SOP Usability Engineering

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Summary

This Standard Operating Procedure (SOP) establishes a systematic approach to usability engineering throughout the medical device lifecycle, ensuring compliance with IEC 62366-1 standards. It defines processes for understanding user needs, conducting formative and summative usability evaluations, and integrating usability considerations into design and risk management to prevent use errors that could compromise patient safety.

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Why is SOP Usability Engineering important?

Use errors are a significant cause of medical device incidents and patient harm. Regulatory authorities recognize that even well-designed devices can fail if users cannot operate them safely and effectively in real-world conditions. Poor usability can lead to medication errors, misdiagnosis, delayed treatment, or device abandonment when patients and healthcare providers struggle with complex interfaces.

This SOP is essential because it provides systematic methods for understanding user needs, identifying potential use errors, and validating that your device can be used safely by its intended users. IEC 62366-1 compliance demonstrates that you’ve conducted appropriate usability engineering activities proportional to the risk associated with potential use errors.

Integration with risk management ensures that usability considerations influence design decisions throughout development, rather than being addressed as an afterthought. This proactive approach significantly reduces the likelihood of use-related safety issues reaching the market.

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Regulatory Context

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Guide

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Understanding User-Centered Design Principles

User identification forms the foundation of effective usability engineering. Define primary users (those who directly operate the device), secondary users (those who assist or supervise), and tertiary users (those affected by device use). Consider user characteristics including medical training, technical experience, physical capabilities, cognitive abilities, and environmental constraints.

Use context analysis examines where, when, and how your device will be used. Emergency situations require different interface approaches than routine clinical procedures. Consider lighting conditions, time pressures, multitasking demands, and potential distractions that could affect user performance.

Task analysis breaks down device use into specific steps and decision points. Identify critical tasks where use errors could result in serious harm, and focus usability engineering efforts on these high-risk interactions.

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Implementing Systematic Usability Planning

Usability requirements should be specific, measurable, and tied to safety outcomes. Rather than vague statements like “easy to use,” define requirements such as “95% of users can complete initial setup within 10 minutes with no more than one error.”

Use scenario development creates realistic contexts for usability evaluation. Scenarios should reflect actual clinical workflows, time pressures, and environmental conditions. Include both normal use and foreseeable misuse situations.

Risk-based approach prioritizes usability efforts based on potential harm. Focus most attention on critical tasks and use situations where errors could impact patient safety or treatment effectiveness.

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Conducting Effective Formative Usability Evaluation

Iterative testing throughout development identifies usability issues early when they’re easier and less expensive to correct. Use low-fidelity prototypes for initial concept evaluation and high-fidelity prototypes for detailed interface testing.

Representative user recruitment ensures testing reflects your actual user population. Include users with varying experience levels, physical capabilities, and work environments. Avoid using only expert users or laboratory staff.

Realistic use conditions improve the validity of usability findings. Test in simulated clinical environments when possible, include realistic time pressures, and allow multitasking that reflects actual use conditions.

Use error identification focuses on safety-critical failures rather than minor usability preferences. Document instances where users perform incorrect actions, misinterpret information, or fail to complete critical tasks.

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Planning and Executing Summative Usability Validation

Summative testing validates that your final design can be used safely and effectively by intended users. This testing should use the final user interface design with representative users performing realistic tasks.

Critical task validation demonstrates that users can perform safety-critical functions correctly. Define acceptance criteria for each critical task, typically requiring high success rates (e.g., 95-100%) with minimal use errors.

Use environment simulation creates realistic testing conditions that reflect actual use environments. Include appropriate lighting, noise levels, time pressures, and workflow interruptions.

Statistical considerations ensure adequate sample sizes and appropriate analysis methods. For critical tasks, use confidence intervals and statistical tests appropriate for your acceptance criteria.

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Integrating Usability with Risk Management

Use-related risk analysis identifies potential hazards associated with use errors, use omissions, or misuse. Consider both direct effects (incorrect therapy delivered) and indirect effects (delayed treatment due to device abandonment).

Risk control measures can include design improvements, protective measures (alarms, confirmations), or user information (training, labeling). Design controls are generally more effective than relying solely on user training.

Residual risk evaluation determines whether remaining use-related risks are acceptable given the device’s intended benefits. Some use errors may be unavoidable, but their probability and consequences must be acceptable.

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Managing Usability Documentation and Compliance

Usability Engineering Information File (UEIF) contains all usability-related documentation including user research, requirements, test plans, test results, and design rationale. Maintain this file throughout the device lifecycle.

Traceability connects user needs through usability requirements to design decisions and validation results. This traceability supports regulatory submissions and demonstrates systematic usability engineering.

Post-market usability surveillance monitors real-world use errors and usability issues. Integrate usability data collection with your complaint handling and post-market surveillance systems.

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Addressing Software-Specific Usability Considerations

User interface consistency across software modules reduces learning burden and error potential. Establish design standards for navigation, terminology, visual design, and interaction patterns.

Error prevention and recovery capabilities help users avoid mistakes and recover from errors gracefully. Include input validation, confirmation dialogs for critical actions, and clear error messages with recovery guidance.

Accessibility considerations ensure your software can be used by individuals with varying abilities. Consider visual, auditory, motor, and cognitive accessibility requirements relevant to your user population.

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Example

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Scenario

You’re developing a mobile application for insulin dose calculation that will be used by diabetes patients for daily dose management. The app calculates insulin doses based on blood glucose readings, carbohydrate intake, and individual patient parameters. Here’s how usability engineering applies:

User Analysis: Primary users are adults with Type 1 diabetes, ranging from newly diagnosed to experienced patients. Secondary users include caregivers and family members. Consider varying ages (18-80), technology experience levels, and potential visual or dexterity limitations.

Critical Task Identification: Calculate correct insulin dose based on inputs, recognize and respond to dose calculation alerts, enter accurate blood glucose and carbohydrate data, and respond appropriately to error conditions.

Formative Testing: Test early prototypes with diabetes patients using realistic scenarios like calculating pre-meal doses under time pressure. Identify interface elements that cause confusion, data entry errors, or misinterpretation of dose recommendations.

Risk-Based Focus: Prioritize testing scenarios where use errors could lead to hypoglycemia (too much insulin) or hyperglycemia (too little insulin). Test edge cases like very high or low glucose readings, unusual meal patterns, and system error conditions.

Summative Validation: Conduct final testing with 15-20 representative users performing realistic dose calculation tasks. Achieve 95% success rate for critical dose calculation tasks with no safety-critical use errors.

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Example Usability Requirements

Dose Calculation Accuracy:

• 98% of users can successfully calculate insulin dose for typical meal scenarios within 2 minutes
• Users correctly interpret dose recommendations in 99% of test scenarios
• Zero instances of users administering insulin doses that differ from calculated recommendations by >20%

Error Recognition and Recovery:

• 95% of users correctly respond to high/low glucose alerts within 30 seconds
• Users successfully recover from data entry errors in 90% of instances
• No user proceeds with insulin administration when app displays error conditions

Data Entry Validation:

• Users enter blood glucose values within ±5% of actual readings in 95% of attempts
• Carbohydrate estimation accuracy within ±10g for 90% of meal entries
• 100% of users successfully use alternative input methods when initial entry fails

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Example Test Protocol

Participants: 18 adults with Type 1 diabetes, mixed experience levels (6 newly diagnosed <6 months, 6 intermediate 6-24 months, 6 experienced >2 years)

Test Scenarios:

1. Routine pre-meal dose: Calculate insulin for typical breakfast with normal glucose reading
2. High glucose correction: Calculate dose when glucose reading is above target range
3. Low glucose management: Respond appropriately when glucose reading indicates impending hypoglycemia
4. System error recovery: Handle app error during dose calculation process
5. Complex meal calculation: Calculate dose for meal with multiple carbohydrate sources

Success Criteria:

• Task completion rate >95% for critical tasks
• Zero safety-critical use errors (incorrect dose administration)
• User satisfaction rating >4.0/5.0 for ease of use
• All users demonstrate correct understanding of dose recommendations

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Q&A