How to measure and to quantify usability of user interfaces

One of the main problems of standards in the context of the usability of software quality is that the standards cannot be measured in terms of product features. We present a new approach to measure user interface quality in a quantitative way. First, we develop 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 of the known interface types. We distinguish between different types of `interaction points'. With these kinds of interaction points, we can describe several types of interfaces: conventional user interfaces (CUI), such as command-driven, menu-driven and form fill-in, and graphical user interfaces (GUI), such as desktops, direct manipulation, multimedia, etc. We carried out two different comparative usability studies to validate our quantitative measures. The results of one other published comparative usability study can be predicted. The results of six different interfaces are presented and discussed