Page 196 - Lean six sigma demystified

Chapter 5 Redu C ing d efe C t S with Six Sigm a 175

FIGURE 5-29 • Cause-and-effect matrix.

Another tool that’s sometimes used to identify causes and effects is the
cause-effect matrix (Fig. 5-29).
The fishbone is not only useful for identifying the root cause of recurring
problems (common cause variation), but it can also be extremely useful when
stabilizing a process. Special causes of variation (e.g., power spikes, cable cuts,
and so on) result in unstable processes as well.
Suppose there is a computer outage. The problem statement becomes: On
January 31, System X went down putting 600 service reps out touch with
service systems.
Major contributors to this problem can be identified and root causes deter-
mined. When collected over time, these special cause analyses will give you the
data to cost-justify the improvements necessary to prevent them.