Measuring Usability: 
       Evolving Quality Metrics 
      for User Interface Designs

          Larry Constantine
    Professor of Computing Sciences
    University of Technology, Sydney

Predictive usability metrics are an emerging and promising
approach to assessing and improving the quality of user interface designs
Although metrics have long played an important role in computer science and
software engineering, little has been done in applying metric strategies to
software usability and user interface design. Traditional approaches to
measuring software usability have centered on testing, and the schemes for
laboratory and field testing are well established. However, because testing
depends on having something to test--software, prototype, or simulation-- it
is difficult to conduct testing early in the design process. Ideally,
designers would like to be able to predict usability based on metrics
computed from visual designs or paper prototypes. A pragmatic suite of
metrics has been developed for this purpose, including simple structural
measures as well as content-sensitive and task-sensitive metrics devised to
support decision making by practicing developers. The suite, comprising
five complementary metrics, has been the subject of both heuristic and
preliminary formal validation. Previous work will be discussed and the
current status of the design metric suite will be presented.



Larry L. Constantine, Professor of Computing Sciences, University of
Technology, Sydney, Australia, and Principal Consultant, Constantine &
Lockwood, Ltd., is one of the pioneers of modern software engineering
practice. In a career spanning 35 years he has become recognized for
contributions in both the human sciences and the information sciences. An
international consultant on software usability and the human side of
software development, he commutes regularly to and from Australia and
Europe. A graduate of Massachusetts Institute of Technology, he has served
on the faculties of five major universities. His publications include
_Software for Use: A Practical Guide to the Models and Methods of
Usage-Centered Design_ (Addison-Wesley, 1997), written with Lucy Lockwood,
_Constantine on Peopleware_ (Prentice Hall, 1995) and the classic text,
_Structured Design_ (with ed Yourdon), as well as more than 100 published
papers. His current research interests are focussed on improved methods and
tools for supporting rapid visual development.