The Measure Stage - Six Sigma


The Measure Phase has a number of key purposes:

  • Establish Metrics and Measurement System: What are the Critical to Quality (CTQ) elements? How should they be measured? Is the measurement system capable of discriminating to an appropriate level?

  • Listen to the Voice of the Process: Understand present levels of performance in detail. Is the process stable? If so, what is the level of capability?


The Measure Phase has a series of interlinked actions, the numbers imply a sensible order, but this may well be an iterative process:

  • Select Metric and Measurement System: Remember to review the question being asked and to generate the most appropriate measure. This may not always be as obvious as it first appear (see info box).

  • Run Control Charts: Control charts are the only effective way of establishing whether a process is stable or whether it is under the influence of special causes.

  • Assess Process Capability (Sigma Level): Using DPMO measures we can establish a notional sigma level for the process, or using conventional process capability approaches we can calculate a Cp or Cpk value. Of course, the assumption of normality means that we need to establish stability before either of these metrics can usefully be calculated.

Principal Tools and Techniques

This is pretty self - explanatory, to establish process stability it will be necessary to apply some form of control chart, the actual combination selected will depend upon the situation. Measurement System Analysis or Gauge Repeatability and Reproducibility Studies would normally be associated with ensuring an acceptable measurement system is used and Process Capability Analysis or DPMO / Sigma level calculations will effectively assess the current process capability with respect to customer requirements.

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