Usability engineering for medical devices can easily become either too heavy or too thin. Some teams over-engineer simple interfaces; others under-scope complex tasks and meet surprises late. The sweet spot lies in tailoring — scaling your usability effort to real risk and context.

Before you decide how much usability work is enough, make sure the ground you stand on is solid. Tailoring decisions are only as good as the information that drives them. In practice, three key inputs form the backbone of any proportionate usability engineering approach:

1. A complete User Interface Description – What users see, touch, and interact with. This document includes displays, controls, indicators, and workflow elements.
2. A structured Use Specification – Describing who will use the device, in which environments, and under what conditions.
3. A Use-Risk Analysis – Integrating both pre-market assessments and real post-market feedback to identify hazard-related use scenarios.

Without these inputs, tailoring becomes guesswork. Teams risk scaling activities incorrectly and consequently investing heavily where it adds little value, or overlooking areas where safety and comprehension depend on more thorough evaluation. When these three foundations are sound, every subsequent tailoring decision i.e. what to test, how deeply, and why, can be made with confidence, traceability, and full alignment to IEC 62366-1 expectations.

Tip for practitioners: If any of these inputs are incomplete, treat it as an early signal. Fill the gaps first or, at minimum, record clear assumptions and follow-ups in your usability plan. This avoids surprises later and keeps your tailoring defensible in audits.

Once your foundation is in place, the next step is to decide where to focus your effort.
A risk-based approach ensures that your usability engineering activities are proportionate, that is, neither too heavy nor too light.

In essence, tailoring means investing more where the consequences of error or misunderstanding are high, and scaling down where risk is limited and well-understood.  This mindset is deeply rooted in IEC 62366-1, which explicitly allows flexibility when justification is documented.

To make these decisions systematic, teams can define clear risk-related decision factors that help distinguish between high- and low-priority areas. In practice, two factors have proven particularly useful when evaluating usability risk:

• Severity of harm – What is the potential impact if the user makes a mistake?
• Magnitude of UI change – Does a new or modified function introduce new potential use errors?

By rating these two factors and combining the results, you gain a structured way to “grade” usability activities.
High-risk areas can then be addressed first and in more depth, while low-risk elements may require only streamlined formative evaluation or expert review.

Other influencing factors such as UI complexity, breadth of the use specification, or the presence of legacy elements also play a role in decision-making. However, these extend beyond the pure risk perspective and will be explored further in a separate article.

Tip for practitioners: Document your reasoning for each decision. Even a short note, stating why a task was considered low risk, or why a formative test was scaled up, helps maintain transparency and audit readiness.

Tailoring only becomes effective once it is made explicit.
Many teams intuitively scale their usability activities but fail to describe how and why those decisions were made. Without that traceability, flexibility can appear like inconsistency and that’s exactly what regulators want to avoid.

A well-structured User Interface Evaluation Plan (UIEP) turns tailoring into a transparent and defensible process.
It serves as the single point of reference connecting risk, rationale, and evidence.

When you create or update your UIEP, make sure it captures four essential elements:

1. Scope and rationale - Which usability activities will be performed, to what extent, and why.
2. Decision logic - How scaling choices follow from risk and context, for instance, why one task needs a full formative test while another requires only expert review.
3. Coverage rules - How user groups, use environments, and hazard-related scenarios are represented and justified.
4. Change control - How design updates trigger reassessment or retesting, and how decisions are recorded over time.

This documentation doesn’t need to be lengthy, but it must be structured and verifiable. A concise table mapping decisions to risk factors often works better than long prose.

Tip for practitioners: Treat the UIEP as a living document. Each tailoring decision should have a short, checkable rationale that can be traced back to the corresponding hazard or design change. That clarity builds confidence not only with auditors, but also within your own development team.

Once the decision framework is in place, it’s time to put tailoring into action.
Execution is where the balance between efficiency and safety becomes visible. The key principle: apply the right amount of effort for the actual risk profile.

Not every user interface requires the same depth of testing. Low-risk or well-understood elements might be covered by streamlined formative evaluations or expert reviews, especially if previous data already confirm safe and intuitive use.

By contrast, novel, complex, or high-risk interactions demand deeper formative exploration and realistic summative testing to confirm that users can perform critical tasks safely and effectively.

This proportionate approach helps avoid redundant loops and late surprises. Instead of repeating the same evaluations “just in case,” every activity has a clear purpose tied to risk, context, and learning objectives. The result: a smoother, more predictable path toward usability validation.

Tip for practitioners: Define success criteria before you start testing. A well-formulated criterion, such as “critical tasks completed without use error in ≥ 90 % of attempts”, turns each evaluation into an evidence-producing step rather than an open-ended exploration.

Tailoring usability engineering is not a one-time exercise: it’s a discipline.
Each decision about what to include, omit, or scale must remain traceable as the design evolves. When new hazards appear, workflows change, or new user groups are added, revisit your tailoring assumptions. Adjust them where necessary and keep the reasoning documented.

That continuous loop between risk, rationale, and evidence not only ensures compliance with IEC 62366-1, but also strengthens the maturity of your entire development process. Teams that maintain this traceable link tend to work more predictably, reach summative validation faster, and build stronger confidence with regulators and users alike.

Tailoring is about working smarter, not lighter.

It enables teams to focus effort where it counts most, achieving safety, efficiency, and audit readiness in one step.
When applied systematically, it transforms usability engineering from a regulatory obligation into a strategic advantage.

If you’d like to explore the practical side of tailoring, including checklists, examples, and ready-to-use templates, visit our detailed article on the USE-Ing. website.

Benedikt Janny, Senior Usability Engineer, Euro-Ergonomist, scientist, and founder, holds a PhD in engineering and has dedicated his career to advancing human-centered design in medical technology. During his research years, he focused on developing adaptive human–machine interfaces for gerontological and medical applications—work that sparked his passion for designing industrial medical products around users.

Since then, he has worked with both global corporations and MedTech startups across the fields of UX, Human Factors, and innovation, and has co-founded several ventures himself. Today, as Managing Partner of USE-Ing. GmbH, one of Europe’s leading Human Factors and Usability Engineering agencies for medical device development, he drives the integration of usability and human factors into cutting-edge MedTech innovation.

As an international speaker and university lecturer, Benedikt is deeply committed to sharing knowledge and expertise. He also contributes to standardization and professional communities—serving in the DKE committee for IEC 62366-1 and in the German UPA “Med&Health” working group—to strengthen the role of UX and Human Factors in research, education, and practice.