How to Measure the Ergonomic Quality of User Interfaces in a Task Independent Way

The main problems of standards (e.g., ISO 9241) in the context of usability of software quality are, that they can not measure all relevant product features in a task independent way. The author presents a new approach to measuring user interface quality in a quantitative way. First, he developed a concept to describe user interfaces on a granularity level, that is detailed enough to preserve important interface characteristics, and is general enough to cover most known interface types. The author distinguishes between different types of 'interaction point'. With these kinds of interaction point several types of interface (command, menu, form-fill-in, desk-top, direct manipulation, multimedia etc) can be described. The author analysed the outcomes of three different comparative usability studies to validate the quantitative measures. The results of a published comparative usability study by someone else can be predicted. Results of six different interfaces are presented and discussed. One of the most important results is that the dialogue flexibility must exceed a threshold of 15 - measured with two of the metrics- to increase significantly the user's performance