Lost in hyperspace: metrics and mental models

Being disorientated or lost is one of the fundamental dif®culties which users experience when trying to navigate within hypertext systems. In this paper, two new metrics of lostness are described and applied. The new metrics focus on the effects of link-type and the accuracy of user's mental models of system structure. In a series of studies, the new metrics were compared with the only other published metric of lostness, the optimal path deviation measure formulated by Smith [P.A. Smith, Towards a practical measure of hypertext usability, Interacting with Computers 4 (1996) 365±381], and with other measures including self-report estimates and task times. The results tentatively suggest that some types of hyperlink have a greater impact on lostness than others. The accuracy of the subjects' mental models did not correlate signi®cantly with other measures of lostness, however this may have been due to task demands. Based on these ®ndings, suggestions are made for the design of more effective hypertext systems that minimise lostness, and a new approach to designing such systems, based on the mental models of users, is put forward. q 2000 Elsevier Science B.V. All rights reserved.