Applying Human Factors and Usability Engineering to Medical Devices

Applying Human Factors and Usability Engineering to Medical Devices

Human Factors Engineering (HFE), also known as Usability Engineering (UE), is an essential component in the development of medical devices. It ensures that devices are designed with users in mind, helping to reduce use-related hazards, enhance patient safety, and ensure regulatory compliance.

In this article, we introduce the core principles of HFE, explore why it is critical in medical device development, and describe key evaluation approaches like formative and summative testing.

What is Human Factors Engineering?

The objective of this discipline is to optimize the user interface such that it enables intended users to use the device correctly, consistently, and with minimal risk of harm.

According to FDA guidance:

"Human factors engineering is the application of knowledge about human behavior, abilities, limitations, and other characteristics of medical device users to the design of medical devices, including mechanical and software-driven user interfaces, systems, tasks, user documentation, and user training to enhance and demonstrate safe and effective use."

This includes, but is not limited to, the physical design of the device, software interfaces, displays, alarms, controls, instructions for use, packaging, and training. HFE ensures that the user interface aligns with users' expectations and capabilities, thereby reducing the potential for user error.

Why is Human Factors Engineering Needed?

Human Factors Engineering (HFE) is essential in medical device development because it addresses use-related risks—hazards that arise not from device failure, but from how users interact with the device. These risks include confusion, misinterpretation, or misuse caused by poor interface design, unclear labeling, or unrealistic assumptions about user capabilities and use environments.

These use-related hazards may arise when:

• Device use requires physical or cognitive abilities that exceed those of the user.
• Device use is inconsistent with the user's expectations or intuition about device operation.
• The use environment affects the operation of the device, and this effect is not recognized or understood by the user.
• The particular use environment impairs the user's physical, perceptual, or cognitive capabilities when using the device.
• Devices are used in ways that the manufacturer could have anticipated but did not consider.
• Devices are used in ways that were anticipated but inappropriate (e.g., inappropriate user habits) and for which risk elimination or reduction could have been applied but was not.

By incorporating HFE into design controls and risk management, manufacturers can proactively identify and mitigate these hazards through iterative analysis, design, and testing.

1. Understanding Users, Use Environments, and Interfaces

To design safe and effective medical devices, manufacturers must analyze:

2. Preliminary Analyses and Evaluations

Preliminary analyses and evaluations help identify what users need to do, how they interact with the device, and where problems might occur, all early in the design process.

Key results of these activities are creating a list of critical tasks that, if done incorrectly or missed, could lead to serious harm. This list changes as the design develops and is used to plan the final human factors validation test.

• Critical Task Identification and Categorization
  The process involves risk-based categorization of user tasks. Techniques such as Failure Modes Effects Analysis (FMEA) and Fault Tree Analysis (FTA) are used to identify how user actions may lead to hazardous situations.
• Identification of Known Use-Related Problems
  Known use-related problems from existing or similar devices should be considered in the design process. Information can be sourced from Customer complaint files, Internal usability studies, Regulatory databases (e.g., FDA MAUDE, MedSun), Published literature and conference proceedings, Expert organizations (e.g., ISMP, ECRI, The Joint Commission).

• Analytical Approaches to Identifying Critical Tasks
  Analytical approaches systematically evaluate expected user interactions and include:

  1. Task Analysis: Decomposing device use into discrete tasks to assess where and how use errors may occur. It considers perceptual, cognitive, and physical aspects of each task.
  2. Heuristic Analysis: Evaluation by human factors specialists against established usability principles to identify design weaknesses.
  3. Expert Review: Analysis conducted by clinical or technical experts based on their knowledge and experience with the device and user population.

• Empirical Approaches to Identifying Critical Tasks:
  Empirical methods gather data directly from users interacting with the device, often via prototypes, and include contextual inquiry and one-on-one interviews.

  Formative Evaluation: Informing Design through Iteration
  Formative evaluations are usability assessments performed during the development of a medical device to guide and refine the user interface before it is finalized. 

  They complement early risk analyses by providing direct insight into user interaction through observation and feedback. Common methods include:

  1. Cognitive Walkthroughs – where users are guided through tasks and asked to verbalize their thought process to reveal confusion or errors.
  2. Simulated-Use Testing – where users independently perform realistic tasks under simulated conditions to evaluate interface design and training effectiveness.

3. Elimination or Reduction of Use-Related Hazards

Use-related hazards should be identified early through preliminary analyses and mitigated, ideally before human factors validation testing using a hierarchy of risk control strategies, as outlined in ISO 14971:

4. Human Factors Validation Testing (Summative Evaluation)

Human factors validation testing, also known as summative evaluation, is a critical and final assessment conducted to confirm that the medical device user interface supporxts safe and effective use by the intended users, for the intended uses, and within the intended environments. This testing is performed after the device design is complete, including the final user interface, labeling, and training materials.

The primary objective is to validate that critical tasks—those which, if performed incorrectly or not performed at all, could result in serious harm—can be carried out correctly and consistently by representative users.

5. Key Documentation Components

Proper documentation is essential to demonstrate compliance with FDA guidance and ISO 62366. The core components include:

1. Usability Engineering File (UEF) — A comprehensive record of usability activities across the device lifecycle, including device description, intended users and environments, user interface design rationale, critical tasks, and use-related risk analyses.
2. Formative Evaluation Plan and Reports — Detail the purpose, methods, and results of usability testing during development, including task analyses, identification of use errors, and design modifications based on findings.
3. Summative Evaluation (Validation) Plan and Report — Documents the final human factors validation testing, covering test protocol, participant demographics, critical tasks, data analysis, root cause evaluation of errors, and residual risk justification.

These records are critical for regulatory submissions and support the safe and effective design of medical devices.