Quality Control Procedures, Documentation and Interpretation: Westgard Rules

Shifts

  • A shift, on the other hand, describes a sudden change in the data mean that persists throughout further days of testing.
  • Shifts can be caused for any number of reasons, including persistent instrument malfunction, loss of calibration, or improper reagents.
  • Shifts are often easier to recognize than trends, as the data may be more clearly suspect.
  • Again, shifts must be corrected as soon as possible, as patient data are most likely already invalid.
  • In the example to the right, the large jump on day 5 followed by persistently high control values means that a shift has occurred.

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