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ISO 5725-3

1st Edition, December 15, 1994

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Accuracy (Trueness and Precision) of Measurement Methods and Results - Part 3: Intermediate Measures of the Precision of a Standard Measurement Method

Includes all amendments and changes through Technical Corrigendum 1, October 15, 2001

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This part of ISO 5725 specifies four intermediate precision measures due to changes in observation conditions (time, calibration, operator and equipment) within a laboratory. These intermediate measures can be established by an experiment within a specific laboratory or by an interlaboratory experiment.

Furthermore, this part of ISO 5725

a) discusses the implications of the definitions of intermediate precision measures;

b) presents guidance on the interpretation and application of the estimates of intermediate precision measures in practical situations;

c) does not provide any measure of the errors in estimating intermediate precision measures;

d) does not concern itself with determining the trueness of the measurement method itself, but does discuss the connections between trueness and measurement conditions.

This part of ISO 5725 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.

The essence of the determination of these intermediate precision measures is that they measure the ability of the measurement method to repeat test results under the defined conditions.

The statistical methods developed in this part of ISO 5725 rely on the premise that one can pool information from "similar" measurement conditions to obtain more accurate information on the intermediate precision measures. This premise is a powerful one as long as what is claimed as "similar" is indeed "similar". But it is very difficult for this premise to hold when intermediate precision measures are estimated from an interlaboratory study. For example, controlling the effect of "time" or of "operator" across laboratories in such a way that they are "similar", so that pooling information from different laboratories makes sense, is very difficult. Thus, using results from interlaboratory studies on intermediate precision measures requires caution. Within-laboratory studies also rely on this premise, but in such studies it is more likely to be realistic, because the control and knowledge of the actual effect of a factor is then more within reach of the analyst.

There exist other techniques besides the ones described in this part of ISO 5725 to estimate and to verify intermediate precision measures within a laboratory, for example, control charts (see ISO 5725-6). This part of ISO 5725 does not claim to describe the only approach to the estimation of intermediate precision measures within a specific laboratory.

NOTE 1 This part of ISO 5725 refers to designs of experiments such as nested designs. Some basic information is given in annexes B and C. Other references in this area are given in annex E.
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