Measurement uncertainty target

Measurement uncertainty is a critical parameter for nearly every kind of analytical system. Parameters in the second column of table 8.3 are not unimportant and must be established, but they are not likely to become limiting factors in the development of the method. In table 8.3, where selectivity is in parentheses, this is not to say that the method should not be demonstrably capable of analyzing the target analyte, but that it should be clear very quickly whether or not the method is doing its job. 

Require to analyze to target measurement uncertainty MU Calibration, ruggedness, (LOD)... 

We have every reason to consider the estimation of measurement uncertainty in an analytical procedure followed by the judgement of compliance with a target uncertainty value as a kind of validation. This is in full agreement with ISO 17025 that points to several ways of validation, among them systematic assessment of the factors influencing the result and assessment of the uncertainty of the results... [31]. In line with this is also a statistical modelling approach to the validation process that has recently been developed and exemplified as applied to in-house [32] and interlaboratory [33] validation studies. 

Eor substances that are not yet defined as priority substances and for which EQS are not finalised, these performance targets cannot be applied. However, the knowledge of the measurement uncertainty and the limit of quantification in relation to predefined targets is important for judging the fitness for purpose of the data (for analysis of trends, comparison of data sets, classification of water bodies for the achievement of good ecological status, for example). 

In some cases it may be useful to make a rough estimation of the measurement uncertainty of a method at the target concentration, for example, at the MRL of a veterinary drug, to help to determine whether the method will be tit for purpose before undertaking a full validation and measurement uncertainty estimation exercise. This can be done by applying the Horwitz formula to obtain an estimate applicable to inter-laboratory reproducibility data, or a suitably adjusted version for intra-laboratory data. " The Horwitz formula, as initially applied to interlaboratory (between-laboratory) reproducibility data R) in percentage, and with the concentration C expressed as a mass fraction, is ... 

Measurement errors in LT systems are not only caused by the LT, the rest of the system components also take influence in the global error. In this case we will study the influence of the reflectors on the measurement uncertainty. Two types of reflectors will be tested, conventional SMR reflectors, in which the error depends on the angle of incidence of the beam on the reflector similar to experiments of Takatsuji et al. [8] on the cat-eye s and reflectors with automatic tracking system (Active Target). 

Although there has been a move to requiring the demonstration of a target measurement uncertainty. 

As outliers as such are laboratories that must be scrutinized and reasons for their poor performance understood, it is not good practice to remove them from consideration as happens in a method performance study. Unless there is a target mean and target measurement uncertainty (standard deviation) against which the results of all laboratories are assessed, the organizers must make a decision as to the actions to be taken with results that appear to be outlying. There are two approaches. First, outlier tests can be applied such as Cochran s test for laboratory variances (if... 

The matrices and elements that are studied target international trade, health, environmental issues, or politics that are associated with between country issues, and where possible are drawn from real-life samples. Laboratories are given the freedom to choose the method, measurands, or components that are relevant to their interests, and are encouraged to use their routine measurement methods. Usually, each laboratory is asked to report, as well as the value of the measurand, an expanded measurement uncertainty within which the value of the quantity being measured is claimed to be with a stated probability. The laboratories are also asked to indicate the method used, whether or not they consider themselves to be expert in the analysis, and to what guides or standards they may be accredited. As with any interlaboratory proficiency study full anonymity of the laboratories is guaranteed. 

Precision Precision is the closeness of agreement between results obtained under specified conditions, and is usually expressed as a standard deviation or RSD. Depending on the conditions specified, contributions may appear as bias or precision. For example, the temperature effect may be viewed as a random variable if sufficient experiments are done allowing the temperature to vary. On the other hand, if temperature is controlled and measured any difference from the target temperature can be corrected for as a bias. The measurement uncertainty is reduced, but still contains a contribution from the measurement of the effect (bias). 

Targets for measurement uncertainty describe how accurate and precise the measurements need to be. Targets for identification confidence describe how certain one needs to be that the correct analyte has been identified. 

Establishing method fitness consists of showing that the targets for measurement uncertainty and identification confidence have been met. 

A method s limit is the point where the targets for acceptable measurement uncertainty or identification confidence can no longer be met. Given this definition, the empirical or top-down approach is preferable for describing method limits when... 

IAEA (2001) International target values 2000 for measurement uncertainties in safeguarding nuclear materials, STR-327, International Atomic Energy Agency, Vienna... 

Prom this formula for thin target, we find that the target density factor cancels out and thus the error due to uncertainty in the measurement of target thickness gets eliminated. However, the target thickness is used in the determination of the correction factor Ci. Depending upon the target thickness, the correction factor Cj can be calculated by either of the two methods. 

Validation To understand the performance of the instrument, including limitations. Measurement uncertainty for the instrument, and specifically for individual target materials, is required to assist in interpretation, that is, to determine what constitutes a significant difference between samples. The validation protocol should be developed in line with guidelines provided by the local accreditation body (e.g., the National Association of Testing Authorities, Australia, NATA [184,185]) while taking into consideration the relevance of... 

Figure 5 —Peak TOA dependence on (mass) for species detected as singly charged positive ions produced by electron impact in the mass spectrometer target = AI2O3 X=1064 nm Same conditions as for Fig. 4. Fitted slope gives r =550 50 K. Measurement uncertainties are ps ...

Figure 6 —Velocity distribution (peak normalized) for A1 (AI2O3) at 15 J cm X=I064 nm. Solid curve is based on a plasma gasdynamic model [3,4] using the parameters shown in the figure, where y is an effective heat capacity ratio used to model the expansion process subscript s refers to target surface condition, p the plasma, and b the molecular beam. Measurement uncertainties are v 1000 cm s" at 10 cm s" based on 5 ps channel time resolution at 47 9 cm density distribution < 0.05 arb. units.

The prediction of the size and permeability of the aquifer is usually difficult, since there is typically little data collected in the water column exploration and appraisal wells are usually targeted at locating oil. Hence the prediction of aquifer response often remains a major uncertainty during reservoir development planning. In order to see the reaction of an aquifer, it is necessary to produce from the oil column, and measure the response in terms of reservoir pressure and fluid contact movement use is made of the material balance technique to determine the contribution to pressure support made by the aquifer. Typically 5% of the STOMP must be produced to measure the response this may take a number of years. 

As in the previous experiments, at each epoch we would like to select a waveform (or really the error covariance matrix associated with a measurement using this waveform) so that the measurement will minimize the uncertainty of the dynamic model of the target. We study two possible measures entropy of the a posteriori pdf of the models and mutual information between the dynamic model pdf and measurement history. Both of these involve making modifications to the LMIPDA-IMM approach that are described in [5]. Since we want to minimize the entropy before taking the measurement, we need to consider the expected value of the cost. To do this we replace the measurement z in the IMM equations by its expected value. In the case of the second measure, for a model we have... 

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