Page 150 - The Six Sigma Project Planner

Example
Assume the same process as in the previous example, i.e., the error rate for a billing
process. However, we do not know the production sequence of the bills. All we know is
that during the previous 26 weeks 10 million bills were sent and 75,000 errors were
identified by customers. What is the process actual DPMO and sigma level?

Solution
The aggregate data can be used to estimate the actual DPMO level, but not the process
capability. The reported error rate is equivalent to a DPMO level of 7,500. Adjusting for
the 1.5σ shift gives a process sigma level of 3.9.
Note: The sigma level of 3.9 represents actual process performance, not capability.
Without the information contained in the time sequence, it is not possible to determine
capability. Remember: when the goal is to understand a dynamic business process,
knowledge of the production sequence of the data is vital.

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