Which Westgard rule requires 10 consecutive control measurements to fall on one side of the mean?

Which Westgard rule requires 10 consecutive control measurements to fall on one side of the mean?

• A. 1(3s) Westgard Rules
• B. 1(2s) Westgard Rules
• C. 10x Westgard Rules
• D. R(4s) Westgard Rules

Answer: (C)

The idea here is to recognize how Westgard rules detect bias in control results. The rule that requires ten consecutive control measurements to fall on the same side of the mean is designed to flag a persistent shift in the process—a bias that keeps pushing results consistently higher or lower than the target. This isn’t about a single outlier, but about a sustained deviation that suggests the instrument, reagent, or calibration has moved. Think of it as watching a control chart: if you see ten in a row all above the target or all below it, that pattern strongly indicates a systematic change rather than random fluctuation. Other rules focus on isolated events or short runs that exceed a certain number of standard deviations, or on the range between consecutive points, which detect random errors or sporadic issues rather than a steady bias. That combination makes the ten-consecutive-on-one-side rule the one that specifically demands ten in-a-row on one side of the mean.

The idea here is to recognize how Westgard rules detect bias in control results. The rule that requires ten consecutive control measurements to fall on the same side of the mean is designed to flag a persistent shift in the process—a bias that keeps pushing results consistently higher or lower than the target. This isn’t about a single outlier, but about a sustained deviation that suggests the instrument, reagent, or calibration has moved.

Think of it as watching a control chart: if you see ten in a row all above the target or all below it, that pattern strongly indicates a systematic change rather than random fluctuation. Other rules focus on isolated events or short runs that exceed a certain number of standard deviations, or on the range between consecutive points, which detect random errors or sporadic issues rather than a steady bias. That combination makes the ten-consecutive-on-one-side rule the one that specifically demands ten in-a-row on one side of the mean.