Comparing the power of quality-control rules to detect persistent systematic error.

A simulation approach that allows direct estimation of the power of a quality-control rule to detect error that persists until detection is used to compare and evaluate the error detection capabilities of a group of quality-control rules. Two persistent error situations are considered: a constant shift and a linear trend in the quality-control mean. A recently proposed "moving slope" quality-control test for the detection of linear trends is shown to have poor error detection characteristics. A multimean quality-control rule is introduced to illustrate the strategy underlying multirule procedures, which is to increase power without sacrificing response rate. This strategy is shown to provide superior error detection capability when compared with other rules evaluated under both error situations.