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Including different users opens up new perspectives

How the fear of edge cases kills ideas

10 min readJan 14, 2021


Why we need to implement inclusive design methods in our innovation process in order to create meaningful products for real people.

One word that is sure to slip into conversations about inclusive design every now and then is the term ‘normal’. In the context of user experience, we use it to draw the line between interactions that seem common and those that rely on certain features like ones that support accessibility. Often, we hear it when talking about users of interest in distinction to so-called ‘edge cases’.

‘Normal’ is a term we rarely ever think about as it is so deeply rooted in our everyday language that its meaning seems solid to us, like a condition determined by laws of nature. For the most part, we don’t second-guess it, but if you were to ask people what kind of measurement parameter ‘normality’ is, depending on the context, it would lead to a whole variety of answers. That is because, in contrast to how we treat the term, it is actually abstract, its meaning volatile.

The history of normality

So what is it we talk about when we drop the word ‘normal’? Originally, it is a mathematical term that wasn’t part of our everyday language until the 19th century. To understand what it means to us today, especially as designers, we need to travel back in history, 231 years to be precise, and meet King Louis XVI of France. He faced a very unpleasant inconvenience at the time, namely a revolution.

He didn’t live to see it, but the French revolution was one of the most impactful events in history. Its influence let a wave of political change sweep over Europe, including the establishment of constitutional monarchies and, often overlooked, the formation of large-scale bureaucracies.

For the first time ever, national states started to systematically collect masses of data on their citizens.

An image of Adolphe Quetelet.
Adolphe Quetelet

Particularly interested in these huge chunks of human data, Adolphe Quetelet, a Belgian astronomer and mathematician, started to survey the medical data of about 5700 British soldiers. During the course of his studies, he calculated the sum of their body heights and divided it by their number. That made Quetelet the first person in history to ever calculate the average of a human trait.

To grasp his line of thinking, we experimented a little and did the same with the heights of all 26 employees at DAYONE. It told us, that to average, an employee at our design studio is 177 centimeters tall. Then we thought about what that number actually means.

Is it some kind of forecast for the to-be-expected height of the next designer to join our team? Could we see it as the representative height of all our designers? Actually, we realized, not a single one of the individuals that we measured was 177 centimeters tall in reality. There was certainly room for interpretation of the number, and that starkly contrasted how specific it first seemed. The more people look at that number, the more opinions on its meaning will emerge, each influenced by the specific framing and biases of the person thinking it through.

As Quetelet thought about the average height of British soldiers though, he came to a conclusion that was heavily influenced by his line of thinking as a mathematician. He discovered that the heights of the soldiers were similar to a Gaussian normal distribution.

Thus, in a nonreflective moment of deep misunderstanding, Quetelet came to the following interpretation: The closer the measurement of an actual individual was to the average of the distribution, namely its mathematical normal value, the closer the individual soldier would be to its model: the one perfect and best soldier determined by laws of nature.

In the following years, Quetelet extended his findings to society as a whole. In his deeply inhumane interpretations, he saw the average as a method to measure the degree of ‘abnormality’ of a person, and stated deformity and illnesses as deviations from the ideal. He also used his findings as a means to justify his definition of a perfect society.

Quetelets conclusions had a massive impact on the relatively new field of social sciences that were established in the course of the 19th century. Central figures of world history like Florence Nightingale and Karl Marx invoked Quetelets findings in their own work. Like that, over the course of the following decades, categorizing human traits by stereotypes was validated in the name of science.

It is important to stress that Quetelet’s mathematical findings first and foremost stand on neutral ground. Just like our attempt to infer meaning into the average height of the DAYONE employees, the interpretive framework he used should be handled with criticism and doubt.

Designing for real people

Todd Rose explains in his book “The End of Average” how the heritage of Quetelet’s work still has an implicit impact on the thought patterns we all are subject to today.

We are taught to believe that we can make meaningful assumptions about an individual if we know the traits of the average member of the societal group they belong to.

In this sense, we still talk about ‘neurotic personality types’, ‘type A personalities’ or attest someone a ’typical leadership personality’.

These implicit thought patterns explain why, when designers work with methods like personas, they put a lot of time and work into making the whole thing a perfect stereotype to represent a large group of individuals.

Unfortunately, these individuals are very likely to have entirely different needs in reality, just like the average height of the DAYONE employees does not, in fact, represent but a single individual in our lines. If we were to match our designs to these stereotypes, they would likely fail the test of reality. Just imagine the back pain it would cause the majority of us if every single desk setup in our office was designed fixed to match the height of a 177cm tall individual.

Consequently, this approach robs us of the most interesting insights that we may have collected during qualitative research: Quotes, observations, activities and interactions of actual people.

This is why, in innovation processes like Design Thinking, qualitative research methods that focus on extreme users are always given a lot of room to invoke inspiration for change and innovation.

Personally, I like to think about this as ’inductive design’. Induction describes the scientific process of deriving universally valid theories from closely observing individual cases. With the means of qualitative research, we find inspiration in the needs of individuals and use them to push for innovations that are useful to many.

The opposite way of reasoning is called ‘deduction’. Here, established scientific theories are applied to draw conclusions on the individual case, like Quetelet tried to. As designers, we generally apply this line of thinking when using methods of quantitative research. These are of course highly effective in other scenarios. We can use them to assess the performance of established services for instance, and find out where to start looking into problems more in-depth.

As designers, we need to be highly aware of the problem space we are working in. The choice of whether we use qualitative or quantitative research should be made consciously. We need to ask ourselves what our direction of thinking and reasoning should be before we make a decision on which research methods to apply.

An infographic that shows the described direction of reasoning in both deductive and inductive thought processes.
An infographic that shows the described direction of reasoning in both deductive and inductive thought processes.

Identifying inclusive design methods

To make use of the potential of qualitative research in innovation processes, we need to find ways to synthesize large amounts heterogeneous data (like quotes, observations and more) without watering it down by cramming it into stereotypes.

Hence, you should look out for methods that manage to accumulate manifold and even diverging needs of your users. Great instances are the Value Proposition Canvas for synthesis or the Rainbow Spreadsheet for data visualization. This, however, is only the beginning. You could also go a step further and focus on learning from extreme users from the very start of your research phase.

Scaling inclusive design

When I was working on a project that focused on shared office spaces, we looked into what people need from co-working spaces. We interviewed what you would call ‘normal’ users, like startup entrepreneurs or freelancers, as well as extreme users. Thus, we talked to people who are freelancing because they have chronic health issues and need a lot of flexibility in their work life.

Nearly all of the interviewees stated networking as an important benefit when renting desks at shared office spaces. This need was particularly obvious when talking to the extreme users however, because they generally have more constraints that keep them from networking efficiently.

As we proceeded in our design process, we decided to push for a solution that would focus on benefitting these extreme users. This forced us to find and tackle the root of the problem space. If we could create a solution for people who are excluded from networking in existing work environments, of course that solution would ultimately benefit all users and consequently lead to something new.

It is a common misconception among product teams that inclusive design is difficult to scale. It is a needless fear that can keep us from discovering great solutions. In reality, learning from and designing for extreme users, or so-called ‘edge cases’, has brought us many of the designs we couldn’t imagine our lives without today.

Curb cuts

In this context, you may have already heard of the “curb cut effect”. Following the protests of the disability rights movement in the USA during the 1960s, curb cuts were introduced to make it easier for people using wheel chairs to get across streets. Later, it turned out that this hard-won change was actually helpful to a wide variety of users, like those who rode a bicycle, construction workers who transported heavy materials, or parents with buggies.


The so-called ‘father of the internet’, Vint Cerf, was inspired to promote a means of long distance communication that didn’t require the ability to hear, as he and his wife are hearing impaired themselves. Thus, he invented the first e-mail protocol.


In 2005, Apple acquired a company called ‘FingerWorks’ that specialized in designing accessible computer interfaces for people with motor impairments. The engineers at Apple made use of that technology to create an easy to use touch screen interface. Little over two years later, the company launched the iPhone.

There are many more of these examples to be found throughout history. We’re part of these stories whenever we watch a video with automatic subtitles in crammed subways instead of letting everyone in on what we are watching, or when we’re welcomed by automatic doors with our hands full of groceries.


An infographic that shows how insights generated from studying edge cases can be used to influence a bigger group of users.
An infographic that shows how insights generated from studying edge cases can benefit a larger group of users.

All of these stories have in common that they dissolve the artificial boundary that we create between ‘normal’ interactions and so-called ‘edge-cases’, and integrate them to create inclusive designs that benefit a vast variety of users.

In ultimate consequence, this means that disabilities are no personal health condition, like the WHO suggests, but really a complex phenomenon describing the accumulation of mismatched interactions between an individual and the society they live in. This point of view opens up a whole field of possibilities for designers, but it also clearly makes inclusion part of our responsibility as we shape interactions that have a meaningful impact on society.

3 tips to design inclusively

  1. Lose your fear of edge cases. Looking at extreme users can help you discover needs that are subconsciously affecting all users. Ultimately, it will lead you to create inclusive solutions that benefit all users.
  2. Be conscious of the methods that you apply. Second guess established methods, too. Do they lead to true insight or inhibit you from finding the root of the problem by promoting stereotypes? Likewise, keep an eye out for design methods that help you include diverse needs in your design process.
  3. Recruit a wider variety of people in your research. To get started, try and include someone in your next research who you clearly think isn’t part of the group of core users you try to reach. It should be someone who doesn’t look like, think or act like them. Be mindful of your thought patterns and consciously investigate an ‘edge case’. Be curious about the things that you may find. It might just be a new perspective.

Written by Miriam Zils, UX Designer at DAYONE

Miriam Zils

About the author

Miriam has a background in visual design. At DAYONE, she transitioned into the field of UX when she noticed how much she enjoys tackling design problems systemically. During her studies at Hasso Plattner Institute, she deepened her understandings of Design Thinking, and connects these processes to the notions of inclusive design.

What else does she like? Miriam can get lost in graphic novels, digital art and creative writing challenges for days…


The thoughts and ideas in this article are to a great extent inspired by two books that we highly recommend on the subject of Inclusive Design:

Mismatch: How Inclusion Shapes Design (Simplicity: Design, Technology, Business, Life) by Kat Holmes

The End of Average: How We Succeed in a World That Values Sameness by Todd Rose



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A studio for service and digital product design — we partner with organizations on their way to a user-centered tech company.