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378 HUMAN PERFORMANCE IN MOTION PLANNING

overall human performance. The p-level for the visibility factor shows that the
overall human performance is only slightly improved in the visible environment
compared to the invisible environment.
Given a significant effect indicated by the MANOVA results, multiple uni-
variate ANOVAs have followed.
2. The MANOVA was applied to the right-to-left data in Experiment One.
The variables are as follows:
• Dependent variables:
1. Path length.
2. Completion time.
• Independent variables:
1. Interface, with 2 levels: virtual and physical.
2. Visibility, with 2 levels: visible and invisible.

The results are shown in Table 7.16. Note that the p-level for the interaction
effect between the two independent variables is large enough; we can conclude
that there is no interaction effect. This means that the effect of one independent
variable is not influenced by the other independent variable. The p-level for the
interface factor is almost zero, hence we reject the null hypothesis of MANOVA.
That is, the interface factor has a statistically significant effect on the overall
subjects’ performance. The p-level for the visibility factor is large; we thus
conclude that the overall subjects’ performance was affected by the visibility
factor.
Since a significant effect was demonstrated by this MANOVA, multiple uni-
variate ANOVAs have followed.
3. MANOVA was applied to the Experiment Two data. The variables involved
are as follows:

• Dependent variables:
1. Path length.
2. Completion time.

TABLE 7.16. Results of MANOVA for RtoL Task, Experiment One
MANOVA Effects Studied: 1—interface, 2—visibility
Effect Wilks’ Lambda df 1 df 2 p-Level
1 0.406424 2 90 0.000000
2 0.988945 2 90 0.606390
12 0.990999 2 90 0.665716