Repeatability limit

Repeatability limit The value less than or equal to which the absolute difference between two test results obtained under repeatability conditions may be expected to be with a probability of 95%. 

Repeatability Standard Deviation Repeatability Limit r Reproducibility... 

Diesel cetane number reproducibility concerns usually develop whenever motor cetane numbers differ by more than one number. The reproducibility variation arises due to operator and engine differences. The typical reproducibility variance accepted by ASTM will change with increasing cetane number. The following reproducibility and repeatability limits have been established by ASTM for method D-613. 

Average Cetane Number Level Reproducibility Limits, Cetane Number Repeatability Limits, Cetane Number... 

Repeatability limits pertain to the difference between two test results obtained by the same operator for the same test fuel under constant operating conditions. If test values fall outside of these limits, the repeatability is considered poor. 

This is a useful check of day-to-day duplicated results. If the difference is greater than the repeatability limit, r, it is advisable to perform another experiment and test further (see ISO 1994). 

In chapter 2 I introduced the statistics of repeated measurements. Here I describe how these statistics are incorporated into a quality control program. In a commercial operation it is not always feasible to repeat every analysis enough times to apply t tests and other statistics to the results. However, validation of the method will give an expected repeatability precision (sr), and this can be used to calculate the repeatability limit (r), the difference between duplicate measurements that will only be exceeded 5 times in every 100 measurements. 

ISO uses two terms, trueness and precision , to describe the accuracy of a measured value. Trueness refers to the closeness of agreement between the average value of a large number of test results and the true or accepted reference value. Precision refers to the closeness of agreement of test results, or in other words the variability between repeated tests. The standard deviation of the measured value obtained by repeated determinations under the same conditions is used as a measure of the precision of the measurement procedure. The repeatability limit r (an intra-laboratory parameter) and the reproducibility limit R (an inter-laboratory parameter) are calculated as measures of precision. Again, precision and trueness together describe the accuracy of an analytical method. 

The parameters describing the scattering of a test result under repeatability and reproducibility conditions are the corresponding standard deviations. The repeatability limit, "r , is the within-laboratory precision and describes the maximum expected value of the difference between two individual test results obtained under repeatabil-... 

The difference between two individual measurement results, which an analyst obtained on the identical sample material with the same instrument within the shortest time span possible, will on average not exceed the repeatability limit r more than once in 20 cases, provided the measurement procedure has been correctly carried out. 

From the results obtained the repeatability standard deviation Sr as well as the repeatability limit r can be calculated on a 95 % probability level according to Eq. (10-13). 

Another immortalized rat brain capillary endothelial cell line is used in some labs, called GPNT. This cell line is obtained from GP8 cell line (Greenwood et al. 1996) by re-transfection with the plasmid pcDNA3-RSV and repeated limiting dilution cloning of the... 

The repeatability limit is calculated using the following formula ... 

A repeatability limit of 0.27 is obtained using the data in this example. The analyst can state that, at the 95% confidence level, two results differing by 0.27 are statistically significantly different. 

It is often necessary to estimate the spread of results obtained in different laboratories. A laboratory needs to show that the results from an analytical method are reproducible. Reproducibility is similar to repeatability except that the analyses are carried out on identical samples under reproducibility conditions e.g. different operator, different apparatus, different laboratory, long interval of time). Reproducibility limit is similar to repeatability limit except that the results are obtained under reproducibility conditions. 

Whilst the measurement detection and repeatability limits of RDE instruments are in the low parts per million range, the results (for the same sample) provided by a particular manufacturer s instrument will depend on the arc source type and energy, the background correction method, burn time, sample viscosity and the metal particle size distribution in the sample. While individual instruments will generally produce reliable results for used oil analysis, those laboratories requiring multiple instruments should always choose a single manufacturer s type and model. 

Therefore if the difference between duplicated results measured under repeatability conditions is greater than 2.8crr there should be concern that there is something wrong with the analysis. This can be used as part of a quality control procedure to ensure consistency of results. An equivalent difference can be defined for a reproducibility standard deviation (checking results found between laboratories. The maximum permissible difference 2.8 x oy is known as the repeatability limit (r) and 2.8 x [Pg.65]

As a general requirement, the solvents used in spectroscopy should be transparent and stable towards the relevant range of wavelengths. They should be able to dissolve the substance to be examined and not contain impurities affecting the stability of the substance or the validity of the method (selectivity, repeatability, limit of detection, analytical response). Theoretically the solvent chosen should have minimal interaction with the solute. But what could be seen as a disadvantage could also be an important source of structural information. What is called the solvent effect can help in UV, IR and NMR spectroscopies e.g. in struc-... 

Method Repeatability (%) Limit of detection (g) Sample volume (ml) Time (min) Simultaneous analysis... 

Repeatability Limitations. Several studies have documented the low repeatability rate of visual inspection of solder joints. One snch stndy was condncted by AT T at its Federal Systems Division. This study showed that even the same inspector inspecting the same assembly twice had a defect call repeatability rate of only about 50 percent. Two different inspectors inspecting the same assembly had a defect call repeatability rate of only about 28 percent. This study did not include any very-fine-pitch SMT solder joints or 0603 passive components, which are more difficult to inspect visually. 

P Calibration or regression matrix confidence level (repeatability limit... 

Compare the results obtained for mass % aromatics in the original diesel iuel and the two dilutions. These values should agree to within the repeatability limits stated in 13.1.1. If agreement is not obtained, it may be necessary to adjust the restrictor position, FID gas flows, clean the FID, or decrease the iiyection volume. 

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