Each horizontal line represents one standard deviation. (A) A Levy–Jennings plot of the mentor results around the optimum of 100%. The results of an adept laboratory are compared with a mentor laboratory when measuring the concentration of hemoglobin in whole blood.
A mentor (split sample) technique for quality control. Decision tree when considering whether to eliminate bias. This is because some bias components become random over time. As the length of time observed increases, the random error increases and bias decreases. Step 4: The repeatability – the random error occurring between replicate determinations performed within a short period of time. Step 3: The day-to-day variation – a combination of random error and short-term bias owing to, among other factors, time effects, change of reagents and so on. Step 2: The method and/or measurement system bias. The ‘laboratory’ can be a single laboratory or a laboratory organization, for example, all laboratories within a community that a patient is using. Step 1: The laboratory bias – a bias for an individual laboratory. (B) Ladder represents a situation common in clinical chemistry where a laboratory measures samples in a number of different locations, using several methods and measurement systems.
(A) Ladder represents a laboratory using essentially a single measurement method and measurement system for serving their customers. The ladder of errors for measures one parameter in clinical chemistry according to the concept introduced by Thompson et al.
The random error component of the uncertainty in determining the mean is inversely related to the square root of the number of observations – the standard error of the mean. The components of error (random and systematic error) of (A) a single result of measurement, (B) the mean of four replicate measurements and (C) the mean of infinite number of measurements, which eliminates the random error component. The dotted line from bias to measurement uncertainty is to indicate that if bias can be estimated, it should be eliminated.Īdapted with permission from © Springer (2007). Įxplaining the relationships between concepts describing random and systematic errors, as well as measurement uncertainty. Currently, repeatability and day-to-day variation contribute less than bias to the expanded uncertainty of high-volume measurement methods in clinical chemistry.
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