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Usability: Intro
Prof. Dr. Christian Johner
Usability Engineers
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veröffentlicht am 14.09.17
The term "usability" is becoming overused and misunderstood at the same time. In this video training, you will get to know how the term is defined, why you have to take usability into account, when developing medical devices, and the trends you should be aware of – also with respect to audits.
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The term "usability" is becoming overused and misunderstood at the same time.


In this video training, you will get to know how the term is defined, why you have to take usability into account, when developing medical devices, and the trends you should be aware of – also with respect to audits.


FDA states that the term "usability" is so frequently confused with design, that it should be replaced by "human factors engineering".

In fact, usability is not about nice colors, shadows or fancy design elements. Usability is defined by ISO 9241 as “The extent to which a product can be used by specified users, to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use”. I.e. usability is about achieving targets – fast and without unnecessary effort.

But already IEC 62366 starts messing with this clear definition. According to IEC 62366, usability is a “characteristic of the user interface, that establishes effectiveness, efficiency, ease of user learning and user satisfaction”. Again, we find effectiveness, efficiency and satisfaction. But important aspects, such as specified users and the specified context are missing. On the other hand, “ease of user learning” is added.


This is a misconception. “Ease of user learning” or “suitability for learning” is one of the seven dialogue principles. If a product is designed according to these principles, it will be usable. That means it will help the users:


  • to actually reach their targets at all – effectiveness –,
  • to reach these targets without any unnecessary steps – efficiency -
  • and without being unsatisfied.

The dialogue principles are preconditions to achieve usability; they are not aspects of the usability itself.

User experience

Another term has been frequently confused with usability, in particular in the hype phase of certain Apple products. There was a notion, that these emotions are caused by the extraordinary usability of these devices. We have to be more precise:

Usability is a characteristic of a product, a user can only experience during the usage of the product. The anticipated use, that means what the user expects the product to be like, and the perceptions after the use, are part of the user experience. In other words, usability is just a part of the overall user experience.


Medical device manufacturers meanwhile understand, that usability is an important factor for developing successful products. The customers’ awareness and attitude to demand usable products has changed over the last years.

Manufacturers frequently complain about customers not knowing what they want. However, it is not the customers’ task, to identify their own needs.


Already Henry Ford said: “If I'd asked people what they wanted, they would have said: a faster horse.”


As companies fail to identify the actual stakeholder requirements, they waste a substantial amount of time and money, implementing functionality that nobody needs. But products without the required functionality are not usable. Usability – if you remember – is the extent to which users achieve targets… Usability and requirements engineering are two sides of one coin.


The Standish group examined this more systematically, and found out, that two out of three projects fail to reach targets in time and budget, due to inadequate requirement engineering: User involvement and a clear statement of requirements are the preconditions for successful projects.

Overview: Targets

As you might have realized, companies waste resources, time and money. They could significantly reduce costs, by identifying the stakeholder requirements right away, and not iteratively trying to converge these requirements.

The next and obvious reason for caring about usability, is just to fulfill the legal requirements. In the next training, you will learn what these requirements are in Europe and in the US.

And these requirements are about managing risks.


In the past, the main focus of risk management was the product itself. Any component was analyzed. Also the standards like IEC 60601-1 address in particular the devices. Meanwhile, it is understood, that the interaction of users causes risks, too. The way users enter data or perceive the output of systems, causes risks as well. So we may not only focus on the device interfaces towards the patients, but also on the in- and outputs to and from users, and on the context of use.


Just to give you some examples where usability actually caused harm to patients.


  • There was a system with a font, that displayed the number one and the letter “l” in the same way.
  • As a system did not show the units of measure; a physician entered a lab value in a different unit than the system expected. Therefore these values were not marked as out of range. However, nursing staff relied on these markers.
  • Wrong default values or scales were misleading.
  • A device in an ICU did not show the alarm limits. So the staff was not aware that these limits were turned off. The necessary alarm was never raised.
  • Users of a clinical information system could leave screens, without saving data. So data got lost. But this data would have been important for further treatment.
  • A heart-lung machine had a red and blue switch. A physician did not know what to select. He decided on blue, as this seems to be less critical than red. Unfortunately, blue did not mean uncritical, but venous blood and red meant arterial blood. The baby died.
  • Another system allowed users to prescribe drugs for “tomorrow”, for the next day, without having to enter the next day’s date. This went well, until a treatment took longer than midnight. The physician was not aware of that. The drug prescription was for a day too late.


We would like to point out two things:

First: The examples show, that lacking usability is much more than helping the users to properly read. Think of the misleading fonts, think of bad contrast ratios or fonts that are too small. All these cause problems with cognition.

However, at least as important is that users do not only read what is displayed correctly, but also understand the meaning. Different mental models of manufacturers and users cause problems with perception.

Context of use

The second point we would like you to be aware of, is the context of use. A product is not per se usable or unusable. It is only usable or unusable in a specific context. This context includes user characteristics, such as age, education, language skills or physical abilities. Think of color blindness.

This context includes the physical environment, too: Temperature or brightness for example, might strongly influence whether users wear gloves, or are blinded.

Also the stress level is part of this context.

All these aspects are ideally described in the intended use description. We encourage you to listen to our dedicated video trainings on how to document the intended use.

For premium members, there are templates available for download, that show examples of how to document the context of use.


Indeed, medical device manufacturers, but also authorities are becoming more and more aware of how important usability actually is. My colleague, Professor Stettin, reports recent numbers from the FDA: According to this authority, the second most prominent reason for recalls is software. And more than two thirds of those recalls are related to lacking usability. Consequently, audits are increasingly taking a closer look at how manufacturers address usability throughout the entire development process – and even after.

European notified bodies are slowly building up competency in this domain. Their approach is still quite formal, and for example does not really address the context of use appropriately. I’ll expect this to change pretty soon.

We are engaged in the Standard Committees, to further improve standards like IEC 62366. We have to come up with an approach to usability, which is as structured, methodical, consistent and logical, as already achieved in other processes, domains and standards.


In this very first video training, you learned about the most relevant reasons to systematically address usability: Market success, efficiency of development, regulatory compliance and risk management. We started discussing how risk management and usability relate to each other. And you heard about upcoming trends.

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