One approach to reducing the costs of usability testing is to facilitate the automatic detection of critical incidents: serious breakdowns in interaction that stand out during software use. This research evaluates the use of undo and erase events as indicators of critical incidents in Google SketchUp (a 3D-modeling application), measuring an indicator's usefulness by the numbers and types of usability problems discovered. We compared problems identified using undo and erase events to problems identified using the user-reported critical incident technique [Hartson and Castillo 1998 ]. In a within-subjects experiment with 35 participants, undo and erase episodes together revealed over 90% of the problems rated as severe, several of which would not have been discovered by self-report alone. Moreover, problems found by all three methods were rated as significantly more severe than those identified by only a subset of methods. These results suggest that undo and erase events will serve as useful complements to userreported critical incidents for low cost usability evaluation of creation-oriented applications like SketchUp.
Akers et al. instrumented Google SketchUp [3] , a 3-D modeling application, and recorded invocations of undo and erase events REF .
Undo and erase events as indicators of usability problems
CHI
Computer Science