Human Factors in Design: How Design Changes Impact Human Factors

With the complexity of new technologies, expanded regulations and guidance, and improved methods of tracking product performance on the market, design changes are expected to occur throughout the product lifecycle. Many manufacturers know to address impacts on the physical design or manufacturing process but may not be as familiar with how to evaluate the impact on their human factors and usability efforts. With that in mind, here are four tips to consider when evaluating post-validation (or post-market) design changes from a human factors engineering perspective:

1) Understand the Full Scope of Change

When assessing design changes for impact on usability, the scope of the change must be understood by the entire cross-functional team (CFT). A change that may appear to be limited in scope initially, may expand to include additional ancillary changes to accommodate the product modification.

For example, let’s consider a design change in which a manufacturer adds a new sensor inside their device to detect internal errors. Let’s imagine that the user would not interact with the sensor at any point when using the device. During design change planning, the CFT knows that elements such as design output changes, design verification, risk management, and design transfer activities must be performed in support of the modification.

But the device user interface shouldn’t be impacted by this change, right?

Many CFTs might consider this a fairly limited change that would be unlikely to impact any user interactions. However, it may be prudent to consider ancillary impacts to the change that may not be captured in the initial focus or intent. For this example, some questions to consider about the effects of the new sensor may include:

  • Are there error codes that are displayed to the user if the internal sensor detects an issue?

    • Does the user understand the error code that would be displayed?

    • Does the user need to respond or address this error code? If so, how?

  • Could there be a significant number of errors displayed that could overwhelm/distract the user?

  • If there are no specific error codes, what happens to the device? Does it stop?

    • What information does the user have to respond to this outcome?

    • Are there comparable recovery methods that have been previously assessed?

When looking closer at this change, it may be determined that there are additional impacts from the change that the CFT did not originally anticipate.

Teams should also keep in mind that changes to the design of the device itself (mechanical, electrical, chemical, software, etc.) are not the only configuration changes that can be made! Labeling and packaging elements are still design outputs, and updates to those elements would be considered a configuration change to the product. These represent key components of the product user interface and could impact user interactions if changed.

2) Create a Robust CFT and Incorporate HF Review into Design Change Planning

Due to the scalable nature of design change planning, teams should consider including Human Factors (HF) representatives or individuals who have knowledge of human factors engineering as part of the project team to ensure use-related impacts are evaluated. If there are limited resources across HF teams, consider:

  • Adding HF training for other CFT members that are required to review and approve change control packages to help determine when to pull in human factors CFT members into the evaluation.

  • Ensuring that use-related risk review is included as a required element of the risk management review, not just design or process-specific risks.

In order to assess use-related impact, it is important to include human factors-related elements in the design change planning system to ensure their completion. These elements may be related to associated human factors deliverables, task/sub-tasks, or other methods of documentation in the design change planning system. Adding specific considerations for human factors impact assessments will require the CFT to address impacts if they exist or justify why no impacts are expected based on review of the user interface, user interactions, and use-related risks. It is helpful to provide that framework directly in the design change planning system to ensure it is not overlooked.

Keep in mind that human factors evaluation (from a regulatory perspective) is primarily driven by use-related risk. A change to the user interface that does not modify a user need does not mean that human factors evaluation can be excluded. Additional human factors evaluation may be necessary to evaluate use-related risk associated with the design change.

3) Evaluate Based on Scope and Risk

Now that the project utilizes a full CFT with all necessary members, as well as a full understanding of the scope of change, a review of the change and its impacts may occur. For human factors-related evaluations, the following flow diagram may be helpful to consider specific aspects of the change:

4) Scale the HF Activity

After the design change has been evaluated, it may be determined that there are use-related impacts resulting from the change. In some cases, a validation study (or supplemental validation), may be recommended to provide evidence that the change is acceptable. If changes occur such that:

  • New/modified critical tasks are introduced, where “critical task” is defined to include tasks that, if performed incorrectly or not performed at all, would or could cause serious harm

  • New/modified UI risk control measures are introduced to mitigate use errors associated with critical tasks

  • The change is driven by use-related performance data such as post-market surveillance, etc.,

  • Intended users/use environments are expected to change,

then testing is recommended to support that the device remains safe and effective for intended users and that the benefits still outweigh the risk. A smaller scale of study may be acceptable to evaluate the effects of the change specifically, however, consideration should be made regarding the possibility of unintended consequences or issues derived from the change when developing the test strategy. [3,4]

Note that there are modifications to the product design that do not require additional human factors studies or evaluation. These are often related to changes outside of the user interface that do not alter any use-related characteristics of the device or associated risks. Examples may include internal device changes with no user interaction, such as tolerance changes of an internal mechanical part or component changes within internal electronics. If a review of the design change indicates that this is the case, justification should be included as part of the design change record to clarify why there would be no impact on existing validations.[3]


Keep in mind that the lack of a full evaluation for each change may result in serious harm to the user or patient. Releasing an updated design configuration to market without a comprehensive evaluation adds difficulty in controlling risk in the market after the fact. It is known that using post-market data to address use-related product performance is often difficult due to unclear information, weak reporting systems, and coding/trending that may not adequately identify when use errors may be occurring.

Kymanox supports clients in various stages of the product lifecycle, including post-market configuration changes. Feel free to reach out to see how we can help you develop a human factors strategy for your design changes. We are proud to support medical device and pharmaceutical companies improving healthcare worldwide through innovative technologies!


[1] Applying Human Factors and Usability Engineering to Medical Devices. FDA Final Guidance. February  2016.

[2] Human Factors Studies and Related Clinical Study Considerations in Combination Product Design and Development. FDA Draft Guidance. February 2016.

[3] AAMI TIR59:2017 Integrating human factors into design controls.

[4] AAMI/IEC TIR62366-2: 2016 Medical devices – Part 2: Guidance on the application of usability engineering to medical devices.