Westgard rules are generally applied when the number of control measurements per run is:

Westgard rules are generally applied when the number of control measurements per run is:

• A. One
• B. Two or Four
• C. Three
• D. Five

Answer: (B)

Westgard rules rely on having multiple control measurements within a single run to judge whether the process is in control and to detect different types of error. With only one control measurement, you don’t have enough information to assess variability or to apply the standard multi-rule criteria reliably. Having two control measurements per run gives enough data to evaluate both bias and imprecision and to apply the common rules that signal out-of-control conditions. Some laboratories also run four control measurements per run, which provides even more data and allows applying a broader set of rules within the same run, increasing fault detection without sacrificing throughput. For these reasons, Westgard rules are generally applied when the number of control measurements per run is two or four.

Westgard rules rely on having multiple control measurements within a single run to judge whether the process is in control and to detect different types of error. With only one control measurement, you don’t have enough information to assess variability or to apply the standard multi-rule criteria reliably. Having two control measurements per run gives enough data to evaluate both bias and imprecision and to apply the common rules that signal out-of-control conditions. Some laboratories also run four control measurements per run, which provides even more data and allows applying a broader set of rules within the same run, increasing fault detection without sacrificing throughput. For these reasons, Westgard rules are generally applied when the number of control measurements per run is two or four.