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  • A trend shows a slow movement of the data mean from one level to another.
  • A trend is indicative of a systematic error that is occurring slowly, such as reagent deterioration, control deterioration, or a lens getting progressively dirtier.
  • In the example to the right, some type of systematic error began on day 6, and by day 10, we can say that a trend has occurred and results are out of control.
  • Be on the lookout for trends as they begin to take shape, and you may be able to avoid further quality control problems.