In daily quality control practice, which statement best describes the Westgard 1-3s rule?

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Multiple Choice

In daily quality control practice, which statement best describes the Westgard 1-3s rule?

The main idea here is that Westgard 1-3s uses a single control result compared to the established mean and its standard deviation. If one control measurement falls more than three standard deviations from the mean, the rule is triggered. Because, under a normal distribution, values beyond ±3 SD are very unlikely to occur by chance, such a point suggests an unusual issue in that run—think random error, instrument fluctuation, or a reagent or sample problem. This is treated as a warning to investigate and perhaps repeat the control and patient measurements, rather than declaring the entire run out of control. Other rules address trends or multiple consecutive deviations, which is why this single outlier beyond 3 SD best describes the 1-3s rule.

The main idea here is that Westgard 1-3s uses a single control result compared to the established mean and its standard deviation. If one control measurement falls more than three standard deviations from the mean, the rule is triggered. Because, under a normal distribution, values beyond ±3 SD are very unlikely to occur by chance, such a point suggests an unusual issue in that run—think random error, instrument fluctuation, or a reagent or sample problem. This is treated as a warning to investigate and perhaps repeat the control and patient measurements, rather than declaring the entire run out of control. Other rules address trends or multiple consecutive deviations, which is why this single outlier beyond 3 SD best describes the 1-3s rule.

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