Quality Control Procedures, Documentation and Interpretation: Cumulative Summation Limit

CUSUM Example: Exceeding the CUSUM Limit

  • On March 10, the CUSUM is nearing the CUSUM Limit calculated in formula E. This should serve as a warning. While patient results are still "in control," there is a trend indicating that they will soon not be.
  • Sure enough, on March 11, the CUSUM reaches -4, which is the CUSUM Limit, and patient results cannot be accepted as accurate.
  • It is important to observe daily any trends in the CUSUM values so that corrective action can be taken before the limit is reached.

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