Measurement inter-laboratory studies

Lee and Chau [66] have discussed the development and certification of a sediment reference material for total polychlorobiphenyls. Alford Stevens et al. [49] in an inter-laboratory study on the determination of polychlorobiphenyls in environmentally contaminated sediments showed the mean relative standard deviation of measured polychlorobiphenyl concentrations was 34%, despite efforts to eliminate procedural variations. Eganhouse and Gosset [67] have discussed the sources and magnitude of bias associated with the determination of polychlorobiphenyls in environmental sediments. Heilman [30] studied the adsorption and desorption of polychlorobiphenyl on sediments. 

The factor 2I/Z is based on the fact that r and R are related to the difference between two measurement results. For distributions which are approximately normal and in the case of not too small a number of measurements, the factor f does not vary much from 2 and one can use the approximate value of 2.8 for f-2I/2. Because in practice the true repeatability and reproducibility standard deviations are not known, they are replaced with estimated values sr and sR from the inter-laboratory study and one obtains then ... 

An international inter-laboratory study recently compared quantitative methods used for measuring short chain (C10-C ) PCAs [70]. In this study, the samples to be quantified consisted of a standard solution of a commercially available PCA product containing 70% chlorine by mass (PCA-70), a synthetic PCA mixture consisting of purified products derived from the chlorination of 1,5,9-decatriene (PCA-1) and two fish sample extracts. The fish samples consisted of a cleaned up extract (lipid-free) of muscle tissue from a yellow perch fish, collected at the mouth of the Detroit River at Lake Erie, in 1995. All participating labs were asked to quantify the PCA-1 and PCA-70 mixtures and at least one fish extract against a primary standard solution which contained a known concentration of a second short chain commercial PCA product containing 60 mass % chlorine (PCA-60) and, if desired, by using other commercially available C10-C13 PCA mixtures. 

Work is underway to standardize the test method described here as a new ASTM standard. An Inter-Laboratory Study (ILS) is proposed to include at least nine each of gasoline and diesel Tier 2 class materials containing sulfur levels between <10 and 80 mg/kg in gasoline and between <10 and 80 mg/kg in diesels. Some blind National Institute of Standards and Technology (NIST) Standard Reference Materials (SRM) and solvent blanks are also plaimed for the cross check. The ILS will follow a protocol of an initial analysis of a set of samples and solvent blanks, and after an elapsed time of at least 12 h but no more than 72 h, a second set of measurements on the same set of samples and blanks will be completed. We expect this ILS to be completed by the end of2005. 

Measurement Uncertainty Based on Inter-laboratory Study Data... 

Stickel JJ, Knutsen JS, Liberatore MW, Luu W, Bousfield DW, KUngenberg DJ, Scott CT, Root TW, Ehrhardt MR, Monz TO. (2009). Rheology measurements of a biomass slurry an inter-laboratory study. RheolActa, 48(9), 1005-1015. 

The results ofthe inter-laboratory study showed that the exposures produced only minor ehanges in the measured thermoanalytical properties. The materials tested were generally stable under the outdoor and laboratory exposure conditions. In the ease of TG analysis of the pyrolyzable organic constituents, it was found that the method showed rather good within- and between-laboratory variability. The number of participants in the d5mamic mechanical/TPA analysis was limited hence, no conclusion was made regarding the variability within and between laboratories. In the ease of... 

Methods of analysis also differ. The two analytical techniques most often employed are atomic absorption spectrometry and anodic stripping voltammetry. One inter-laboratory study using a (supposedly) homogenized tooth powder showed that the measurements obtained from different laboratories varied very significantly, with the results ranging from 4 to 15 iUg/g (Stack and Delves, 1982). However, subsequently there has been a suggestion that the tooth powder was not adequately homogenized, and this... 

The sensitivity achieved (LOD) is not normally presented. It is recognized that different laboratories determine dissimilar values for this parameter and even within a laboratory the repeatability of the LOD is low. Most often, the lowest validated concentration gives an impression about the lowest levels that can be analyzed generally with acceptable results. A measure of selectivity is the intensity of blank results. This intensity is discussed by the participants of inter-laboratory validation studies. However, results are not reported and limits are not defined by CEN TC 275. The results of method validations of the several multi-residue/multi-matrix methods are not reported in the same way, but newer methods with limited scope generate analogous tables with validation results (as an example, see Table 7). 

The largest commercially available datasets are the Physical Properties (PHYSPROP) and AQUASOL databases ca. 6000 compounds in each database). The AQUASOL database has been published as a book. Furthermore, two relatively large sets of aqueous solubility data models were used in many other studies.Data from the AQUASOL database had an interlaboratory variation of about a = 0.49 log-units (as estimated for A=1031 molecules).Moreover, large inter-laboratory errors mask the influence of temperature, and differences as large as AT = 30 °C do not increase this error. In-house models developed at pharmaceutical companies could be based on similar or even larger numbers of measurements. For example, about 5000 molecules were used to develop a model at Bayer Healthcare AG. " ... 

These assays, which have been standardized and validated at InterceU AG s Ghni-cal Immunology Laboratory, enable reliable measurements of epitope-specific T cell responses induced by vaccination. All assays were performed in compliance with Good Laboratory Practice (GLP)/Good Clinical Practice (GCP) requirements. Standardization of the blood cell isolation procedure at the different investigational sites led to a high rate of evaluable assays. However, due to the lack of inter-laboratory standardization of T cell assays, comparison of the results of this study with published data from similar trials is difficult. Cryopre-served blood cells were used, which may have resulted in a possible underestimation of T cell responses compared with assays that utilize fresh blood. 

Kent and Smith (1987) reported the results of an inter-laboratoiy study on measmement of colom standards. They came to the obvious and important conclusion that in order to transfer and compare colour data from one laboratory to another, which is certainly necessary when colour is being used as a buying criterion, the measuring system and the colour standard have to be carefully defined. Most instrument manufacturers will provide details of best practice with respect to how the instrument and its standards should be maintained. 

Guillard, O. and Pineau, A. (1986) The measurement of plasma aluminium by the worldwide inter-laboratory quality control aluminium study distribution and utilisation of the results. In Taylor, A. (Edit) Aluminium and other Trace Elements in Renal Disease, Bailliere Tindall, London, p. 283. 

The basics of inter-laboratory (between laboratories) and intra-laboratory (within a laboratory) studies have been summarized in the ISO-5725 standard (Feinberg 1995). Recognizing that measurements are often laborious to undertake, examples cited in the standard have often only three measurements per test and only four laboratories. A single reported measurand, y, is the sum of the true value, x, a component of the accuracy, B, and a component of random variability during any measurement, e (within the laboratory variance) ... 

It is possible to take up the problem from the other end and to declare the reproducibility of the procedure, i.e. the inter-laboratory standard deviation jr, as the measurement uncertainty ( top-down procedure). If the same analytical procedure is performed in numerous laboratories at the occasion of a collaborative study it can be assumed that all possible influences add to the inter-laboratory standard deviation which finally is calculated from all data. If no interlaboratory test was performed, it is only the own intra-laboratory standard deviation which is known, a value that may be too small and thus too optimistic, especially when it is necessary to compare the own results with the ones from other laboratories (suppliers, customers, authorities, competitors). 

The lack of comparability in the type or part of tooth analysed, differences in methods of analysis, and possible inter-laboratory differences make it impossible to know how lead levels from one study compare with those from another study, unless there is some secondary measure of lead burden available for at least part of the population. 

Contact angle measurement is commonly used to characterize a surface and to study various wetting and de-wetting phenomena While the measurement is simple, the interpretation is not. This point has been noted by many surface investigators in the past, e.g.. Pease in 1945 [25], Morra et al. [26] in 1990, Kwok and Neumann [27] in 1999 and more recently by Marmur [28] as well as Strobel and Lyons [29]. Prior to data interpretation, one has to make sure that the measurement apparatus and procedures are impeccable. Over the years, many have voiced concerns over surface preparation and conditioning, measuranent procedure and technique, and data analysis [26,30-35]. It is therefore imperative for the community to have a set of common measurement protocol or guideline, so that inter laboratory data can be compared. Discrepancy in conclusion can be rationalized without concerns of experimental setups or procedures. 

In a protocol about collaborative studies [10] it is also considered what is called preliminary estimates of precision. Among these the protocol defines the total within-laboratory standard deviation . This includes both the within-run or intra-assay variation (= repeatability) and the between-run or inter-assay variation. The latter means that one has measured on different days and preferably has used different calibration curves. It can be considered as a within-laboratory reproducibility. These estimates can be determined prior to an interlaboratory method performance study. The total within-laboratory standard deviation may be estimated fi-om ruggedness trials [10]. 

The accuracy of exposure assessment is determined by systematic and random errors in the assessment. For quantitative exposure assessments, important sources of error include measurement errors (i.e. from laboratory and field monitoring techniques), as well as variations in exposure over time and space. For qualitative exposure proxies (e.g. self-reported past exposures, occupational histories or expert evaluations), the most important sources of error are recall bias (systematic differences in exposure recall between cases and controls) and random error, expressed in terms of intra- and inter-rater agreement. Although systematic errors can result in serious misinterpretations of the data, especially due to scaling problems, random errors have received more attention in epidemiology because this type of error is pervasive, and its effect is usually to diminish estimates of association between exposure and disease. The magnitude of random errors can be considerable in epidemiological field studies. 

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