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How Many Usability Studies?
So far, this chapter has assumed you're doing one usability study. But how many usability studies do
you need to do for your product? For starters, plan just one study and let the results determine whether
you're comfortable that your design works or you need to redesign and then test again. Some product
teams use paper prototypes in the early stages to smoke out the show-stoppers and then plan a small
usability study or two later with the real interface to find any issues that wouldn't have come up with
paper.
Companies that do a lot of prototyping and usability testing tend to evolve into an iterative process that
uses small, frequent usability tests throughout the development cycle rather than one or two large
efforts. Following are two examples.
From the Field: Iterative Usability Testing
"Although we do a lot of usability testing, we only bring in a few users each round. On the CP
Select tool [described in
Chapter 2
], we tested five versions of the paper prototype, but we did
our first two rounds of testing with two to three users each, and they were internal users. This
works for us because our tools are highly specialized and we have ready access to domain
experts in-house. For the next three rounds, we tested with both internal and external users, but
only a couple of each. So for the whole project we worked with maybe six external users and a
dozen internal. But that was enough to see radical improvements in our design—the team was
surprised at how much easier it was for users to complete tasks in the final version.
"We also need to determine when we've done enough testing. What drives each round of testing
is how clear we are on what the problems are. The data we collect also tells us what can stay the
same. Over time, we can chart our progress by seeing how much of the design can stay the
same—we call this 'gelling.' Once a design gels, we feel comfortable going off and implementing
it, because the remaining issues tend to be minor."
By Jennifer Lymneos, The Mathworks
"On one project I did usability tests every Friday for five weeks. I started with some rough
prototypes our graphic designers had created in PhotoShop and printed them out. I sat down with
four to six users (one at a time) on a Friday and walked them through a series of 'functional'
questions (e.g., How would you use this page to do X?). I gave them markers so they could mark
up the paper screen shots as they answered my questions. I spent the following Monday and
Tuesday working my notes into design changes to apply to the PhotoShop files. In week 3 I
began to show them the screen shots on a monitor—I'd gotten what I could from paper and was
ready to switch over to doing it on a computer. By week 5 the users were looking at HTML files
rather than flat graphic files (our designers were converting the flat files to HTML during this
time). At the end of five weeks the design had stabilized to the point where I was only finding
small issues."
By Brent Mundy, Usability Specialist
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