What
is usability? How, when, and where can you improve it? Why should
you care?
By Jakob Nielsen
This is the article to give to your boss or anyone else who doesn't
have much time, but needs to know the basic usability facts. It
covers the following about usability:
What
Usability is a quality attribute that assesses
how easy user interfaces are to use. The word "usability"
also refers to methods for improving ease-of-use during the design
process.
Usability has five quality components:
- Learnability: How easy is it for users to
accomplish basic tasks the first time they encounter the design?
- Efficiency: Once users have learned the design, how quickly
can they perform tasks?
- Memorability: When users return to the design after a period
of not using it, how easily can they reestablish proficiency?
- Errors: How many errors do users make, how severe are these
errors, and how easily can they recover from the errors?
- Satisfaction: How pleasant is it to use the design?
There are many other important quality attributes. A key one is
utility, which refers to the design's functionality: Does it do
what users need? Usability and utility are equally important: It
matters little that something is easy if it's not what you want.
It's also no good if the system can hypothetically do what you want,
but you can't make it happen because the user interface is too difficult.
To study a design's utility, you can use the same user research
methods that improve usability.
<back to top>
Why
On the Web, usability is a necessary condition for survival. If
a website is difficult to use, people leave. If the homepage fails
to clearly state what a company offers and what users can do on
the site, people leave. If users get lost on a website, they leave.
If a website's information is hard to read or doesn't answer users'
key questions, they leave. Note a pattern here? There's no such
thing as a user reading a website manual or otherwise spending much
time trying to figure out an interface. There are plenty of other
websites available; leaving is the first line of defense when users
encounter a difficulty.
The first law of e-commerce is that if users cannot find the product,
they cannot buy it either.
For intranets, usability is a matter of employee productivity.
Time users waste being lost on your intranet or pondering difficult
instructions is money you waste by paying them to be at work without
getting work done.
Current best practices call for spending about 10% of a design
project's budget on usability. On average, this will more than double
a website's desired quality metrics and slightly less than double
an intranet's quality metrics. For software and physical products,
the improvements are typically smaller -- but still substantial
-- when you emphasize usability in the design process.
For internal design projects, think of doubling usability as cutting
training budgets in half and doubling the number of transactions
employees perform per hour. For external designs, think of doubling
sales, doubling the number of registered users or customer leads,
or doubling whatever other desired goal motivated your design project.
<back to top>
How
There are many methods for studying usability, but the most basic
and useful is user testing, which has three components:
Get hold of some representative users, such as customers for an
e-commerce site or employees for an intranet (in the latter case,
they should work outside your department).
Ask the users to perform representative tasks with the design.
Observe what the users do, where they succeed, and where they have
difficulties with the user interface. Shut up and let the users
do the talking.
It's important to test users individually and let them solve any
problems on their own. If you help them or direct their attention
to any particular part of the screen, you have contaminated the
test results.
To identify a design's most important usability problems, testing
five users is typically enough. Rather than run a big, expensive
study, it's a better use of resources to run many small tests and
revise the design between each one so you can fix the usability
flaws as you identify them. Iterative design is the best way to
increase the quality of user experience. The more versions and interface
ideas you test with users, the better.
User testing is different from focus groups, which are a poor way
of evaluating design usability. Focus groups have a place in market
research, but to evaluate interaction designs you must closely observe
individual users as they perform tasks with the user interface.
Listening to what people say is misleading: you have to watch what
they actually do.
<back to top>
When
Usability plays a role in each stage of the design process. The
resulting need for multiple studies is one reason I recommend making
individual studies fast and cheap. Here are the main steps:
Before starting the new design, test the old design to identify
the good parts that you should keep or emphasize, and the bad parts
that give users trouble.
Unless you're working on an intranet, test your competitors' designs
to get cheap data on a range of alternative interfaces that have
similar features to your own. (If you work on an intranet, read
the intranet design annuals to learn from other designs.)
Conduct a field study to see how users behave in their natural habitat.
Make paper prototypes of one or more new design ideas and test them.
The less time you invest in these design ideas the better, because
you'll need to change them all based on the test results.
Refine the design ideas that test best through multiple iterations,
gradually moving from low-fidelity prototyping to high-fidelity
representations that run on the computer. Test each iteration.
Inspect the design relative to established usability guidelines,
whether from your own earlier studies or published research.
Once you decide on and implement the final design, test it again.
Subtle usability problems always creep in during implementation.
Don't defer user testing until you have a fully implemented design.
If you do, it will be impossible to fix the vast majority of the
critical usability problems that the test uncovers. Many of these
problems are likely to be structural, and fixing them would require
major rearchitecting.
The only way to a high-quality user experience is to start user
testing early in the design process and to keep testing every step
of the way.
<back to top>
Where
If you run at least one user study per week, it's worth building
a dedicated usability laboratory. For most companies, however, it's
fine to conduct tests in a conference room or an office -- as long
as you can close the door to keep out distractions. What matters
is that you get hold of real users and sit with them while they
use the design. A notepad is the only equipment you need.
<back to top>
Source: http://www.useit.com/alertbox/20030825.html |
