Many medical device failures in the field are not caused by the device breaking - they are caused by people using the device in ways the designers did not anticipate. Use errors contribute to a substantial share of device-related adverse events and recalls, which is why human factors and usability engineering (HFE/UE) has become a central expectation of both the FDA and international regulators. Designing a device that is not only functional but safe and usable in the hands of real users is now a regulatory requirement, not a nice-to-have.
The Governing Standards and Guidance
The international standard for usability engineering is IEC 62366-1:2015 (with its 2020 amendment), which defines a process for analyzing, specifying, developing, and evaluating the usability of a medical device as it relates to safety. In the United States, the FDA's guidance "Applying Human Factors and Usability Engineering to Medical Devices" sets parallel expectations, and the FDA has issued additional guidance on the human factors information that should be included in premarket submissions. While the standard and the FDA guidance use somewhat different terminology, they share the same core philosophy: usability is a safety discipline driven by risk.
Use-Related Risk Analysis
Human factors work begins with understanding how the device will be used and where use could go wrong. This includes developing a use specification (intended users, uses, and use environments), identifying user tasks, and conducting a use-related risk analysis to find hazards arising from normal use and from reasonably foreseeable use errors. The output is a set of critical tasks - those tasks where a use error could cause serious harm - which become the focus of the rest of the program. This analysis must be tightly integrated with the device's overall risk management file under ISO 14971.
Formative and Summative Evaluation
HFE relies on two complementary types of user testing:
- Formative evaluations are conducted iteratively during development to identify usability problems early, when the user interface can still be changed inexpensively. They are diagnostic, not pass/fail, and are essential for refining the design.
- Summative (validation) testing is conducted on the final design to demonstrate that the device can be used safely and effectively by representative users performing critical tasks. For FDA submissions, summative studies are typically expected to include approximately 15 participants per distinct user group, performed under realistic conditions.
A frequent and costly mistake is treating the summative study as the entire human factors program. Validation without prior formative work often reveals problems too late, forcing redesign and repeat testing on the critical path to launch.
Analyzing Use Errors and Residual Risk
The value of a summative study lies not only in success rates but in the analysis of every use error, close call, and difficulty observed. Each must be examined to determine whether it could lead to harm, what its root cause was, and whether the design can be improved to mitigate it. Residual use-related risk is then evaluated for acceptability, just like any other risk in the risk management file. Regulators expect to see this reasoning documented, not merely a summary statistic.
Human Factors in the Submission
For devices with significant use-related risk, the FDA expects a human factors engineering report in the premarket submission that ties the entire program together - the use specification, user task and risk analysis, formative and summative methods and results, and conclusions about residual risk. Devices with novel user interfaces, home or lay-user use, or high-harm critical tasks receive the closest scrutiny. Planning this evidence early prevents last-minute surprises during review.
How Sequence Group Can Help
Sequence Group integrates human factors and usability engineering into the design control and risk management process - from use-related risk analysis and formative study planning through summative validation and the human factors engineering report for your submission. Contact us to build usability evidence that protects patients and stands up to FDA review.
Frequently Asked Questions
What is the difference between formative and summative usability testing?
Formative evaluations are conducted iteratively during development to diagnose usability problems early, when the user interface can still be changed inexpensively. They are not pass/fail tests. Summative (validation) testing is conducted on the final device design to demonstrate that representative users can safely and effectively perform critical tasks under realistic conditions. FDA submissions for devices with significant use-related risk typically require summative testing, usually with approximately 15 participants per distinct user group.
What is a "critical task" in human factors engineering?
A critical task is one where a use error could directly cause or contribute to serious patient harm. Critical tasks are identified through the use-related risk analysis conducted at the start of the HFE program, which examines all user tasks to find those where errors have hazardous consequences. These tasks receive focused attention in formative and summative evaluations, and their residual use-related risk must be assessed and documented in the risk management file.
What human factors information does FDA expect in a premarket submission?
For devices with significant use-related risk, FDA expects a human factors engineering report that ties the entire program together - the use specification, user task and risk analysis, formative and summative study methods and results, analysis of use errors observed, and conclusions about residual risk. Devices with novel user interfaces, lay-user or home-use contexts, or high-harm critical tasks receive the closest review scrutiny.