Representative sample, definition

In as much as the present TOS expose has specified clearly that reliable analytical information derives from reliable analytical results (data) , meaning analytical results exclusively stemming from representative samples and commensurate sampling plans, it stands to reason that any definition of data quality perforce must include reflections/reference to representative sampling. Thus it is crucial also to contemplate the specific origin(s) of any data set in the context of the TOS. 

The definition of the term representative sample is given in Section 4.1. In each case the representativeness should be regarded as being defined for the specific purpose. In environmental investigations it is impossible in practice to obtain one representative sample, except for the case of a composite sample for bulk analysis. It is, however, possible to obtain representative samples with a properly designed and optimized sampling plan (see Section 4.5.3). 

Even a cursory perusal of any analytical journal will demonstrate the increasing importance of trace and ultra-trace analysis. And as instrumentation continues to develop, the definition of the term "trace element" will undoubtedly continue to change. Covering the composition and underlying properties of freshwater and marine systems, Analytical Measurements in Aquatic Environments provides the basis for understanding both. It discusses all aspects of analytical protocols from the handling of representative samples to the metrological evaluation of specific steps and whole procedures.The book covers ... 

Ash analytical methods may thus be used to test for evidence of protein-based matter including waterfowl down and feathers. But the characterization or even identification of bird species can hardly be definitely determined on the basis of chemical element percentage alone. One reason is the difficulty of collecting a chemically representative sample from a fairly non-homogeneous natural product. 

It is important to understand the principles of sampling and be aware of the precautions that are necessary to obtain a representative laboratory sample. Definitions of the terms increment, sample, spot sample, composite sample and laboratory sample are given in the Glossary. Figure 6.1 illustrates how they are related. 

Standard definition television (SDTV) This term is used to signify a digital television system in which the quality is approximately equivalent to that of NTSC. This equivalent quality may be achieved from pictures sourced at the 4 2 2 level of ITU-R Recommendation 601 and subjected to processing as part of the bit rate compression. The results should be such that when judged across a representative sample of program material, subjective equivalence with NTSC is achieved. Also called standard digital television. 

Are random samples representative by definiticm Are representative samples random by definition What condition must exist for each of tiiese questions to be answered affirmatively ... 

Table 1 is a representative sample of what is typically available. Different suppliers may have capabilities greater or less than those indicated. Additionally, there is no generally established definition of primary or certified standards, and these terms can be used differently by different suppliers. See also Fig. 1. 

The role of speeding as a direct crash cause was probably first analyzed in a detailed and comprehensive manner by Treat et al (1977). In this study, described in detail in Chapter 17, a representative sample of more than 2,000 police-reported crashes was analyzed by crash investigators at the crash sites, and 420 of them were further analyzed by multidisciplinary teams. A cause was defined as an event or action whose absence would have prevented the crash, all other things being equal. Furthermore, a human cause was cited if the causal behavior was a deviation from the normal or expected behavior of the average driver. Thus, speed would not be cited in a crash of a speeding vehicle imless the speed deviated from the speed expected at that site under the conditions that prevailed and the crash would not have occurred had the speed been as expected. With this approach to causation, the study estimated excessive speed to be a definite cause in 7-8 percent of the crashes and a probable cause in an additional 13-16 percent of the crashes. 

Also, it would be exceedingly rare that we are interested in the contaminants contained in the specimens themselves. These have been removed from the field and in most cases will be disposed of by the laboratory, not returned to their original locations. An assumption that underlies the method as described is that the sample of specimens is representative of conditions in the field, and statistical methods can be employed in attempt to ensure that a representative sample has been obtained. But in reality this methodology can only ever give definitive information about the individual specimens themselves. For practical reasons, soil specimens are relatively small in lateral extent and mass (they are unlikely to be greater than about 10 cm in diameter and 2 kg mass). Any conclusions about the greater mass of soil left behind have to be inferred using statistical methods. 

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