production-equivalent devices
- Document that usability goals are met

6. Usability engineering file compilation
- Document all usability engineering activities
- Maintain evidence of design decisions
- Record test protocols, results, and analyses
- Include risk management integration
- Demonstrate compliance with IEC 62366-1

IEC 62366-1 documentation requirements:

The Usability Engineering File must include:

Part 1: Application specification
- Device description and intended use
- User profile specifications
- Use environment description
- User tasks and scenarios
- Known or foreseeable use-related hazards

Part 2: User interface specification
- User interface design rationale
- User interface elements and features
- Control and display descriptions
- Labeling and instructions content
- Error prevention mechanisms

Part 3: Formative evaluation plan and results
- Test objectives and scenarios
- Representative user selection criteria
- Test environment setup
- Use errors observed
- Design modifications implemented

Part 4: Summative evaluation plan and results
- Validation test protocol
- User selection and characteristics
- Pass/fail criteria
- Use errors and close calls
- Analysis of residual risks
- Conclusion on acceptability

Relationship to risk management (ISO 14971):

Usability engineering is integrated with risk management:
- Use-related hazards identified in usability process feed into risk analysis
- Risk control measures implemented through user interface design
- Formative testing verifies effectiveness of risk controls
- Summative testing validates residual risk acceptability
- Usability file cross-references risk management file

Common usability testing methods:

Simulated use testing:
- Users perform realistic tasks with the device
- Observed in controlled test environment
- Critical tasks identified and evaluated
- Use errors documented and analyzed
- Most common method for regulatory submissions

Contextual inquiry:
- Observe users in actual use environment
- Understand real-world workflows and constraints
- Identify unanticipated use patterns
- Valuable for formative evaluation

Cognitive walkthrough:
- Expert review of user interface
- Step-through of user tasks
- Identify potential confusion points
- Supplement to user testing

Heuristic evaluation:
- Expert evaluation against usability principles
- Identify design violations
- Early-stage formative method
- Not sufficient alone for regulatory compliance

Critical tasks and user interface elements requiring evaluation:

IEC 62366-1 requires identification of:

User interface elements of concern:
User interface elements where incorrect use could lead to unacceptable risk. These must undergo rigorous formative and summative evaluation.

Critical tasks:
User tasks where use errors or task failures could result in unacceptable risk. Must be validated in summative testing.

Typical critical tasks for medical devices:
- Programming therapy parameters
- Selecting treatment modes
- Interpreting device outputs or alarms
- Connecting device to patient
- Sterilizing or cleaning device
- Replacing consumables or batteries
- Responding to error conditions

Regulatory requirements:

FDA:
- Recognizes IEC 62366-1 as consensus standard
- Requires human factors information in many submissions
- FDA Guidance: "Applying Human Factors and Usability Engineering to Medical Devices" (2016)
- Human factors validation testing expected for higher-risk devices
- Increased focus on software user interfaces and cybersecurity

EU MDR:
- Annex I (General Safety and Performance Requirements) references usability
- IEC 62366-1 compliance expected for CE marking
- Notified bodies review usability engineering files
- Post-market surveillance includes use error monitoring

Other regions:
- Health Canada, TGA (Australia), PMDA (Japan), and other authorities increasingly require usability engineering evidence
- IEC 62366-1 recognized internationally

Common usability issues in medical devices:

Display and controls:
- Confusing or ambiguous labeling
- Similar-looking controls with different functions
- Inadequate visual feedback
- Poor contrast or readability
- Over-reliance on color coding

Alarms and alerts:
- Too many nuisance alarms (alarm fatigue)
- Unclear alarm priorities
- Difficult-to-silence alarms
- Insufficient alarm distinguishability

Software interfaces:
- Complex navigation structures
- Inconsistent interaction patterns
- Inadequate error messages
- Loss of data during interruptions
- Confirmation dialogs ignored by users

Connectors and connections:
- Reversed or crossed connections
- Compatible but incorrect connectors
- Inadequate locking mechanisms
- Poor visual differentiation

Instructions for use:
- Overly complex or lengthy
- Poor organization and searchability
- Inadequate warnings or precautions
- Insufficient illustrations
- Translation errors

Best practices for usability engineering:

1. Involve users early and often
- Test with representative users throughout development
- Don't rely solely on expert reviews
- Include diverse user populations

2. Test in realistic conditions
- Simulate actual use environments
- Include realistic distractions and time pressures
- Use production-equivalent devices for validation

3. Focus on critical tasks
- Prioritize tasks where errors cause harm
- Allocate testing resources accordingly
- Ensure critical tasks are validated

4. Iterate based on findings
- Modify design when use errors observed
- Re-test after design changes
- Document design evolution

5. Integrate with risk management
- Cross-reference usability and risk files
- Ensure use-related hazards addressed
- Validate risk control effectiveness

6. Maintain comprehensive documentation
- Document rationale for design decisions
- Record all test activities and results
- Demonstrate standards compliance

Advanced usability considerations:

Cybersecurity and usability:
- Balance security measures with usability
- Avoid making secure use too difficult
- Consider authentication burdens
- Minimize security-related use errors

AI/ML device interfaces:
- Communicate algorithm uncertainty appropriately
- Design for explainability and transparency
- Address user trust and over-reliance
- Test interpretation of AI outputs

Home use devices:
- Broader user population (patients, caregivers)
- Unsupervised use environments
- Greater diversity in user capabilities
- More challenging use environments

Mobile medical apps:
- Small screen constraints
- Touch interface challenges
- Distraction-prone environments
- Platform-specific conventions

Usability engineering is essential for medical device safety, preventing use errors that could harm patients. Through systematic analysis, design, and testing following IEC 62366-1, manufacturers ensure devices are safe and effective for their intended users and use environments.