A formal framework for interpreting the links between usability and utility

When an interface, an information system, a piece of software, and more generally a goal-directed object is evaluated, its implementation (its utilisation) and its results (the goals that can be attained with it and their conformity to the intended goals) have to be evaluated. Implementation and results are described by variables: the variables of usability and utility respectively. Different models of relations between usability and utility can be found in human computer interaction literature, but they don’t allow the reader to interpret the relations between empirical results in usability and utility tests. In this paper a formal framework for the interpretation of fifteen types of relations between these two variables is proposed. This framework permits an evaluation of the impact of usability improvement and utility improvement on the interface’s global quality.