Trueness accuracy

As stated further above, under all circumstances trueness, accuracy and sensitivity of the assay should be demonstrated on a sufficient number of patient samples. In our view, however, the use of an additional, also easily realizable chromatographic dimension (online-SPE-LC-MS/MS) [67, 68] without a doubt represents the analytical state of the art in immunosuppressant TDM. Nowadays tandem MS instruments are used almost exclusively for the detection and quantification of analytes. The detection of analytes is generally performed in the selected reaction monitoring (SRM, synonym MRM) mode. Depending on which instrumentation is used, an analysis can be completed within two to four minutes. 

Define the analytical performance characteristics precision, trueness, accuracy, selectivity, dynamic range, working range, recovery, robustness, detection limit, and limit of determination. 

Figure 4.1 Diagrams depicting relationships of trueness, accuracy, and precision, (a) Connection map among the error, performance characteristics during measurements, and the quantitative performance characteristics. The measurement is more accurate when it presents a smaller measurement error, more true when the bias is small, and more precise when the random error is small [22]. Adapted from Ref I23J, with kind permission from Springer Science+Business Media, (b) Bull s-eye target representations of shooting patterns manifesting good and poor trueness, accuracy, and precision...

The corabination of an inductively coupled plasma ion source and a magnetic sector-based mass spectrometer equipped with a multi-collector (MC) array [multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS)] offers precise and reliable isotope ratio data for many solid elements. In fact, MC-ICP-MS provides data, the trueness (accuracy) and precision of which is similar to, or, in some cases, even superior to, that achieved by thermal ionization mass spectrometry (TIMS), considered the benchmark technique for isotope ratio measurements of most solid elements [1], The basic strength of ICP-MS lies in the ion source, which achieves extremely high ionization efficiency for almost all elements [2, 3]. Consequently, MC-ICP-MS is likely to become the method of choice for many geochemists, because it is a versatile, user-friendly, and efficient method for the isotopic analysis of trace elements [4-8], The ICP ion source also accepts dry sample aerosols generated by laser ablation [9-16], The combination of laser ablation (LA) with ICP-MS is now widely accepted as a sensitive analytical tool for the elemental and isotopic analysis of solid samples. 

The accuracy of an analytical procedure expresses the closeness of agreement between the value, which is accepted either as a conventional true value or an accepted reference value and the value found. This Is sometimes termed trueness . 

The reliability of multispecies analysis has to be validated according to the usual criteria selectivity, accuracy (trueness) and precision, confidence and prediction intervals and, calculated from these, multivariate critical values and limits of detection. In multivariate calibration collinearities of variables caused by correlated concentrations in calibration samples should be avoided. Therefore, the composition of the calibration mixtures should not be varied randomly but by principles of experimental design (Deming and Morgan [1993] Morgan [1991]). 

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

The ISO recommendation [1993] should be followed and accuracy used only as a qualitative term. In case of quantitative characterization (by means of the bias), a problem may appear which is similar to that of precision, namely that a quality criterion is quantified by a measure that has a reverse attribute regarding the property which have to be characterized. If the basic idea of measures can be accepted, which is that a high quality becomes a high value and vice versa, bias is an unsuited measure of accuracy (and trueness). In this sense, accuracy could be defined by means of a measure proposed in the next paragraph. 

Precision, accuracy and trueness are important performance characteristics in analytical chemistry. Each of them is well-defined in a positive sense ( closeness of agreement... ). However, their quantifying is done by means of unfavourable measures, namely by error quantities like, e.g., standard deviation and bias, respectively, which indeed do quantify imprecision and... 

Accuracy and trueness have been defined above and it was mentioned that these terms base on qualitative concepts (ISO 3534-1 [1993]). If it is necessary to have quantitative information, the bias, which is a measure of inaccuracy, should not be used to quantify accuracy and trueness, respectively. Instead of this, the following measures might be applied... 

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. 

Some authors use the word trueness instead of accuracy to describe the closeness of the mean of many replicate analyses to the true value. This allows the word accuracy to carry a more general meaning which relates to the accuracy or difference of a single result from the true value, as a conse-... 

International Organization for Standardization (ISO), Statistical methods for quality control, Vol. 2, 4th Edition, Accuracy (trueness and precision) of measurement methods and results - Part 2 Basic method for the determination of repeatability and reproducibility of a standard measurement method, ISO 1994(E), 5725-2. 

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). 

Accuracy expresses the closeness of a result to the true value. Accuracy = trueness + precision. Under specific conditions it is quantified by the measurement uncertainty. Measurement uncertainty may vary under changing conditions and method validation determines the degree. 

Method validation seeks to quantify the likely accuracy of results by assessing both systematic and random effects on results. The properly related to systematic errors is the trueness, i.e. the closeness of agreement between the average value obtained from a large set of test results and an accepted reference value. The properly related to random errors is precision, i.e. the closeness of agreement between independent test results obtained under stipulated conditions. Accnracy is therefore, normally studied as tmeness and precision. 

A result could have good precision but a bad trueness . That is, all measurements could be repeatable, but the mean value could be far away from the trae value. This is not a good accmacy . Similarly, a result could have good trueness whilst precision could be bad. In this case the mean value may be close to the true value even though precision is low. This is again not a good accuracy . See also chapter 8 for further information. 

International organization for Standardization, Accuracy (trueness and precision) of measurement methods and results, ISO/DIS 5725-1 to 5725-3, Draft versions 1990/91. 

On the one hand, even if an in-house vahdated method shows good performance and reliable accuracy, such a method cannot be adopted as a standard method. In-house validated methods need to be compared between at least eight laboratories in a collaborative trial. On the other hand, a collaborative study should not be conducted with an unoptimized method [58]. Interlaboratory studies are restricted to precision and trueness while other important performance characteristics such as specificity and LOD are not addressed [105]. For these reasons, single-laboratory validation and interlaboratory validation studies do not exclude each other but must be seen as two necessary and complementary stages in a process, presented in Figure... 

Includes all information on analytical quality control, such a precision clauses (repeatability and reproducibility data), table of statistical data outlining accuracy (trueness and precision) of method... 

Two aspects are important for IQC (1) the analysis of control materials such as reference materials or spiked samples to monitor trueness and (2) replication of analysis to monitor precision. Of high value in IQC are also blank samples and blind samples. Both IQC aspects form a part of statistical control, a tool for monitoring the accuracy of an analytical system. In a control chart, such as a Shewhart control chart, measured values of repeated analyses of a reference material are plotted against the run number. Based on the data in a control chart, a method is defined either as an analytical system under control or as an analytical system out of control. This interpretation is possible by drawing horizontal lines on the chart x(mean value), x + s (SD) and x - s, x + 2s (upper warning limit) and x-2s (lower warning limit), and x + 3s (upper action or control limit) and x- 3s (lower action or control limit). An analytical system is under control if no more than 5% of the measured values exceed the warning limits [2,6, 85]. 

Modern measurement has tried to get away from the traditional concepts of accuracy or trueness. These concepts are based on the false assumption that there is a single true value that lurks in the measurement system and that in principle can be accessed by a sufficient number of measurements done with sufficient attention to detail. In reality, the measurement defines to a large... 

If a method must be developed from scratch, or if an established method is changed radically from its original published form, then before the method is validated, the main task is simply to get the method to work. This means that the analyst is sure that the method can be used to yield results with acceptable trueness and measurement uncertainty (accuracy). When the analyst is satisfied that the method does work, then the essentials of method validation will also have been done, and now just need to be documented. If there is an aspect of the method that does not meet requirements, then further development will needed. Discovering and documenting that the method now does satisfy all requirements is the culmination of method validation. 

Accuracy the degree of closeness of the determined value to the nominal or known true value under prescribed conditions. This is sometimes termed trueness. 

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