Laboratory testing precision

Veith. A. G.. A New Approach to Evaluating Inter-Laboratory Testing Precision, Polvmer r tmg./2. 113 (1993). 

As seen in Chapter 2, mixtures of hydrocarbons and petroleum fractions are analyzed in the laboratory using precise standards published by ASTM (American Society for Testing and Materials) and incorporated for the most part into international (ISO), European (EN) and national (NF) collections. We wiil recall below the methods utilizing a classification by boiling point ... 

Precision testing or laboratory testing CTs Laboratory and lest work in conjunction with high precision indicating instruments, integrating meters and also for the testing of industrial CTs Precision industrial meters (indicating instruments and recorders)... 

Laboratory tests, in which conditions can be precisely defined and controlled. 

Since weather varies from day to day, year to year, and place to place, no precise correlation exists between artificial laboratory weathering and natural outdoor weathering. However, standard laboratory test conditions produce results with acceptable reproducibility and in general agreement with data obtained from long-time outdoor exposures. 

The value of any analysis is judged by the characteristics of the sample as determined by laboratory tests. The sample used for the test(s) must be representative of the bulk material, or data will be produced that are not representative of the material and will be incorrect no matter how accurate or precise the test method. In addition, the type and cleanliness of sample containers are important if the container is contaminated or is made of material that either reacts with the product or is a catalyst, as the test results may be wrong. 

Intermediate precision is another measure of the performance of the method where samples are tested and compared using different analysts, different equipment, different days, etc. This study is a measure of interlab variability and is a measure of the precision that can be expected within a laboratory. Intermediate precision is not required if a reproducibility study has been performed. Table 6 lists the ranges and suggested acceptance criteria for evaluation of precision during method development. 

The basic criterion for successful validation was that a method should come within 25% of the "true value" at the 95% confidence level. To meet this criterion, the protocol for experimental testing and method validation was established with a firm statistical basis. A statistical protocol provided methods of data analysis that allowed the accuracy criterion to be evaluated with statistical parameters estimated from the laboratory test data. It also gave a means to evaluate precision and bias, independently and in combination, to determine the accuracy of sampling and analytical methods. The substances studied in the second phase of the study are summarized in Table I. 

An overview of the important characteristics of explosives is given in Chapter 1. With the advent of various modeling techniques, much information concerning any given explosive can be obtained by theoretically calculating its properties. This information is valuable but indicative as calculations predict performance, which an explosive may have under ideal conditions. In practise, such perfection is never achieved and it is a matter of practical importance to assess their properties experimentally under conditions more appropriate to their use. Such an assessment is usually made by a series of tests chosen to determine the performance of explosives under various conditions. While these tests are of considerable value, it must be remembered that no laboratory test or series of tests can predict precisely the performance of explosives which may be used for widely varying purposes. The ultimate test for all explosives is their performance in the field. 

Abnormal clearance may be anticipated when there is major impairment of the function of the kidney, liver, or heart. Creatinine clearance is a useful quantitative indicator of renal function. Conversely, drug clearance may be a useful indicator of the functional consequences of heart, kidney, or liver failure, often with greater precision than clinical findings or other laboratory tests. For example, when renal function is changing rapidly, estimation of the clearance of aminoglycoside antibiotics may be a more accurate indicator of glomerular filtration than serum creatinine. 

Efforts to develop modified Claus processes that will operate with low concentrations of sulfur in the feed gas have been previously mentioned. A similar system is being laboratory tested at IGT which does not require precise, instantaneous control of the oxygen/sulfur feed ratio. 

When using medical laboratories, physicians frequently assume that the results provided are accurate and precise. Those working in the laboratory environment know that this is true only within the constraints of the methods, technology and processes available. In this chapter we will explore how internal quality control (IQC) and external quality assurance (EQA) procedures can inform both the analyst and the physician about the limitations of laboratory testing and permit a more intelligent use of laboratory data, while at the same time indicating areas where improvement is required. 

What would the resulting Youden plots look like if the method was rugged If the method was not rugged If the laboratories were precise, but each was biased If the laboratories were imprecise, but accurate [See, for example, Youden, W.J. (1959). Graphical Diagnosis of Interlaboratory Test Results , Industrial Quality Control, 24(May), p. 24.]... 

Tablet hardness is a property that, when measured, destroys the sample. The destructive nature of the test, coupled with the variability of the test itself does not contribute to an incentive to test a large number of samples. Morisseau and Rhodes99 correlated the diffuse reflectance NIR spectra of tablets pressed at different pressures and subsequently tested the tablet hardness with an Erweka Hardness Tester. The tablet hardness, as predicted by the NIR method, was at least as precise as the laboratory test method. Kirsch and Drennen100 evaluated NIR as a method to determine potency and tablet hardness of Cimetidine tablets over a range of 1-20% potency and 107-kPa compaction pressure. Hardness at different potency levels was used to build calibration models using PCA/ principal component regression and a new spectral best-fit algorithm. Both methods provided acceptable predictions of tablet hardness.

Once a stability study is started, testing dates are defined by the testing frequency. Occasionally, however, most laboratories will experience difficulty testing precisely on the scheduled test date. An SOP therefore should describe the allowable time between the scheduled test date and the actual... 

Example 10 Comparison of two variances. A simplified analytical procedure is proposed for a routine laboratory test. It is necessary to determine not only whether the new procedure gives the same results as the old, i.e., whether the means of a duplicate set are the same, but also whether the precision of the new test is as good as the current test. The data for the two tests are as follows ... 

DETERMINING THE TYPE OF SOIL. Every soil cousists of mineral particles of varying sizes. The ratio of the particle sizes present in a soil largely determines the properties of the soil. The granulometric composition (texture) of a soil can he precisely determined hy laboratory tests (sieve and sedimentation analysis). Large particles are determined hy sieving and finer ones by sedimentation. The soil type is apparent from the ratio of the individual granulometric fractions. 

ISO 5725 (1986) Precision of test methods - Determination of repeatability and reproducibility for a standard test method by inter-laboratory tests. 

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