ISO 5725-1:1994 pdf download – Accuracy (trueness and precision) of measurement methods and results — Part 1: General principles and definitions
ISO 5725-1:1994 pdf download – Accuracy (trueness and precision) of measurement methods and results — Part 1: General principles and definitions.
3.10 bIas of the measurement m,thod The difference between the expectation of test results obLaiiieii horn all labOratories using that method and an accepted reference value.
NOTE 6 On. exampe of this fails to extract al the sulfur. giving a negative bias to the measurement method. The bias of the measurement method is measured by the displacement of me average of results horn a latge number of diffa,ent labuietisiss all using the same method. The bias of a measurement mothod may be different at different level,
3.11 laboratory component of bias: The difference between the laboratory bias and the bias of the measurement method.
8 The laboiatoiy cunjooent of baa relatwe to the overall average result, not the true or rot oronoe value.
3.12 The closeness of agreement between independent test results obtained under stipulated conditions.
9 Precision depends only on the disirbution of random errors and does not relate to the true value or the specifi.d value
10 The measure of precision is usually expressed in terms of inrecisirwi anti rnrripiiterl as a stanrirr1 deviation of the test res&its. Less precision is reflected by a larger standard deviation.
11 independent test results. means results Obtaeied m a manner nut iniloericed by any previous issult un the seine or sirnr test ob1ect. Quantitative measures of precision depend cntically on the stipulated conditions, Repeatability and reproducibarty concahons are particular sets of extreme
3.14 conditions: Conditions where independent test results are obtained with the Same method on identical test items in the same laboratory [ISO 3534-1]
3.15 repeatability standard deviation: The standard deviation of test results obtained under repeatability conditions.
12 It is a measure of dispersion of the distribution of test results under repeatability conditions.
13 Similarly “repeatability variance” and “repeatability coetticient ot variation” could he defined and used as measures of the dispersion of test results under repeatability conditions.
3.16 repeatability limit: The value less than or equal to which the absolute difference between two test results obtained under repeatability conditions may be expected to be with a probability of 95 %.
NOTE 14 The symbol used is r.
3.17 reproducibility: Precision under reproducibility conditions.
3.18 reproducibility conditions; Conditions where test results are obtained with the same method on identical test items in different laboratories with different operators using different equipment.
3.19 reproducibility standard deviation: The standard deviation of test results obtained under reproducibility conditions.
15 It is a measure of the dispersion of the distribution of test results under reproducibility conditions.
16 Similarly “reproducibility variance” and “reproducibility coefficient of variation” could be defined and used as measures of the dispersion of test results under reproducibility conditions.
3.20 reproducibility limit: The value less than or equal to which the absolute difference between two test results obtained under reproducibility conditions may be expected to be with a probability of 95 %.
NOTE 17 The symbol used is R.
3.21 outlier: A member of a set of values which is inconsistent with the other members of that set.
NOTE 18 ISO 5725-2 specifies the statistical tests and the significance level to be used to identify outliers in trueness and precision expcrimonts.
3.22 collaborative assessment experiment: An interlaboratory experiment in which the performance of each laboratory is assessed using the same standard measurement method on identical material.
19 The definitions given in 3.16 and 3.20 apply to results that vary on a continuous scale. If the test resuft is discrete or rounded oft, the repeatability limit and the reproducibility limit as defined above are each the minimum value equal to or below which the absolute difference between two single test results is expected to lie with a probability of not less than 95 %.
20 The definitions given in 3.8 to 3.11, 3.15, 3.16, 3.19 and
3.20 refer to theoretical values which in reality remain unknown. The values for reproducibility and repeatability standard deviations and bias actually determined by experiment (as described in ISO 5725-2 and ISO 5725-4) are, in statistical terms, estimates of these values, and as such are subject to errors. Consequently, for example, the probability levels associated with the limits r and R will not be exactly 95 %. They will approximate to 95 % when many laboratories have taken part in the precision experiment, but may be considerably different from 95 % when fewer than 30 laboratories have participated. This is unavoidable but does not seriously detract from their practical utility as they are primarily designed to serve as tools for judging whether the difference between results could be ascribed to random uncertainties inherent in the measurement method or not. Differences larger than the repeatability limit r or the reproducibility limit R are suspect.