Simon Johnson and Martina Schell, two of Flow's user experience consultants, recently ran a presentation and discussion about personas for the Usability Professionals Association. A really interesting question came up, which we think is worth discussing more, here on the blog:

How can I be sure that my entire user base is represented by just a few personas, when I have 5 million users scattered around the world?

Quick personas refresher

Personas are a key tool in the user-centred design toolkit. They help design teams to reach consensus about who they are really creating a product for, and to generate and sanity-check new feature ideas. Personas are fictional characters, defined in some detail: names, faces, habits, personalities. The idea is to generate as few of them as possible - ideally just one or two.

To find out more about personas, try:

• Cooper design, persona pioneers
• Wikipedia page
• Book: The Persona Lifecycle

2 personas vs 5 million users

So - user-centred design teams boil down their knowledge of their user base to a few personas. But can you really represent the need of 5 million diverse customers this way?

Answer 1: It's the best way we know

The point of personas is to reduce your user audience to a small and manageable set in order to provide a useful design tool to your designers. Designers are humans and can only handle a finite amount of information at a time (they unconsciously disregard the rest - see Christopher Alexander for more on this).

Sometimes, a customer's behaviour won't be represented in the persona set. Maybe she is the black sheep of your users. So be it. Personas are there to represent most of your users. They are based on research with a range of people from your target audience. They are a practical way of telling your team who they are designing for - because 5 million people is too many to consider at any one time. Missing out on designing for particular user behaviour is a risk, but it's a much smaller risk that designing without personas at all.

If you choose not to use personas, what are the alternatives? Designing for yourself (one, rather unrepresentative user), designing from a technology-led feature list, or designing from an overwhelming and impersonal collection of data. The odds for overall success are MUCH greater with personas than without.

Answer 2: Define the user base by its edges

You do not have to ensure that every real life user you ever encounter fits neatly into the persona set you create. Almost every one will not fit. But their behaviours will probably be represented throughout all of the set of personas - one behaviour in 'Ann', another in 'Paul' and another again in 'Stephanie'.

The trick for representing a large user base with a small persona set is to choose personas who represent the biggest challenges to the system. If you choose personas are to represent the users who are the hardest to satisfy, while capturing a reasonable subset of the average user's needs as well, you'll set yourself a meaningful design goal. Think of personas as a complex venn diagram of needs. If you focus on the average users, you only get the center of the diagram. But if you focus on the reasonable extremes, you get the outer rings of the diagram as well as the overlapping middle.

Answer 3: Don't try to design for everyone

Solutions designed for everyone are usually not particularly good for anyone. To design for everyone, you'll need to make a system that caters for opposite needs and expectations at every point in the interface - because your infinite user base want an infinite variety of options. At every point the product will rely on the user to completely decide and define what they want to do, and this will make it impossibly hard work to use - useless, in fact.

On a less philosophical level, products with a broad taregt audience can find it increasingly difficult to retain customers. Any competitor coming along with a tightly defined, easy-to use product will steal a proportion of your braod user base - because their offering will that proportion's needs far better than yours can. More competitors can cater for other niches - and soon your entire user base has been fragmented and enticed away to narrow products that better suit their individual needs.

Narrow your potential usebase, but make sure you really satisfy their needs. That's a recipe for a well differentiated product, and loyal customers.