Firstly, this is not about adjusting your chair so that you're not slumped over the screen when working on a Flash prototype (although office ergonomics is a very important subject). Rather, the topic of discussion is the increasing value of ergonomics knowledge to the interaction designer. Ergonomics is necessary for 3-dimensional, tangible product design where issues of physical fit and comfort are critical. But for interaction designers in the 2-dimensional world of the display screen, ergonomics has largely been...irrelevant. For example in most cases, interfaces are designed for existing, defined hardware that are out of the control of the interaction designer. But things are changing...
The continuing convergence of digital interfaces with physical products is putting interaction designers in a position where knowledge of anthropometrics, kinesthetics, and other non-cognitive human capabilities is valuable for creating effective design solutions.
There are several trends contributing to this, including:
- The rapid proliferation of touch screen and other gestural interfaces which combine "direct" physical control with digital interface design. If you want to design for a finger, you have to know how a finger works.
- The growth of ubiquitous computing leading to an increased range of scale and form factor in devices that contain interfaces, from traditional computers and laptops, to kiosks, tablets, phones, interactive video walls, electronic ink and consumer appliances (to name a few). As a result, people are interacting with interfaces in range of positions and contexts that go beyond simply standing or sitting in front of a screen. So beyond fingertips, knowing how people can reasonably user their bodies to hold, view, reach and interact is valuable.
- Computing power and bandwidth across such devices now supports more complex, involved tasks such as data entry, long duration reading and gaming, all of which can lead to risks for repetitive motion injuries, or at least discomfort. Having a knowledge of the types of interactions that can cause such injuries, and how to design around them, is essential.
- An ever increasingly diverse range of end-users are gaining access to interactive devices, across age, and physical characteristics. For example, the One Laptop Per Child campaign has produced a global, kid-sized laptop. In home health care, a market of predominately elderly users, more devices contain embedded interfaces. And ADA and similar legislation requires that devices are accessible to users with a range of disabilities. In other words, you need to know your user, for it is not you - a given in interface design, a necessity in ergonomic design.
- Last, but not least - interest. Several of the factors described above are driving many interaction designers to explore and study the world of physical product design. For example, the IIT Institute of Design is hosting a "thinkering" workshop specifically to provide "an opportunity for interaction designers to get their hands dirty with electronics, soldering, and wiring, and learn how to interface hardware artifacts with virtual interactions." Just as it is important to understand the electro-mechanics of hardware, it is essential to understand the relevant mechanical attributes for the users of such hardware.
What all of these trends have in common is a growing need to accommodate human physical characteristics and constraints in the design of digital interfaces. For the most part, this skill set is not part of the experience of interaction designers. Consequently, I'm posting this first in a series of explorations on the topic of Ergonomics for Interaction Designers, or E *IxD for short.
Anthropometrics: The Building Blocks of Ergonomic Design
In any field of design there are those elements that are defined and unchangeable, and those that are malleable It is the latter in which designers specialize. For example, in interaction design, the fixed elements might include a specified screen resolution, development language and minimum type size. As you might guess, in physical product design, there are many constraints, but human physical characteristics are the most fundamental. Therefore, the most fundamental design question is, how do I design for the range of human physical constraints? For this, we turn to anthropometrics the measure of human body size and proportions.
Let's focus on one simple anthropometric variable - height. Actually, even height is not that straightforward as there are many types of height: stature (what we mean when we say height), eye height (distance from the ground to the eyes - important for display positioning), shoulder height, fingertip height (standing, with arms relaxed), and sitting elbow height, to name a few.
Suppose we are designing an interactive touch screen kiosk that will be used in an international airport terminal (like the one pictured below, via Core77). It is expected that the kiosk users will include travelers from around the world, male and female, from kids through elderly adults. While this may sound like the worst case scenario for physical design (and it is), it's also very typical. In this case we are going to focus initially on eye height because we want to set the display so that it can be viewed most easily without looking up or bending down too much. (Note that line of sight is optimally about 10 degrees below the horizontal plane.)
If we refer to anthropometric data tables, like those found in Stephen Pheasant's Bodyspace, we find quite a range in eye height, varying by nationality, age and sex. For example an average, 50th percentile Dutch man has an eye height of 1670mm, while an average, 50th percentile eight year old British girl has an eye height of 1165mm. That's over a 500mm difference, and those aren't even the most disparate populations! So how do we accommodate the diversity of physical characteristics?
Molenbroek and de Bruin discuss the various approaches that one can take to accommodating the range of anthropometric characteristics, summarized in the diagram below:
The most basic approach, if we can even call it that, is "Procrustus", which means that no attempt to accommodate the user has been made, and the user must adapt to the product, however it happened to be designed. Incidentally, this term comes from Greek Mythology, where Procrustes was fitted to a bed by sawing off his head and feet. Only slightly better is the Ego-design approach, where the designer uses his or her own body as a reference. Now every designer does this to some extent for convenience, but it should serve only as a starting reference point.
Design for the mean sounds like a good idea - find the average eye height, and the majority of users will be accommodated. False assumption - as the diagram indicates, a majority of people are excluded by relying on the mean, with only a few falling into the sweet spot in the center.
Designing for one end of the spectrum (small) or the other (tall), can work in some cases. For example, if you design a door to accommodate the tallest users, then by definition, those of shorter stature will fit as well, as clearance is a one-ended variable. But in our case, the appropriate height of a kiosk display is a two-ended issue - there is a hypothetical "too high" as well as a "too low".
Which brings us to some workable approaches. Design for adjustability means that the product can accommodate a range of users, typically through a mechanical solution. For example, a tilting, height adjustable screen, or multiple interaction stations set at different eye heights. Of course adjustability in the physical world adds cost and complexity, and can lead to unreliable products, so is not always an available solution.
In the end, the most common solution is to Design for More Types. In practice this typically means defining a population and then fitting for a reasonable range within that population. Traditionally that range spans from the smallest fifth percentile to the largest 95th percentile. This includes a very broad range of users, but purposely excludes the most extreme 10% of the population (the largest 5% and smallest 5%) - the long tail, where a small number of outlier users can account for a significant design change.
Last, but not least is the ideal - Design for All. This means that the product can fit the entire range of an anthropometric characteristic. This is technically possible as humans are not infinitely variable in any dimension.
Part 1 Takeaways:
- Knowledge of ergonomic methods and techniques is becoming a valuable skill set for interaction designers due the growing diversity of devices, users and contexts for interaction.
- Anthropometrics, the measure of the human body, is a fundamental area in ergonomics, and a starting point for understanding how to design systems that fit people.
- Among anthropometric approaches, designing for a broad range (5th to 95th percentile) is often the most practical and accomodating.
- When furniture shopping in Ancient Greece, be specific about measurements.
In Part 2 I'll discuss how to apply the anthropometrics to a real-world interaction design problem, and also discuss the added complexity of dealing with multiple anthropometric variables - like eye height and arm length, so the user can actually see and reach the screen.
comments and suggestions always welcomed...