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RESULTS—EXPERIMENT TWO 377

six were randomly picked among the virt–invis–RtoL data. The second half (12
subjects) of the data in the new combined set are the day 2 data (12 subjects)
from Experiment Two.
The purpose of MANOVA or ANOVA analysis on this combined data set is
to test whether human performance would show improvement from day 0, when
the subjects executed tasks without any training (in Experiment One), to day
2, when subjects had a benefit of several training trials (in Experiment Two).
The effect of visibility would also be tested here. Note, however, that the day
factor in this analysis is not a repeated measure variable any longer but instead
a between-subjects variable. This is because there are no pairs of data for day
0 and day 2 coming from the same subjects (which would be required by the
definition of repeated measure variable). The data for day 0 are independent with
respect to the data for day 2. Therefore, the new combined data form a two-way
array, 2 (day) × 2 (visibility).

7.5.3 Results and Interpretation
1. The MANOVA scheme was applied to the left-to-right data in Experiment
One. The variables involved 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 7.15. Here df is the degrees of freedom (see
Section 7.4.5). Note that the p-level for interaction between the two independent
variables is significantly high. We thus conclude that there is no interaction effect.
This means that the effect of one independent variable does not change across
the levels of the other independent variable. The p-level for the interface factor
is almost zero. We therefore reject the null hypothesis of the MANOVA, and
we conclude that the interface factor has a statistically significant effect on the

TABLE 7.15. Results of MANOVA for LtoR Task, Experiment One
MANOVA Effects Studied: 1—interface, 2—visibility
Effect Wilks’ Lambda df 1 df 2 p-Level
1 0.615711 2 90 0.000000
2 0.924517 2 90 0.029253
12 0.986327 2 90 0.538205