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There are a variety of issues that tend to recur in the life of a user interface designer. I recall the first time I was asked to write performance requirements for a user interface. How should I go about deciding on an acceptable level of errors or an acceptable speed of accomplishing a standard task? How do I know whether I have improved an interface design enough? Of the many problems that need fixing, which ones should take priority? How do I even know whether improving the user interface of a product is going to have an impact on sales? At one company, we sold usability so successfully one of the business units declared they wanted to label each product with a “usability seal of approval.” How would one go about determining when to award such a seal?

Over the years I have worked with colleagues at Ameritech (where the work began), US WEST Advanced Technologies, and most recently Sapient to create a tool that has helped in dealing with some of these questions. The tool that we developed is called the USE Questionnaire. USE stands for Usefulness, Satisfaction, and Ease of use. These are the three dimensions that emerged most strongly in the early development of the USE Questionnaire. For many applications, Usability appears to consist of Usefulness and Ease of Use, and Usefulness and Ease of Use are correlated. Each factor in turn drives user satisfaction and frequency of use. Users appear to have a good sense of what is usable and what is not, and can apply their internal metrics across domains.