Page 152 - Six Sigma Demystified

Chapter 6 a n a ly z e S tag e 133

decrease in distance from the target of 7 units, and the effect of boulder weight
is estimated as a decrease of 8 units in distance from the target.
Based on these observations, distance from the target is minimized by setting
the factors as follows: rubber band: large; drawback distance: short; and boulder
weight: light.
The problem with this traditional one- factor- at- a- time experiment is that it
ignores the possible effects of interactions between the three factors. The inter-
action plot shown in Figure 6.6 is from a designed experiment of the same
process. At the high rubber band setting (shown by the line labeled 330), a
distance from the target of 21.0 is observed at the short condition of drawback.
This is trial 2 from Table 6.1. Trial 3 is shown on the line labeled 210 at the long
condition of drawback distance.
On the 210 rubber band size setting, there is very little change in the dis-
tance from the target moving from a short to a long condition of drawback
distance (left to right along the line). This implies that drawback distance makes
little difference when a small rubber band is used.

Figure­6.6 interaction chart showing interaction between rubber band size
and drawback distance.