Accuracy, Precision, and Sensitivity

Sensitivity is the measure of the smallest amount that can be reliably measured. An instrument that can measure microgram (0.000001 g) quantities is much more sensitive than one that can only measure milligrams (0.001 g). Precision is thus an important limit to sensitivity. If the uncertainty, or imprecision, of a measurement is 0.0005 g, then the instrument is incapable of reliable microgram (0.000001 g) measurements, but can easily measure milligram (0.001 g) quantities. 

Although it might seem paradoxical, precision is generally the most important 

Moreover, if the measurements are precise, an analysis can be made of standard 

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Quality of analytical equipment specificity, accuracy, precision, and sensitivity of measuring and analyzing equipment determine the reliability of test results. 

Oishi 1990) however, the data are very limited. More information on the accuracy, precision, and sensitivity of these methods is needed to evaluate the value of using the levels of di-ra-octylphthalate and its metabolites (particularly in urine) as indicators of exposure. The lack of data for these methods makes it difficult to assess whether these methods are sufficiently sensitive to measure levels at which health effects might occur, as well as background levels in the population. 

The levels of accuracy, precision, and sensitivity noted for acid and ester recovery from Piedmont and Coastal soils are considered adequate to measure and detect silvex residues associated with the control of aquatic weeds. Similarly, the recovery of ester from Florida muck is judged to be acceptable down to 100 p.p.m. However, free acid recovery from muck is considered inadequate on all of these points. 

Together with details of sample preparation and storage, an appropriate analytical method of known accuracy, precision, and sensitivity must be available for the quantification of the substance in the test solution and in the biological material. If these are lacking it is impossible to determine a true BCF. The use of radiolabelled test substance can facilitate the analysis of water and fish samples. However, unless combined with a specific analytical method, the total radioactivity measurements potentially reflect the presence of parent substance, possible metabolite(s), and possible metabolized carbon, which have been incorporated in the fish tissue in organic molecules. For the determination of a true BCF it is essential to clearly discriminate the parent substance from possible metabolites. If radiolabelled materials are used in the test, it is possible to analyse for total radio label (i.e. parent and metabolites) or the samples may be purified so that the parent compound can be analysed separately. 

In order to achieve the optimum accuracy, precision, and sensitivity, most quantitative analyses are performed by using high-performance thin-layer chromatography (TLC) plates and direct quantification by means of a modern optical densitometic scanner with... 

Accuracy, precision, and sensitivity are very loosely used terms, generating considerable confusion. Obviously, results of EIA cannot be meaningfully interpreted nor can theoretical considerations be made if such important basic concepts are not clearly distinguished. Unfortunately, this confusion persists even in advanced theoretical treatments or in data processing. 

An understanding of some of the basic vocabulary and principles employed in archaeological chemistry is essential to understanding this field of study. In the following paragraphs a brief discussion of matter and energy includes these relevant concepts. This is followed by a consideration of measurement issues and the very small quantities of elements, isotopes, and molecules we often have to measure in the lab. Finally the meaning of accuracy, precision, and sensitivity provide perspective on the results obtained from scientific instruments. 

Barrie and Prosser [2] provide a discussion on accuracy, precision, and sensitivity issues related to measurements using IRMS instruments. 

The matrix effect is one of the main drawbacks of LC—MS/MS methods, as widely reported in the literature [16,22—26]. It appears as a consequence of fhe influence of coextracted matrix components on analyte ionization in atmospheric pressure ionization (API) interfaces. The matrix effect t)q5ically results in an important loss of sensitivity, due to the ionization suppression from the coextracted components hampering the analyte quantification. Although less frequent, enhancement of the analyte signal can also occur. This imdesirable effect causes a loss of method accuracy, precision, and sensitivity, leading to incorrect quantification and can also cause problems in the confirmation process [16,24,25]. The matrix effect depends on each particular analyte—sample matrix combination and the API source of the instrument, commonly ESI or APCI. As an example. Figure 12.1 shows absolute matrix effects for... 

Thermometers—Calibrated liquid-in-glass thermometers of suitable range with subdivisions and maximum scale error of 0.1 C (0.2 F) or any other thermometric device of equal accuracy, precision and sensitivity shall be used. Thermometers shall conform to the requirements of Specification E 1. 

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