Measurement limit of reliable

Systematic error is also known as bias. The bias is the constant value difference between a measured value (or set of values) and a consensus value (or true value if known). Specificity is the analytical property of a method or technique to be insensitive to interferences and to yield a signal relative to the analyte of interest only. Limit of reliable measurement predates the use of minimum detection limit (MDL). The MDL... 

The acceptance of the laboratory characterization of tests will be based on the kinds of information usually included in a methods development paper. FSIS suggests that supporting data be submitted in a publication format or, as a reprint, if the information has already been published. The information should include the purpose of the test, the analyte and matrix (including the species), a summary of the technique, its unique features, and performance characteristics such as limit of detection, limit of reliable measurement, and precision. The performance near regulatory decision points is of particular importance. As would be expected of a method development paper, the reagents, equipment, and the details of the method must be thoroughly described. 

Evaluation, characterization, and testing of a particular analytical method is necessary to ensure the intended use of the method is met. In general, this process requires the determination of intra-and interlaboratory studies for precision and bias, method detection limits, matrix effects, interferences, limits of reliable measurements and ruggedness of the method. Before the EPA commits time and resources for an in-depth evaluation study, the developer must meet certain developmental criteria or justify why they were not met. The developer must also clearly define all necessary reagents as well as the underlying basis of the immunoassay. 

Analytical methods have two types of characteristics—scientific and practical. The scientific characteristics determine the reliability of the analytical data the practical characteristics determine the utility of the method. The scientific attributes of a method include such things as accuracy, precision, specificity, and limit of reliable measurement the practical attributes... 

The final property of methods which we will consider here is the limit of reliable measurement. This is the quantitative aspect of the common limit of detection—the smallest amount or concentration of a substance which provides a measurable response by a specified method. Although the limit of detection is a widely used term, particularly by advertisers of scientific instruments, it and related terms are not well defined, accepted, or understood. In fact, this characteristic, although intuitively simple, may not be a stable attribute of analytical methods, but more a function of external influences such as laboratory environment or electronic fluctuations. 

Too often the term "sensitivity" is misapplied to the concept of limits of detection or determination. Sensitivity is the slope of the response curve—the change in response per unit measured— as in almost all other branches of measurement. The concept of least measurable amount is better described as determinability, or limit of reliable measurement, and least detectable amount as detectability, or limit of detection. 

Most of the false negative reports (reporting zero when dioxin was added) occurred at levels of 9 ppt and below. The only false negatives at levels above 9 ppt, oddly enough, occurred in the standard series (no interference). No false negatives were reported in the beef fat and human milk series above 9 ppt. Therefore, examination of the data by inspection results in an estimate of about 10 ppt for the limit of reliable measurement in... 

The limit of reliable measurement of the ELISA was 21 ppb. The limit of reliable measurement Is a calculated concentration that Is approximately the mean plus two standard deviations, multiplied by two, of a negative control sample (12,1 ). This measurement Is probably more meaningful than a conventional limit of detection because It provides a conservative and statistically well supported estimate of the operating characteristics of the assay, obtained... 

Oppenheimer, L., Capizzi, T. R, Weppelman, R. M., and Mehta, H., Determining the Lowest Limit of Reliable Assay Measurement, Anal. Chem. 55,... 

The most critical part of the method selection is determining the relative merits of seemingly diverse HPLC separations. Unfortunately, there is no standard against which all HPLC methods for vitamins are presently compared. However, there are indicators of assay reliability for which the analyst should look. These include measures of precision, accuracy, and reproducibility recoveries from spiked food samples linearity of calibration limits of detection measures of peak purity comparisons with existing recognized methods and results of collaborative or interlaboratory trials (9,10). 

Another laboratory value that is often obtained in these exposures is serum pseudoeholinesterase. Serum pseudocholinesterase activities are often assessed as normal in children because the reference standards may not be reliable when assessing children. To add to the complexity, the normal range of serum cholinesterase activity is wide (Sofer et al, 1989). Authors have described the limitations of this measurement in determining therapy for children. In fact, it is recommended that a therapeutic and diagnostic trial of atropine should be given whenever there is any possibility of intoxication with these chemicals (Sofer et al, 1989). 

The choice of the temperature is governed by the conditions of reliable measurement of the primary signal. Am/At. The lower limit of measuring this signal depends on the stability of the analyser baseline. According to experimental estimates, with the devices, STA 429 and STA 449, the variations in blank experiments reach 0.05-0.07 pg s. Therefore, it is desirable that the measured signal should exceed at least 0.2-0.3 pg (overestimation of the... 

This discussion will be restricted to estimation of DL s appropriate for routine application of methods in which a calibration function relates a signal to concentration for a series of standards. No attempt will be made to evaluate the merits of various terms such as limit of quantitation, method detection limit, lower limit of reliable assay measurement, and others. For a discussion of those Issues, the reader is referred to the articles cited here and to other papers from this symposium. 

Confidence intervals are essential for component strength and life prediction methods, and for methods verification in this program. Verification of the life prediction methods will be accomplished by comparing observed confirmatory specimen lives with predictions. There will be some uncertainty in the predictions, due to the size and number of specimens tested to generate the life prediction model parameters. Confidence intervals on the predictions will help quantify this uncertainty, and thereby determine (1) the expected deviation between measured and calculated lives, or (2) if the deviation is a result of modeling inaccuracies. Confidence intervals are also needed for component design to define the lower limits of reliable component operations. 

In safety, we must realize that all of our measures have limitations on their reliability, and that all measures are subject to manipulation. It is important that we understand the limitations of each measure and we take these limitations into account when making decisions based on the measurements. In the following chapters we will discuss the reliability of a variety of measures of safety. 

I. This includes cases where the independent variable is time and the dependent variable might represent some physical parameter in a manufacturing process which must be held between some limits. As another example, it might represent various types of reliability measurements of a physical parameter where the inde-... 

Finally, for situations in which it is not clear that exposure is and will continue to be below the limit values, a detailed survey with a measurement strategy is required. The methods used are based mostly on instruments for sampling the environment in order to obtain reliable measurements of workplace air concentrations. In general, the measurement strategy must consider the most efficient use of resources for the purpose of obtaining quantitative data on exposures by having a clear idea of what the data will be used for or whether it meets the specified need. For example, if the data pertain to peak exposures, these peaks have to be assessed according to the STEL requirements, if any. 

The value of the magnetic hyperfine interaction constant C = 22.00 kHz is supposed to be reliably measured in the molecular beam method [71]. Experimental data for 15N2 are shown in Fig. 1.24, which depicts the density-dependence of T2 = (27tAv1/2)-1 at several temperatures. The fact that the dependences T2(p) are linear until 200 amagat proves that binary estimation of the rotational relaxation rate is valid within these limits and that Eq. (1.124) may be used to estimate cross-section oj from... 

The limit of detection (LOD) (see Figure 2.6) is defined as the smallest quantity of an analyte that can be reliably detected. This is a subjective definition and to introduce some objectivity it is considered to be that amount of analyte which produces a signal that exceeds the noise by a certain factor. The factor used, usually between 2 and 10 [11], depends upon the analysis being carried out. Higher values are used for quantitative measurements in which the analyst is concerned with the ability to determine the analyte accurately and precisely. 

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