On the Benefits of Designing Interactive Systems in terms of Critical Parameters

Critical parameters are quantitative measures of performance that may be used to determine the overall ability of a design to serve its purpose. Although critical parameters figure in almost every field of design where there is a demand for progressive improvement, they do not appear to figure significantly in the design of interactive systems. As a result, systems are designed that are recognizably different from other systems but not necessarily better at doing the job intended. This paper discusses the role of critical parameters in design, and illustrates their lack of use in interactive system design by presenting a number of of examples drawn from the HCI literature. It identifies a consequent need for research to establish critical parameters for applications and to build models of the performance of designs against these parameters. Some ideas are presented on how critical parameters might be established for specific applications, and the paper concludes by summarising some of the benefits that might be gained from moving in this direction.