Figure 4 shows box plots of Time for each combination of
Workstation and index of difficulty (ID) grouped by ID. Notice that
the Walk Workstation has the highest Time value for all four ID values.
This suggests that walking will result in lower worker productivity
than the sitting or standing across the range of task complexity. The
presence of a significant Workstation-Distance interaction combined
with the absence of a Workstation-Size interaction shows that the
two aspects of task difficulty (Size and Distance) may not combine
in the same fashion for each Workstation. Figure 5 shows the same
box plots as Figure 4 with index of difficulty relabeled as Distance and
Size. Looking at the data this way explains the apparent anomaly when
using index of difficulty. Small targets Close together have an ID of 3
while Large targets Far apart have an ID of 4. At the Walk or Stand
Workstations these two combinations result in similar Time values;
however, when using the Sit Workstation, Small targets Close together
have lower times than Large targets Far apart. This suggests that in the
seated posture, target proximity has more impact on response time
than target size.