92 Virtual-reality–based rehabilitation systems. In Robotica

(Vol. 22, 2004), researchers described a study of the effectiveness of display devices for three virtual-reality

(VR)-based hand rehabilitation systems. Display device A is a projector, device B is a desktop computer monitor, and device C is a head-mounted display. Twelve nondisabled right-handed male subjects were randomly assigned to the three VR display devices, four subjects in each group. In addition, within each group two subjects were randomly assigned to use an auxiliary lateral image and two subjects were not. Consequently, a 3 * 2 factorial design was employed, with the VR display device at three levels (A, B, or C) and an auxiliary lateral image at two levels (yes or no). Using the assigned VR system, each subject carried out a “pick- and-place” procedure and the collision frequency

(number of collisions between moved objects) was measured.

a. Give the sources of variation and associated degrees of freedom in an ANOVA summary table for this design.

b. How many treatments are investigated in this experiment?

c. The factorial ANOVA resulted in the following p -values:

Display main effect (.045), Auxiliary lateral image main effect (.003), and Interaction (.411). Interpret these results practically. Use a = .05 for each test you conduct.