1.5 Think About It

No aviation firm would design and build a new jet airliner without first doing an engineering analysis that predicted the plane's performance. The cost of construction and the risk of failure are too high. Similarly, the costs of building a complete user interface and testing it with enough users to reveal all its major problems are unacceptably high. Although interface design hasn't yet reached the level of sophistication of aircraft engineering, there are several structured approaches you can take to discover the strengths and weakness of an interface before building it.

One method is to count keystrokes and mental operations (decisions) for the tasks the design is intended to support. This will allow you to estimate task times and identify tasks that take too many steps. The procedures for this approach, called GOMS analysis, along with average times for things like decisions, keystrokes, mouse movements, etc. have been developed in considerable detail. We'll summarize the method later in the book.

Another method is to use a technique called the cognitive walkthrough to spot places in the design where users might make mistakes. Like GOMS modelling, the cognitive walkthrough analyzes users' interactions with the interface as they perform specific tasks. We'll also explain how to do cognitive walkthroughs later in the book.