The difference between a formative and summative test

In medical device development, understanding the difference between a formative usability test and a summative usability test (also known as a “human factors validation test”) is essential for product safety and regulatory compliance. While both activities are part of the usability engineering process, they serve very different purposes.

Formative Usability Testing

A formative usability test is conducted during device development and is intended to improve the product design. The goal is to identify use errors, evaluate design concepts, and refine the user interface, labeling, and workflows before design freeze.

Formative usability testing is iterative. You test, adjust the design, and test again. These studies help mitigate use related risks early and strengthen your overall human factors and usability engineering process under IEC 62366-1 and FDA’s final guidance on human factors and usability engineering.

• When: Iteratively during device development
• Participants: Small, flexible sample sizes (typically 6–10 participants)
• Product: Early concepts, prototypes, or draft labeling
• Objective: Explore user interactions, uncover use errors, and refine the design

In simple terms, formative testing is about optimization and reducing use-related risks during device development.

Summative Test (Human Factors Validation Test)

A summative test, also referred to as a human factors (HF) validation test, is performed once the medical device design is finalized. At this stage, the device, labeling, and training should be production-equivalent.

The objective of the summative test is not to improve the design, but to demonstrate that intended users can safely and effectively use the device in the intended use-environment(s). The goal of the summative test is to eveluate whether intended users can perform all critical tasks in realistic use conditions. A critical task is a user task that if performed incorrectly or not performed at all, could cause serious harm to the patient or user, such as injury, death, or compromised care.

• When: After the design is finalized
• Participants: Typically ≥15 participants per distinct user group (per FDA expectations)
• Product: Final, production-equivalent device (including labeling and packaging)
• Objective: Validate that critical tasks can be performed without unacceptable use-related risks

Unlike formative testing, summative testing is confirmatory and regulatory-driven. The results are used to support submissions to regulatory bodies such as the FDA or notified bodies under MDR.

In short, a summative usability test confirms whether the final design of the medical device is safe for the intended users, uses, and use environments.

Conclusion

Formative and summative usability testing are not interchangeable. They serve different purposes within the human factors and usability engineering process. Formative testing reduces risk during development, while the human factors summative test demonstrates that critical tasks have been mitigated to the extent feasible and residual risks are acceptable in the final design.

	Formative testing	Summative testing
When	Early and often during development	After design is finalized
Number of participants	Flexible (6 to 10 participants)	At least 15 participants per user group (FDA)
Product	Prototype, draft labelling	Production-equivalent final product
Goal	Identify and mitigate use-related risks	Validate safe and effective use

When both studies are planned strategically, manufacturers not only strengthen their regulatory submissions but also create safer and more intuitive medical devices. Reach out below to understand how we can support your human factors and usability engineering needs.