Intermediate measurement precision

NOTE 2 The specified conditions can be, for example, repeatability conditions of measurement, intermediate precision conditions of measurement, or reproducibility conditions of measurement (see ISO 5725-2 1994). NOTE 3 Measurement precision is used to define measurement repeatability, intermediate measurement precision, and measurement reproducibility. 

Intermediate measurement precision (IMP), which is the set of conditions that includes the same measurement procedure, same location, and replicate measurements on the same or similar objects over an extended period of time. This specification allows for other conditions (e.g., different reagent lots) involving changes and... 

Figure 4,2 The repeatability and intermediate measurement precision IMP) of a robotic HX-MS apparatus. The study is based on replicant measurements of bovine ubiquitin deuterium uptake after 30s immersion in D O. (a) The peptide map of ubiquitin, comprising 29 peptides (100% protein coverage) observed in 39 analyzed peptide ions, used for the HX-MS analyses (see footnotes 2, 3 and Ref [27]). (b) The average fractional D uptake observed for each of the 39 analyzed peptide ions. As shown in the key, each symbol presents the average of 20 measurements conducted on Day 1, 2, and 37. Bars on each symbol indicate the standard deviation (SD) when it exceeds the symbol size, (c) Repeatability and IMP for each peptide set, plotted as the SD of the D fraction measurements obtained for each peptide. The horizontal solid line in each group indicates the mean SD of the peptide set (780 measurements)...

Table 4,1 Repeatability and intermediate measurement precision observed during robotic, proteolytic fragmentation HX-MS measurement campaigns... 

Description Measurement precision is usually expressed numerically by measures of imprecision, such as standard deviation, variance, or coefficient of variation, under the specified conditions of measurement. When a measurement precision is given, it is important to specify the conditions. These conditions can be, for example, repeatability condition of measurement, intermediate precision condition of measurement, or reproducibility condition of measurement (see ISO 5725-3 1994 and see below). The measurement precision is used to define measurement repeatability, intermediate measurement precision, and measurement reproducibiUty. In the VIM, it is mentioned that sometimes measurement precision is erroneously used to indicate measurement accuracy. 

Accuracy (Trueness and Precision) of Measurement Methods and Results - Part 3 Intermediate Measures of the Precision of a Standard Measurement Method , ISO 5725-3 1994, International Organization for Standardization (ISO), Geneva, Switzerland, 1994. 

International Organization for Standardization (ISO), Statistical methods for quality control, Vol. 2, 4th Edition, Accuracy (trueness and precision) of measurement methods and results - Part 3 Intermediate measures of the precision of a standard measurement method, ISO 1994(E), 5725-3. 

Between-run, interbatch precision or intermediate precision, which measures precision with time and may involve different analysts, equipment, reagents, and laboratories... 

ISO 5725-3 1994 Accuracy (trueness and precision) of measurement methods and results—Part 3 intermediate measures of the precision of a standard measurement method... 

Precision should be measured using a minimum of five determinations per concentration. A minimum of three concentrations in the range of expected concentrations is recommended. The precision determined at each concentration level should not exceed 15 % of the coefficient of variation (CV) except for the LLOQ, where it should not exceed 20 % of the CV. Precision is further subdivided into within-run, intrabatch precision or repeatability, which assesses precision during a single analytical run, and between-run, interbatch precision or reproducibility, which measures precision with time, and may involve different analysts, equipment, reagents, and laboratories. Since it is not always easy to obtain data about the reproducibility in the strict sense it often makes sense to use intermediate precision this expresses within-laboratories variations on different days, by different analysts, and on different equipment, etc. [60],... 

Part 3 1994 — Intermediate measures of the precision of a standard measurement method. 

Precision is defined as the measure of how close the data values are to each other for a number of measurements under the same analytical conditions . Taken together with accuracy, precision indicates how close an analyst will be to 50 mg (see above) on repeated measurements. Precision includes three sub-sections repeatability, intermediate precision, and reproducibility. 

The ISO 5725 provides a procedure for obtaining intermediate measures of precision, basic methods for the determination of the tmcmess of a measurement method, the determination of repeatability and reproducibility of a standard measurement method. 

Definition Measurement precision under a set of intermediate precision conditions of measurement (Figure 7.3). 

Diffusivity and tortuosity affect resistance to diffusion caused by collision with other molecules (bulk diffusion) or by collision with the walls of the pore (Knudsen diffusion). Actual diffusivity in common porous catalysts is intermediate between the two types. Measurements and correlations of diffusivities of both types are Known. Diffusion is expressed per unit cross section and unit thickness of the pellet. Diffusion rate through the pellet then depends on the porosity d and a tortuosity faclor 1 that accounts for increased resistance of crooked and varied-diameter pores. Effective diffusion coefficient is D ff = Empirical porosities range from 0.3 to 0.7, tortuosities from 2 to 7. In the absence of other information, Satterfield Heterogeneous Catalysis in Practice, McGraw-HiU, 1991) recommends taking d = 0.5 and T = 4. In this area, clearly, precision is not a feature. 

The precision of an analytical procedure expresses the closeness of agreement (degree of scatter) between a series of measurements obtained from multiple sampling of the same homogeneous sample under the prescribed conditions. Precision may be considered at three levels repeatability (within run) intermediate precision (over time) and reproducibility (inter-laboratory). 

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