The influence of design decisions on the usability of direct manipulation user interfaces

It is assumed that the usability of direct manipulation user interfaces is influenced by a number of design aspects. In this experimental study, the order of command specification and the type of function activation were manipulated in a 2 × 2 factorial design, in order to test hypotheses H1, that object-function specification contributes more to usability than function-object specification; and H2. that the type of function activation (clicking vs. dragging) will influence the usability of direct manipulation user interfaces. Sixty-four subjects, balanced by sex, without computer experience, were assigned randomly to the four experimental conditions. The dependent variables include performance data such as time, efficiency and error rates (logfile-recording), and subjective user rating of the user interface (questionnaire). Whereas HI had to be rejected in this general form, a more elaborated analysis showed significant differences between the factor levels in terms of performance time and syntactically correct actions. Furthermore, the results of the study demonstrated evidence for H2.