3. Results
The across-subject mean of each COP parameter, separately for
each task and time of day, is illustrated in Fig. 1. The graphs show
that all parameters consistently differed between tasks, but differences
between times of day are less obvious.
The Pearson correlations between COP parameters are listed in
Table 1, which shows that for each task and time of day, there was a
strong correlation between COP path length and COP velocity; a
strong correlation between COP confidence area, anterioreposterior
sway, and mediolateral sway; but a poor correlation between
the former two and the latter three parameters. Accordingly, factor
analyses of each task and time of day reduced the five parameters
to the same two factors, one representing path length and speed,
and the other representing variability and confidence area (see
Table 2). Although each factor analysis relies on only a small
number of participants, all 10 analyses yielded comparable outcomes
and were in line with the 10 correlation matrices of Table 1,
which supports their validity. From this we concluded that the
same factorial structure applies to all tasks and times of day, thus
allowing comparisons based on factor values rather than parameter
scores. Fig. 2 illustrates that the values of F1, but not those of F2,
differed consistently between times of day in all tasks. ANOVA of F1
yielded significance for time of day [F(1,34) ¼ 10.70; p < 0.01] and
task [GreenhouseeGeisser-corrected F(3,102) ¼ 86.23; p < 0.001],
but not for the interaction. ANOVA of F2 revealed significance only
for task [F(3,102) ¼ 35.77; p < 0.001].
3. ResultsThe across-subject mean of each COP parameter, separately foreach task and time of day, is illustrated in Fig. 1. The graphs showthat all parameters consistently differed between tasks, but differencesbetween times of day are less obvious.The Pearson correlations between COP parameters are listed inTable 1, which shows that for each task and time of day, there was astrong correlation between COP path length and COP velocity; astrong correlation between COP confidence area, anterioreposteriorsway, and mediolateral sway; but a poor correlation betweenthe former two and the latter three parameters. Accordingly, factoranalyses of each task and time of day reduced the five parameters to the same two factors, one representing path length and speed,and the other representing variability and confidence area (seeTable 2). Although each factor analysis relies on only a smallnumber of participants, all 10 analyses yielded comparable outcomesand were in line with the 10 correlation matrices of Table 1,which supports their validity. From this we concluded that thesame factorial structure applies to all tasks and times of day, thusallowing comparisons based on factor values rather than parameterscores. Fig. 2 illustrates that the values of F1, but not those of F2,differed consistently between times of day in all tasks. ANOVA of F1yielded significance for time of day [F(1,34) ¼ 10.70; p < 0.01] andtask [GreenhouseeGeisser-corrected F(3,102) ¼ 86.23; p < 0.001],
but not for the interaction. ANOVA of F2 revealed significance only
for task [F(3,102) ¼ 35.77; p < 0.001].
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