Between-laboratory reproducibility

The precision of an analytical method is a measure of the variability of repetitive measurements. Contributions from numerous sources affect precision, but the major components are within-laboratory (repeatability) and between-laboratory (reproducibility) variations. Precision is expressed as the relative standard deviation (or CV)... 

The precision of recovery is determined under repeatability and reproducibility conditions. The more important between-laboratory reproducibility is calculated as relative standard deviation (RSDr) and compared with the RSDr, which is estimated from the Horwitz equation using the same analyte concentration. For good methods this ratio should be about 1, but a method will usually be accepted if the ratio is not larger than 2. 

Between-laboratory reproducibility should be obtained by different operators... 

Repeatability Within-laboratory reproducibility Between-laboratory reproducibility Same L, T, A, I Same L different T I and A may be different Different L, T, A, I... 

If it is not possible to involve additional laboratories for the determination of the between-laboratory reproducibility, then the within-laboratory reproducibility may be used to get an estimate of the between-laboratory reproducibility. The reproducibility of the method may be dependent upon the mass fraction of the analyte in the test sample. It is therefore recommended, when studying the reproducibility, to investigate whether a relation exists between concentration and reproducibility. The measurement series should be greater than 8. 

Many LC users are curious about the precision they can expect from an analysis. This question is often answered with specifications concerning flow rate precision, injection volume precision, and so forth. However, the precision of the analysis is influenced by all of the variables in the HPLC system, including operator error. Often within a laboratory, the precision of the LC analysis is within 1%. However, the larger question concerns the between-laboratory reproducibility of analyses. 

Number of laboratories i Mean Repeat standard Between laboratory Reproduce stan- ... 

The ensuing limited within- and between-laboratory reproducibility of the Draize rabbit eye test [5, 21-24],... 

Extensive reviews concerning the opportunities for the development of in vitro sensitization methods already exist [41-44], These reviews show that essentially all of the methods address one or other of the key mechanistic steps in the induction of skin sensitization—and these are nicely represented in the OECD adverse outcome pathway description [45], From this large body of work, three methods have emerged whose initial promise has been substantiated by demonstration not only of their predictive merits but also by verification of their robustness in terms of inter-laboratory transferability and within and between laboratory reproducibility [46]. The three methods are the direct peptide reactivity assay (DPRA) [47, 48], KeratinoSens [49, 50], and the human Cell Line Activation Test (h-CLAT) [51-53]. The first of these, the DPRA, addresses the question of chemical reactivity, the second investigates an aspect of keratinocyte activation... 

Standard protocols have been developed for methods with and without metabolic activation (S9 liver fraction), and their transfer-ability, within-laboratory reproducibility, and between-laboratory reproducibility [89, 90] have been evaluated. 

The main advantage of the modular approach is to make validation projects more flexible and more efficient. In addition, there is a labor reduction in terms of cost and time [18]. In particular, the aspects of between-laboratory reproducibility and predictive capacity are separated. Moreover, the modular design is suitable for prospective validation, retrospective validation, or a combination of both. 

The distribution of a limited number of microbes within a solid matrix is essentially inhomogeneous, i.e. for a certain level of intake, differences due to the distribution of the microbes will appear. The more microbes that have been introduced into the matrix, the less these differences will be important and the lower the sample intake will be where differences appear. The theoretical distribution of the microbes in the sample is described by a Poisson distribution [29,30]. The RIVM group, which developed these materials, used a modified Cochran s dispersion test to evaluate the variation within a single capsule and between capsules. In fact overdispersion (more inhomogeneity than theoretically expected) has been noticed for nearly all RMs and CRMs produced [31]. The certification trial revealed that it had no influence on the outcome of the interlaboratory certification study as the between-laboratory reproducibility largely covered this overdispersion factor. 

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 ... 

Between laboratory reproducibility. All labs observed the same tendencies for all parameters with or without preconditioning. Significant diveigences remain between laboratories for most of the parameters tested, and reproducibility was improved by preconditioning. 

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