Over the past two decades, post-market surveillance has revealed concerning trends of adverse events in medical devices, many of which are directly linked to poor design of user interfaces (UI). Devices such as infusion pumps, automated external defibrillators (AEDs), ventilators, and combination products like drug auto-injectors have frequently demonstrated use-related design flaws. These issues have led to critical consequences—including overdoses, incorrect therapy delivery, misdiagnoses, and delays in administering timely treatment.
In response to these challenges, regulatory authorities have emphasized the integration of Human Factors and Usability Engineering (HF/UE) into the medical device design and development process. Although HF/UE has long been employed in industries like aerospace, automotive, and telecommunications (for over 90 years), its formal adoption in the medical field is relatively recent.
HF/UE is centered on understanding and optimizing the interactions between users and devices by taking into account human abilities, limitations, behaviors, and preferences. It involves applying design principles, conducting user studies, and performing rigorous evaluations to ensure that the device interface is safe, effective, and intuitive. The ultimate aim is to reduce use-related risks and enhance user performance and satisfaction.Is Usability Different from Human Factors? How Do These Terms Relate?
While usability engineering and human factors engineering are closely related and often used interchangeably, there are subtle distinctions between them:
- Human Factors Engineering (HFE) is a broader discipline that studies human capabilities and applies this knowledge to system design to improve safety, performance, and satisfaction.
- Usability Engineering (UE) is a subset of HFE that focuses more specifically on the qualities of the user interface—such as learnability, efficiency, memorability, and error tolerance.
In essence, usability is a measurable outcome of applying human factors principles. It refers to how easily and effectively users can interact with a product to achieve their goals. Terms like user-friendly and intuitive describe systems that meet user expectations and support seamless task execution without causing confusion or frustration.
What is the Impact of Usability on Healthcare?
Usability plays a critical role in healthcare outcomes. A medical device with poor usability can lead to:
- Increased user errors
- Longer task completion times
- User frustration and stress
- Delayed or incorrect treatment delivery
- Compromised patient safety
Therefore, usability contributes both to patient safety and business success, making it a strategic focus in medical device development.
How Have Medical Device Regulations Incorporated HF/UE in Regulatory Activities?
In light of the growing number of user interface–related adverse events, regulatory authorities worldwide have made HF/UE an essential component of the medical device approval process.
Manufacturers are now expected to integrate human factors principles into design controls and risk management activities from the earliest stages of product development. Regulatory bodies like the FDA (U.S.) and European authorities have issued specific guidance and expectations, emphasizing the need for usability validation.
What Are the Expected HF/UE Outputs Reviewed by Regulatory Organizations?
To demonstrate compliance with IEC 62366, manufacturers must document the entire Usability Engineering Process (UEP). The standard outlines nine key clauses, each representing a step in the HF/UE lifecycle—from defining user profiles and use environments to identifying hazardous use scenarios and validating the final user interface.
Key deliverables expected by regulatory bodies include:
- Use specification
- User interface characteristics related to safety
- Hazard-related use scenarios
- Use-related risk analysis
- Formative evaluation and iterative design improvements
- Summative (validation) usability testing reports
- Residual risk evaluations
- Traceability to risk management
These outputs are reviewed as part of pre-market submissions and are often tied directly to a device’s risk classification and intended use.
What Are the Basic Activities in the HF/UE Process and Their Alignment with Risk Assessment?
HF/UE activities are typically grouped into three interrelated phases, each aligned with regulatory and risk management frameworks:
Preliminary Analyses
- Identify users, environments, use scenarios, and potential use errors.
- Analyze tasks and workflows to uncover points of failure.
User Interface Design and Evaluation
- Apply human factors design principles to UI components (e.g., screens, buttons, labels).
- Conduct formative evaluations using prototypes with representative users.
- Iterate based on feedback and usability findings.
Simulated Use Testing (Validation)
- Perform summative testing of the final design under realistic conditions.
- Verify that users can perform critical tasks safely and effectively without assistance or prior training.
- These HF/UE activities are tightly integrated with the device’s risk management file as per ISO 14971, ensuring that use-related hazards are identified, mitigated, and verified as acceptable before product release.
Representation of Usability Engineering in Technical Documentation
Human Factors and Usability Engineering (HF/UE) is not just a design philosophy—it is a structured, traceable process that must be well-documented throughout the device lifecycle. Regulatory bodies such as the FDA, European Notified Bodies, and others require concrete HF/UE documentation as part of the technical file or design dossier submitted for product approval.
HF/UE activities are integrated at various stages of the product development process, and each stage contributes specific elements to the technical documentation.
1. Initial Concept Phase: Defining Use Context
At this earliest phase, HF/UE helps ensure that user needs and system goals are correctly captured.
Documentation Includes:
- Use Specification: A detailed description of the intended users, use environments, and intended use of the device.
- User Profiles: Characteristics of the target user groups (e.g., lay users, healthcare professionals).
- Task Analysis: Identification of critical tasks that users must perform safely and effectively.
- Operational Environment Descriptions: Environmental factors (noise, lighting, stress levels) that might affect usability.
Why It Matters:
Early HF/UE integration ensures that the device design is anchored in real-world use scenarios, laying the foundation for safety and effectiveness.
2. Preliminary Hazard Analysis Phase: Risk-Oriented Design
During risk analysis, usability engineering works hand-in-hand with traditional hazard identification and risk management processes.
Documentation Includes:
- Use-Related Hazard Identification: Analysis of how UI issues could result in harm.
- Use Error Analysis: Evaluation of likely errors based on human limitations or interface complexity.
- Link to Risk Management File: Clear traceability between usability risks and control measures documented under ISO 14971.
Why It Matters:
This ensures that use errors are considered as valid sources of risk, and appropriate mitigations (design changes, instructions, training) are implemented and documented.
3. Prototyping and Design Iteration Phase: Formative Evaluation
As concepts turn into functional prototypes, usability testing becomes crucial.
Documentation Includes:
- Formative Study Protocols and Reports: Details of early user tests, including methods, test environments, findings, and design updates.
- Design Rationale Logs: Explanation of UI design decisions based on HF/UE principles.
- Mock-up and Prototype Evaluations: Feedback from simulated use by actual or surrogate users.
Why It Matters:
These documents demonstrate a data-driven, user-centric design approach and show regulators how real user feedback informed the evolving design.
4. Integration into the Final Design File
All HF/UE documentation is ultimately compiled into the Usability Engineering File (UEF), which is either standalone or integrated into the overall Technical File / Design Dossier.
Key Final Outputs:
- Usability Engineering Summary Report
- Summative (Validation) Usability Testing Reports
- Traceability Matrix (linking hazards to usability studies and mitigations)
- Residual Use Risk Justifications
Why It Matters:
Regulators review this section carefully to determine whether the device’s user interface has been adequately validated and whether all critical user-related risks have been addressed.
Inclusion of HF/UE in technical documentation is not optional—it is integral to demonstrating compliance with international standards (e.g., IEC 62366, ISO 14971) and regional regulatory expectations (FDA, MDR, etc.). Its presence from the concept phase to final testing ensures that the device is designed not just for function, but also for safe, intuitive, and effective human interaction.
