Process Capability

Process capability is used to measure conformance to customer requirements. It can determine whether a process, given its natural variation, is capable of meeting established customer requirements or specifications. Process capability:

  • Helps a team answer the question “Is the process capable?”
  • Helps to determine if there has been a change in the process
  • Helps to determine percentage of product or service not meeting customer requirements

During a quality improvement initiative, such as Six Sigma [Attn: Non-MDH link], a capability estimate is typically obtained at the start and end of the study to reflect the level of improvement that occurred.

Several capability estimates are in widespread use, including:

Cp

Cpk

 These are process capability estimates. They show how capable a process is of meeting its specification limits, used with continuous data.

σ

 Sigma is a capability estimate typically used with attribute data (e.g., with defect rates).


Capability estimates like these essentially reflect the nonconformance rate of a process by expressing this performance in the form of a single number. Typically this involves calculating some ratio of the specification limits to process spread.

Further Reading

Source

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