This part of ISO 5725 provides basic methods for estimating the bias of a measurement method and the laboratory bias when a measurement method is applied.
It is concerned exclusively with measurement methods which yield measurements on a continuous scale and give a single value as the test result, although the single value may be the outcome of a calculation from a set of observations.
In order that the measurements are made in the same way, it is important that the measurement method has been standardized. All measurements are to be carried out according to that standard method.
Bias values give quantitative estimates of the ability of a measurement method to give the correct (true) result. When a value for the bias of a measurement method is quoted, together with a test result obtained by that method, there is an implication that the same characteristic is being measured in exactly the same way.
This part of ISO 5725 can be applied only if the accepted reference value can be established as a conventional true value, for example by measurement standards or suitable reference materials or by referring to a reference measurement method or by preparation of a known sample.
Reference materials could be either
a) certified reference materials;
b) materials manufactured for the purpose of the experiment with known properties; or
c) materials whose properties have been established by measurements using an alternative measurement method whose bias is known to be negligible.
This part of ISO 5725 considers only those cases where it is sufficient to estimate bias on one level at a time. It is not applicable if the bias in the measurement of one property is affected by the level of a second property (i.e. it does not consider interferences). Comparison of the trueness of two measurement methods is considered in ISO 5725-6.
NOTE 1 In this part of ISO 5725, bias is considered only at one level at a time. Therefore the Index j for the level has been omitted throughout.
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