Improving uncertainty of linear calibration experiments
Improving uncertainty of linear calibration experiments
Accuracy and Trueness – what is the difference?
In analytical chemistry, we are quite familiar with the statistical term “accuracy” but of late, one may have noticed that the term “trueness” has been referred frequently, particularly in the evaluation of measurement uncertainty by the holistic top down approach which looks at the overall performance of the test method.
Is there a real difference between the meanings of these two terms?
ISO 5725-1 “Accuracy (trueness and precision) of measurement methods and results — Part 1: General principles and definitions” states the following definitions:
Clause 3.6
accuracy The closeness of agreement between a test result and the accepted reference value.
[SOURCE: ISO 3534-1]
Clause 3.7 trueness
The closeness of agreement between the average value obtained from a large series of test results and an accepted reference value.
[SOURCE: ISO 3534-1]
From these definitions, we see that “accuracy” is actually a qualitative term and as suggested by the title of ISO 5725-1, accuracy covers trueness and precision. On the other hand, “trueness“ is statistically quantifiable if we know the closeness of the mean values of repeated testing of a test material from its assigned or certified value. A high level of trueness is equivalent to a lack of bias in the test method.
We can assess “trueness” by one of the following manners:
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