1. Statistical Reference Guide
  2. Process capability

Nonconforming unitsNonconforming units describe the number of nonconforming units a process produces, expressed in parts per million.

The number of nonconforming units is an alternative to traditional Cp and Pp indices. They are easily understandable by end-users.

The number of nonconforming units is either:

  • The actual number of nonconforming units in the sample.
  • The expected number of nonconforming units, assuming a normally distributed process quality characteristic with the parameters specified by the process mean and sigma. The process sigma is either the short-term or long-term sigma estimate.

Various indices measure how the process is performing against the specification limits:

Index Description
< LSL The number of nonconforming units that are less than the lower specification limit.
> USL Thr number of nonconforming units that are greater than the upper specification limit.
< SL > The total number of nonconforming units that are outside the specification limits.
Available in
Quality Control & Improvement Edition Ultimate Edition

From the Statistical Reference Guide for Analyse-it 6.24.0: https://analyse-it.com/docs/user-guide/process-capability/non-conforming-units

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