Trueness definition

The trueness definition suggests that a very critical role is bestowed on the accepted reference value. This quantity can be provided by a number of different approaches ... 

For the characterization of the reliability of analytical measurements the terms precision, accuracy, and trueness have a definite meaning. 

Accuracy (Trueness and Precision) of Measurement Methods and Results - Part 1. General Principles and Definitions , ISO 5725-1 1994, International Organization for Standardization (ISO), Geneva, Switzerland 1994. 

When talking about quality of chemical measurements trueness, precision, accuracy and error are some of the more important keywords. Therefore a clear definition is necessary (see also chapter 11, slides 36 and 44). 

ISO 5725—Accuracy (trueness and precision) of measurement methods and results ISO 5725-1 1994 General principles and definitions ISO 5725-2 1994 Basic method for the determination of repeatability and reproducibility of a standard measurement method ISO 5725-3 1994 Intermediate measures of the precision of a standard measurement method ISO 5725-4 1994 Basic methods for the determination of the trueness of a standard measurement method ISO 5725-5 1998 Alternative methods for the determination of the precision of a standard measurement method ISO 5725-6 1994 Use in practice of accuracy values... 

ISO 5725-1 1994 Accuracy (trueness and precision) of measurement methods and results—Part 1 general principles and definitions... 

From a general viewpoint, the credibility and comparability of environmental analytical data can be assessed through two major parameters, i.e., trueness and precision, which combine into accuracy and express the closeness between an experimental measurement with its uncertainty and the true (or supposedly so) value of a given quantity (40). Such concepts were developed long ago, but are still being refined to accommodate the progress made so far in this sector. Definitions of these and other quantities relevant to this field, for which consensus has been achieved by the scientific community, are listed in Table 1.3. 

Results verification is totally different from results validation. Results validation (point 4.7.5. and 5.9. of NBN-EN-ISO-CEI 17025 standard) shows, each year, or when it is judged necessary, that a given laboratory has the capacity to apply a particular method, repetitively, in respect of obtained data during initial validation. Trueness and statistical dispersion of results are the basis of the definition of the uncertainty of the standard of measurement [16] and, in some cases, the basis for the definition of the limit of detection and quantification. Management of data from validation results, as control card, could permit the detection and control of eventual deviation. Validation of results is the internal quality control procedure which verifies the stability of performance of the methods for which accreditation is sought, in the limited-scope procedural context. 

Check if the bias can be neglected through a test of the trueness The definition of trueness (Prichard, 2005) is detailed in Appendix A. The criterion Cobs is compared with 1. It is considered as acceptable if it is less than 1 at a confidence level of 95% (Feinberg, 2001). Where the bias found is judged to be nonsignificant, the uncertainty associated with the bias is simply the combination of the standard uncertainty on the CRM value with the standard deviation associated with the bias (Eurachem, 2000). 

Definitive method method with a high scientific status applied in a laboratory of high proven quality [10]. In brief it means that only negligible systematic errors may remain compared to the precision and trueness required for the final result. Isotope Dilution Mass Spectrometry (IDMS), in its thermo-ionisation mode, for the determination... 

Definition The trueness or accuracy of an analytical method is given by the extent to which the value obtained deviates from the true value. It is often expressed as the amount determined by analysis expressed as a percentage of the known amoimt of active ingredient added to the matrix material. It is a measure of the exactitude of the method. 

Tmeness is a measure of the systematic error (<5M) of the calculated result introduced by the analytical method from its theoretical true/reference value. This is usually expressed as percent recovery or relative bias/error. The term accuracy is used to refer to bias or trueness in the pharmaceutical regulations as covered by ICH (and related national regulatory documents implementing ICH Q2A and Q2B). Outside the pharmaceutical industry, such as in those covered by the ISO [20,21] or NCCLS (food industry, chemical industry, etc.), the term accuracy is used to refer to total error, which is the aggregate of both the systematic error (trueness) and random error (precision). In addition, within the ICH Q2R (formerly, Q2A and Q2B) documents, two contradictory definitions of accuracy are given one refers to the difference between the calculated value (of an individual sample) and its true value... 

Total Error or Measurement Error The measurement error of an analytical procedure expresses the closeness of agreement between the value measured and the value that is accepted either as a conventional true value or an accepted reference value. This is also the definition of accuracy in ICH Q2R. This closeness of agreement represents the sum of the systematic and random errors, that is, the total error associated with the observed result. Consequently, the measurement error is the expression of the sum of the trueness and precision, that is, the total error [19,22]. 

Estimation of trueness and precision The EU directive (Council Directive 98/83/EC, 1998) refers to the definitions for the determination of trueness and precision given in ISO 5725-1 (ISO, 2002). According to this standard, the estimation of the trueness requires a large series of replicate determinations of test samples. But what does Targe series mean Neither ISO 5725-1 nor the EU directive resolve this question. The determination of precision also requires a number of replicate determinations of a test sample. Information on a recommended number of replicates is also missing in ISO 5725-1. 

According to Note 2 of the definition, the term accuracy is sometimes mixed up with measurement trueness and measurement precision. Therefore, we have a look at these two terms that are defined in ISO/IEC Guide 99 (2007), definitions 2.14 and 2.15. 

Accuracy has previously been defined as the same as true ness only, but with ISO 5725-1 (1994), and reflected in the JCGM 200 2012, the definition of accuracy has for the most changed to include both trueness and precision as given here. The old definition is still in use in some areas. 

Definition The closeness of agreement between the average of an infinite number of replicate measured quantity values and a reference quantity value [25]. Description Trueness is not a quantity and cannot be expressed numerically [25]. 

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