Which Westgard rule is violated when ten consecutive control measurements fall on one side of the mean?

Which Westgard rule is violated when ten consecutive control measurements fall on one side of the mean?

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

Answer: (C)

A persistent bias in the analytical process is indicated when ten consecutive control measurements fall on the same side of the mean. This pattern shows the results aren’t just random scatter around the target; the process has shifted and stayed biased in one direction for a substantial sequence. In Westgard QC, this specific pattern triggers the 10x rule, signaling an out-of-control condition and the need to investigate potential causes such as calibration drift, a reagent issue, instrument misalignment, or a procedural change. This is why the 10x rule fits best here: it detects a nonrandom, sustained shift rather than a single outlier or a pair of results beyond a limit, which would point to different issues. For context, a lone point beyond ±3 SD would be just an isolated anomaly; two consecutive points beyond ±2 SD suggest a possible issue but not a long-running bias; the R(4s) rule flags problems with precision within a run, not a persistent bias across many results.

A persistent bias in the analytical process is indicated when ten consecutive control measurements fall on the same side of the mean. This pattern shows the results aren’t just random scatter around the target; the process has shifted and stayed biased in one direction for a substantial sequence. In Westgard QC, this specific pattern triggers the 10x rule, signaling an out-of-control condition and the need to investigate potential causes such as calibration drift, a reagent issue, instrument misalignment, or a procedural change.

This is why the 10x rule fits best here: it detects a nonrandom, sustained shift rather than a single outlier or a pair of results beyond a limit, which would point to different issues. For context, a lone point beyond ±3 SD would be just an isolated anomaly; two consecutive points beyond ±2 SD suggest a possible issue but not a long-running bias; the R(4s) rule flags problems with precision within a run, not a persistent bias across many results.