A medical device may work perfectly from a technical point of view, but that does not always mean it can be used safely. An infusion pump, for example, must not only deliver the correct amount of medication. The healthcare professional must also be able to set the correct dose. Similarly, a working alarm system is not enough. The user needs to notice the alarm, understand what it means, and know how to respond. This is where usability engineering comes in.
In medical devices, usability is not simply about making a product easy to use or ensuring that users are satisfied with it. The main goal is to identify potential use errors, understand why they happen, and reduce risks that could affect patient safety as much as possible.
So, what methods are used in usability engineering? How do user research, task analysis, and usability testing work together?
When we think about where medical devices are used, it becomes clear that users do not always work under ideal conditions. Several alarms may sound at the same time in an intensive care unit. Healthcare professionals may be under time pressure in an operating room. A device used at home may be operated by a patient with no medical training. Under these conditions, even a small design detail can make a significant difference. For example, two similar-looking connectors may be confused, a complicated menu may lead to an incorrect dose selection, or an unclear warning may be overlooked. These situations can result in serious use errors. This is why usability engineering should not be seen as just another test performed at the end of product development.
Usability engineering should be part of the design process from the very beginning.
This approach is valuable not only for safety but also for the efficiency of product development. Finding usability problems early can help avoid costly design changes later. A clearer user interface can also reduce training needs, lower technical support requests, and make the device easier to use correctly.
Good Design Starts with Understanding the User
Before designing a medical device, there is one important question to answer:
Who will use this device, where will they use it, and under what conditions?
The Use Specification defined in EN 62366-1 helps manufacturers answer these questions systematically. However, understanding the user involves more than simply identifying whether the device will be used by a doctor, nurse, or patient. The user's experience, physical and cognitive abilities, use environment, and tasks should also be considered. Different research methods can help collect this information.
Observing Users in Their Real Environment
One of the best ways to understand how people use a device is to observe them in their actual working environment. For example, when evaluating a device used in intensive care, checking whether the screen is readable may not be enough. Lighting, background noise, alarms from other devices, and the healthcare professional's workload can all affect how the device is used.
This method is known as Contextual Inquiry and Observation. Users may not always notice the difficulties they experience during their daily work, or they may forget to mention them during interviews. Direct observation can help identify these hidden problems.
Talking to Users
Interviews and questionnaires are also useful ways to collect information. Users can be asked which tasks they find difficult, what problems they have experienced before, and what they expect from the device. The goal is not simply to learn what users like or dislike. It is also important to understand how they think the device works and how they make decisions while using it.
After all, a sequence of steps that seems perfectly logical to a designer may not be equally clear to the person using the device.
Learning from Experts
Not every usability assessment requires a working prototype. Clinical specialists, experienced users, and human factors experts can identify important issues during the early stages of design. For example, an expert reviewing an initial interface design may notice that a critical warning is not clearly visible or that the order of certain steps could confuse users. Identifying these problems early can help prevent more serious issues later in development.
How Do Users Interact with the Device? The Importance of Task Analysis
Once we understand who the users are and where they will use the device, the next step is to examine what they need to do with it.
One method used for this is Task Analysis.
Task analysis breaks down an activity into smaller, more manageable steps from the user's perspective. Even a task that appears simple may involve several opportunities for use error. A user may select the wrong parameter, skip a verification step, or misunderstand information displayed on the screen. The purpose of task analysis is to identify these possibilities before they lead to problems.
Function Analysis also plays a role here. It helps determine which activities should be performed by the user and which should be handled automatically by the device.
For example, instead of relying entirely on the user to recognize an unsafe dose, the device could include a built-in dose limit. This type of design decision can help reduce use-related risks.
Preventing Use Errors: Are Warnings Always Enough?
One of the most important parts of usability engineering is understanding how to prevent use errors. Sometimes an error happens because the user performs an incorrect action. In other cases, the user forgets or skips a necessary step. For example, connecting a tube to the wrong port is a use error. Forgetting an essential preparation step is another.
So, how can these risks be reduced?
ISO 14971 follows a risk control hierarchy that gives priority to certain measures. The first preference is to eliminate or reduce the risk through design whenever possible. For example, a connector designed to physically prevent an incorrect connection provides stronger risk control than simply adding a warning that says, "Do not connect incorrectly." The second approach is to include protective measures within the device. These may include software-controlled dose limits, locking mechanisms, or systems that prevent an operation from continuing under unsafe conditions.
The final approach is to provide information for safety, such as instructions for use, labels, and warnings. There is an important point to remember:
Adding another warning to the instructions for use is not always the best solution to a usability problem.
Especially in busy clinical environments, we cannot assume that users will read every warning or remember every instruction. Good usability engineering therefore aims to create a design that supports correct use, rather than relying only on users to avoid mistakes.
Formative Evaluation: Finding Problems During the Design Process
There is no need to wait until a medical device is fully developed before evaluating its usability. In fact, one of the greatest benefits of usability engineering is the opportunity to identify problems while the design can still be changed. This is the purpose of Formative Evaluation.
Different methods can be used at this stage.
Heuristic Analysis
- Human factors or usability experts review the user interface against established design and usability principles.
- They assess aspects such as consistency between screens, visibility of information, feedback provided to users, and elements that may cause confusion.
- This method can help identify design problems before testing with actual users.
Cognitive Walkthrough
- In this method, experts review each step from the perspective of a user, particularly someone using the device for the first time.
For example:
"Will the user understand what to do at this stage?"
"Will they be able to find the correct option easily?"
"Will they know whether their action was successful?"
These questions help assess how clear and understandable the interface is.
Formative Testing with Users
Expert reviews are valuable, but observing real users can reveal different types of problems. For this reason, usability tests may be carried out with participants who represent the intended user groups. During testing, observers look at which steps users find difficult, what information they misunderstand, and whether they perform any actions differently than expected.
The findings are then used to improve the design. If necessary, the evaluation can be repeated after changes have been made. This is the real value of formative evaluation: the goal is not to prove that the design works, but to identify problems that can be addressed to make it safer.
Summative Evaluation: Can the Device Really Be Used Safely?
Once the design and development process is complete, a different question needs to be answered:
Can the intended users operate the device under the expected conditions of use without unacceptable use-related risks?
This is evaluated through Summative Evaluation. Under EN 62366-1, summative evaluation focuses particularly on Hazard-Related Use Scenarios.
The tests should represent actual use conditions as closely as appropriate. For example, when evaluating a device intended for an operating room, relevant environmental conditions and user interactions may need to be considered. In some studies, anatomical models or manikins may be used to simulate clinical procedures. The goal is not simply to see whether users can complete a task. It is equally important to observe how they perform the task, where they experience difficulties, and whether their actions could affect safety.
If No Use Error Occurs, Does That Mean Everything Is Fine?
Not always.
A user may be about to perform an incorrect action but notice the mistake and correct it at the last moment. These situations are known as close calls. For example, a user may prepare to use an injection pen in the wrong orientation but correct it just before the injection. Although no actual use error occurs, this behavior may indicate that the design could mislead users. For this reason, usability testing should record not only actual use errors but also close calls and difficulties experienced during use.
What Should Be Done When Use Errors Are Identified?
Finding a use error during a usability test does not automatically mean that the study has failed. What matters is understanding why the error happened and evaluating its potential impact on safety. Did the user misread the information on the screen? Did they apply habits learned from another device? Or was the sequence of actions unclear? Answering these questions helps identify the underlying cause of the error.
The findings are then linked to the risk management process established under ISO 14971.
Potential harms, existing risk control measures, and the need for further improvements are evaluated. If necessary, design changes are made, and their effectiveness is assessed using appropriate methods. Therefore, the outcome of a usability test is much more than a simple pass-or-fail result. It provides valuable technical evidence that supports both design decisions and risk management activities.
Which Usability Method Should Be Used, and When?
Not every medical device requires exactly the same usability engineering methods.
A device intended for home use and one used in an operating room may have very different users, environments, and potential use errors. The methods should therefore be selected based on the device's characteristics and its use-related risks.
In general, the process includes:
- User Research: Understanding the intended users, use environments, and user needs.
- Task and Function Analysis: Identifying user activities, task sequences, and potential use errors.
- Expert Reviews: Identifying possible interface problems during the early design stages.
- Formative Evaluation: Improving the design and reducing use-related problems through repeated assessments.
- Summative Evaluation: Evaluating the final user interface, particularly in relation to hazard-related use scenarios.
The results of these activities are documented in the Usability Engineering File (UEF), ensuring traceability throughout the process.
Conclusion: Usability Is More Than a Test
When we talk about usability engineering in medical devices, the first thing that often comes to mind is testing with users.
But testing is only one part of the process. Understanding users, evaluating use environments, analyzing tasks, identifying potential use errors, and improving the design based on these findings are all essential parts of usability engineering. EN 62366-1 provides a structured framework for this process, while its connection with ISO 14971 ensures that use-related risks are addressed as part of the overall risk management process. IEC/TR 62366-2 also provides practical guidance on applying usability engineering methods.
Ultimately, the goal is not simply to prepare documentation that meets the requirements of the standards.
The real goal is to develop safer medical devices by considering how people actually behave and how devices are used in real-life situations.
Because the safety of a medical device depends not only on what it can do, but also on how people use it.
