Towards a Practical Measure of Hypertext Usability

Disorientation or the sense of being 'lost' in an information space has long been held as a major drawback of hypertext systems. However, the usability of hypertext systems has been difficult to evaluate as the commonly used human-computer interaction measures based on time and errors seem inappropriate for hypertext systems which, by their nature, encourage exploration and browsing. A set of measures are proposed for assessing the usability of hypertext systems in terms of the efficiency with which users find information in a hypertext system; the degree to which users become 'lost' in the information space; and how confident they are in their ability to find relevant information. In particular, various path measures are defined, from which indicators and 'ratings' of users' lostness, efficiency and confidence when using a hypertext system are derived. An initial experimental evaluation of the measures is described in which observations were made of the 'success' of the searches and of the routes which were taken by the users while carrying out specified tasks. A discussion of the method by which the measures were calibrated using both an attitudinal study and the verbal and video protocols recorded as part of the experiment is presented. Results from an independent experimental study are also briefly discussed. Finally, an analysis is offered of the situations in which these measures may be appropriate.