An introduction to the Bernoulli CUSUM

The Bernoulli CUSUM (BC) provides a moving window of process performance and is the quickest control chart to detect small increases in fraction defective. The Bernoulli CUSUM designs presented here require 2, 3, or 4 failures in a moving window to produce a signal. The run length distribution provides insight into the properties of the BC beyond the Average or Median Run length. A retrospective analysis of electronic component pass/fail data using the BC suggested that a problem may have been present during previous production. Subsequent production used the BC for real time process performance feedback.