Incorrect sampling error

The first two errors described above are summarily called the correct sampling errors (CSE) in both 0-D and 1-D sampling contexts. 

In contrast, the sampling process itself gives rise to three complementary so-called incorrect sampling errors (ISE), to be delineated in full as these constitute the main culprits with respect to all practical sampling if no action towards their elimination is taken. 

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Thus the TOS introduces both the correct and incorrect sampling errors, CSE and ISE. At all particnlar sampling stages, these combine to the total samphng error (TSE) ... 

A comparison of the specific setup of correct and incorrect sampling errors for 0-D versus 1-D sampling respectively is used to illustrate the specific process sampling issues. A schematic synopsis of the commonalities and differences involved is given in Figures 3.7 and 3.8. 

Figure 3.7 Sampling error relationships for the case of batch sampling (0-D). A core of correct sampling errors (CSE) is embedded in a cloak of incorrect sampling errors (ISE). Representative sampling must start by eliminating all ISE.

EAT factory acceptance test ISE incorrect sampling errors... 

Reported mercury values in the oceans determined since 1971 span three orders of magnitude, due at least in part to errors induced by incorrect sampling [62-64]. Olasfsson [65] has attempted to establish reliable data on mercury concentrations obtained in cruises in North Atlantic water. 

The sources of sampling error are constitutional error, distributional error, and error caused by use of the incorrect sampling technique [GARFIELD, 1989 MINKINNEN, 1987],... 

Field procedure error—misidentified or missed sampling points in the field the failure to use consistent sampling procedures gaps in field documentation the use of incorrect sampling equipment and sample containers incorrect sample preservation techniques or storage... 

Impact Analysis for Incorrect Sample Size Error... 

Condition (mix) a one-dimensional enclosed liquid or gas stream. Since a cross-streaim sample is impossible to obtain, giving the stream a more homogeneous cross section reduces the grouping and segregation error (GSE) and the impact of incorrect delimitation. It also reduces the impact of taking an incorrect sample. 

Again, as the sample size increases the SE decreases in proportion to the square root of the sample size and the CI narrows. Also, although the result for sample A is not obviously incorrect, in fact the sample is too small to use the large sample expression. Instead, a distribution known as the t distribution, which describes sampling error in small samples with quantitative data, should be used. The multiplier corresponding to the normal distribution z of 1 -96 depends on the sample size. The values of t are tabulated... 

One of the most important aspect of allergen detection is sampling, followed by preparation of the sample for analysis. Generally, the distribution of the allergen as contaminant in the food product is extremely heterogeneous, and for this reason an incorrect sampling procedure, which is one of the main sources of error, may lead to poor-quality results. To guarantee the representativeness of the sample, it is necessary ... 

Initially, whole blood, plasma and serum were the accepted indicators of Se exposure. However, selenium measurements have now been extended to many organs and other body fluids. Publications on Se analysis of biological samples are numerous, but it is evident that there have been incorrect, inaccurate and imprecise results reported. The main reasons for these have often been related to sampling errors, contamination, losses during handling, pretreatment, decomposition and steps in procedure. Vital information on sample collection, procedure, precision and use of certified material is rarely provided [7], Several interlaboratory comparisons of Se analyses have appeared, which focus on the use of certified material and other factors [80-82]. 

Also, systematic errors can tKCur during the calibration process. For example, if the standards are prepared incorrectly, an error will occur. The accuracy with which the standards are prepared depends on the accuracy of the gravimetric and volumetric techniques and equipment used. The chemical form of the standards must be identical to that of the analyte in the sample the state of oxidation, isomerization, or complexation of the analyte can alter the response. Once prepared, the concen-... 

Figure 7.1. Simulated interferogram sampled at equally spaced intervals (solid vertical lines) and unequally spaced intervals (dashed lines). The difference between the ordinate values of the correctly and incorrectly sampled interferograms is equivalent to noise superimposed on the true interferogram. The error is dependent on both the difference between the correct and actual sampling positions and the slope of the interferogram at each point.

There are several sources of irreproducibility in kinetics experimentation, but two of the most common are individual error and unsuspected contamination of the materials or reaction vessel used in the experiments. An individual may use the wrong reagent, record an instrument reading improperly, make a manipulative error in the use of the apparatus, or plot a point incorrectly on a graph. Any of these mistakes can lead to an erroneous rate constant. The probability of an individual s repeating the same error in two successive independent experiments is small. Consequently, every effort should be made to make sure that the runs are truly independent, by starting with fresh samples, weighing these out individually, etc. Since trace impurity effects also have a tendency to be time-variable, it is wise to check for reproducibility, not only between runs over short time spans, but also between runs performed weeks or months apart. 

Strictly speaking, monodisperse samples would be required for the determination of the Mark-Houwink coefficients. Since, however, the poly-dispersities of the nine individual fractions are only moderate (Mw/Mn 2) and since both Mw and [tj] are measured as weight averages with the same statistical weights, the error introduced by the incorrect treatment of the polydispersity could be neglected. 

This procedure (based on sample variance and covariance) is referred to as the direct method of estimation of the covariance matrix of the measurement errors. As it stands, it makes no use of the inherent information content of the constraint equations, which has proved to be very useful in process data reconciliation. One shortcoming of this approach is that these r samples should be under steady-state operation, in order to meet the independent sampling condition otherwise, the direct method could give incorrect estimates. 

If a sample does not represent the bulk system in the manner intended, if the sample s integrity is not maintained during transportation, or if the preparation schemes go awry and do not provide the intended product, then the analytical results to be reported will be incorrect regardless of whether the analytical method was performed without error. 

The effort to carry out all these balances is high, but it significantly increases the reliability of the results, that should be based not only on single measurements (analyses). Usually, incorrect data are only detectable on the basis of at least two independent values or balances. If various balances are found, often an error can be identified as a false measurement or analysis mistake and not a real failure. As far as possible, several samples should be taken during each experiment for improved reliability. For continuous operation under stationary conditions, the average of some measurements and analyses will be used (any tendency in the individual values shows that the stationary state is not yet achieved). In case of batch operation a consistent change with time confirms reasonable results (here, in the mass balance the decrease of the cell liquid by the sampling has to be considered). 

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