Every time a new platform comes along--first DOS, then Windows, then the Web, and now smartphones and tablets--developers have to struggle for a while to get by without the tools they had become familiar with on the earlier platform. Eventually, however, toolmakers come up with application programming interfaces (APIs) and shortcuts and development speeds up again. The same is true for usability tools and techniques, although usability experts aren’t waiting for software tools, but rather for information about what makes an app (in the case of smartphones) usable or not.

This is one of the first papers on usability for smartphones. Choi and Lee hypothesize that simplicity is the hook on which all smartphone usability hangs. They use six characteristics to define simplicity: reduction, organization, component complexity, coordinative complexity, dynamic complexity, and visual aesthetics. Reduction means that menus, buttons, functions, and information are reduced to the minimum needed. Organization refers to well-ordered items on the interface. Component complexity is “the perceived degree of visual density in text, images, icons, and layouts.” Coordinative complexity is the perceived degree of logical connection between interface items and their functions. Dynamic complexity is the perceived degree of predictability in the interface--in other words, when I press a button, I get what I expect. Visual aesthetics is defined as “neat, modern, and balanced,” which is based on Moshagen and Thielsch’s visual aesthetics for Web site inventory (VisAWI) scale [1].

The authors surveyed 205 smartphone users about these characteristics and about overall user satisfaction. They found that the strongest component of perceived simplicity was visual simplicity, but that all the components were important to user satisfaction. Component complexity had the lowest degree of influence; the authors hypothesize that this is because less-experienced smartphone users find many components confusing, while more-experienced users “overcome the cognitive load and feel density less.”

So we have at least one answer to the question of what makes smartphone apps usable--simplicity. Next, someone needs to run some actual usability tests against Choi and Lee’s recommendations and see how well they hold up in the real world. Hopefully this is the authors’ next project.