A user is anyone who interacts with a designed intervention, or is directly or indirectly affected by its function.

Users can be defined according to the stages of a product's life cycle. Users from different user groups will perform different tasks with a product. Good design supports all those tasks, regardless of which group a user belongs.

In this section, we'll first consider how to identify and characterize user groups generally. Then we'll look more closely at the two times during our design process that we describe, refine, and verify user groups.

Users can be grouped broadly by how they use a design intervention; these categories also coincide with the stages of a product's life cycle.

Generally, every intervention has more or less the same user groups (especially from an engineering point of view):

For instance, consider an automobile.

• The end-users of the automobile are the people who will drive it.
• Mechanics are users too, although their interactions with the automobile will be very different from those of the end-users. So we treat them as a separate user group.
• Manufacturers and those directly involved in recycling the automobile at the end of its life also constitute distinct user groups based on the kinds of interactions they will likely have with the automobile.

People in each of these groups may well be characterized in very different ways: cognitive skill, physical abilities, income, training, social standing, etc. can all differ radically between user groups.

Also, each user group's characteristics will be different for different products - e.g., people who drive Rolls Royce cars are generally different from people who drive Toyota Yarises.

Very significantly, co-users are often forgotten or neglected during design. This is usually bad because they can significantly alter the situations involving the intervention.

• For instance, passengers in a car, pedestrians, and wild animals crossing streets can all be thought of as co-users.
  • If a moose gets in front of your car as you're driving down the highway at night, things may turn out very badly - for you as well as the moose.
  • Accidents can happen when passengers distract a car's driver.
  • On the other hand, passengers can also help the driver navigate, or even make them aware of dangerous situations.
  • If you have to use a rickety ladder, it might be very helpful to have a co-user hold the ladder to help stabilize it - and you.

Notice that the potential direct impact of the intervention on each user group gets smaller as you go down the list of user groups. This is only because our interest is in the intervention from the engineering point of view; things would be different if we were considering this matter from some other point of view.

This list is not exhaustive. Depending on the nature of the design imbalance you are trying to resolve with your design, some of these user groups can be safely ignored, and other groups (e.g., “installers” of equipment) will have to be added. You will have to think this through yourself for each design project.

Once you've identified all the main user groups, you now have to decide what types of people will be included in each group.

Remember that you can't design something that literally anyone can use, or make, or sell, or recycle. Each user group will exclude some individuals. The question is: which individuals should you or must you exclude? The answer will depend on the situation you're trying to address, and the product strategy that you take in your design.

To characterize each user group, you simply list relevant characteristics of the kinds of people you want to include.

• A simple point-form list is enough.
• Ideally, this list will be exhaustive, but this will rarely happen in practice.
• Make sure you're covering the most essential characteristics that are relevant to the situation you're trying to address.

It's important to choose the characteristics that most matter to the specific design situation. Some characteristics are better than others. It's informative to consider some typical beginner's mistakes to help identify what constitutes good characteristics.

The first time we consider user groups is after a situation scan. At this point, we're still trying to understand the current situation - the way things are - for the sake of understanding the context into which we'll be adding our designed interventions.

At this point of the design process, we have researched existing products, designs, and solutions. Those existing interventions were designed for specific user groups. Your job here is to try to describe the user groups by inferring their characteristics from information about the interventions themselves.

For instance, consider a Toyota Yaris and a Rolls Royce Silver Shadow. What can you infer about the various user groups just based on what you can learn about the cars themselves? Clearly, the owners of the Rolls will have more disposable income than the Yaris owners. But what else can you tell about them? What features of the car itself might tell you something about the owners? Are they young or old? Are they able-bodied or not? What level of education might you expect them to have? These are all things you can intuit - and in many cases actually find out about via the Web - and that will tell you about the kinds of users each car was designed for.

Use your background research to intuit the characteristics of each of the user groups for your project. Document those characteristics by referring to pertinent background research. At this point, you are just describing to the best of your ability the actual user groups for existing interventions. You are not deciding whether those user groups are particularly exclusionary or otherwise problematic. You're just reporting on what you've learned about existing designs.

Further into the design process - when you're defining the expectations you'll put on your own design to improve the current state of affairs - you have a chance to tweak the user group descriptions to align better with what you want to achieve with your own design.

To do this, you must have already documented some systemic flaws in existing interventions. Based on thinking about those flaws, you should be able to either (a) verify that the user group descriptions are still reasonable or (b) determine specific changes that will “improve” the user groups. Here are some examples.

Example: neglecting a significant group of disabled users. It may be that products that you researched commonly neglect people who lack sufficient mobility (perhaps due to arthritis), or a sensory lack (e.g., poor vision) to use a the products. You can start to address that by expanding the description of the end-user group to explicitly include people with arthritis or people with poor vision.

Example: an expensive but mature technology is used. Perhaps the researched products seem too costly compared to other classes of products that use similar technology. (e.g., a \$1,000 standing house lamp that uses \$2 LED technology.) In this case, the users who are excluded are those without the money to buy the lamp. You can start to address this problem by expanding the description of the end-user group to explicitly include people of lower incomes (you should specific a target for the minimum income level).

At this stage, you would update the user group descriptions, being careful to ground your justifications for changes in research you've done and facts you know about what is and what is not possible and reasonable.

In academic settings, you will likely lack the experience and resources to fully describe all the user groups. This matter is simplified here - but recognize that these allowances are made only because of the academic setting.

• End-users and co-users must be fully and appropriately characterized to “marginally meet educational expectations”¹⁾.
• Additionally, characterizing and designing for manufacturing, maintenance, and end-of-life user groups is necessary to “meet educational expectations”²⁾.
• Additionally, characterizing and designing for at least one other user group is necessary “exceed educational expectations”³⁾.

Fig. 1: Humanely dispose of bugs...

User groups are not necessarily rational, and certainly never perfect⁴⁾. The irrational nature of user groups is often manifested in their preferences for products.

Fig. 2: ...but DESTROY ALL pidgeons!

A given user is generally predictable. But groups of users can exhibit behaviours that are inconsistent. Consider the bug catcher shown here, which is used to humanely capture house pests like bugs and spiders, and then release them safely outside the house. While this is perfectly reasonable by itself, it becomes a problem in light of the pigeon-killing device that often adorns windowsills in city buildings.

The question is: how does the designer deal with the paradox of users who are happy to let spiders live but torture and kill pigeons? This kind of problem cannot be predicted, which means designers must be flexible enough to respond quickly depending on the circumstance.

You must document who the user groups are, how they are characterized, and how you expect them to want to use your design intervention. This information will be vital in subsequent stages of the design process.

It is sufficient to use extended point form, as done in the examples above. Basically, name each user group, and list their most significant characteristics. The most important thing is to capture the most significant differences between the user groups with respect to the specific design brief you are working with.

When you're revising user groups, be sure to state clearly what has changed, and why you changed it. Simply writing down an altered user group description is not enough; you must be able to defend your rationale for the alterations.

Exclusion Calculator

This tool, developed by the University of Cambridge, helps designers determine how many people are excluded from using an intervention based on common abilities and disabilities. Statistics are based on the UK population only, but it remains useful for roughly estimating exclusions in most developed nations.