ASTM D2809 Standard Test Method for Cavitation Corrosion and Erosion-Corrosion Characteristics of Aluminum Pumps With Engine Coolants
10. Precision and Bias
10.1 The precision of this test method is based on interlaboratory study of Test Method D2809, conducted in 2008. Each of four laboratories tested two coolants. Every "test result" represents an individual determination. Each laboratory was asked to report duplicate rating results. Except for the limited variety of materials tested, and the availability of replicate data from only four laboratories, Practice E691 was followed for the design and analysis of the data; the details are given in a research report.
10.1.1 Repeatability Limit (r) - Two test results obtained within one laboratory shall be judged not equivalent if they differ by more than the "r" value for that material; "r" is the interval representing the critical difference between two test results for the same material, obtained by the same operator using the same equipment on the same day in the same laboratory.
10.1.1.1 Repeatability limits are listed in Table 2.
10.1.2 Reproducibility Limt (R) - Two test results shall be judged not equivalent if they differ by more than the "R" value for that material; "R" is the interval representing the critical difference between two test results for the same material, obtained by different operators using different equipemtn in different laboratories.
10.1.2.1 Reproducibility limits are listed in Table 2.
10.1.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.
10.1.4 Any judgment in accordance with 10.1.1 and 10.1.2 would normally have an approximate 95 % probability of being correct, however the precision statistics obtained in the ILS must not be treated as exact mathematical quantities which are applicable to all circumstances and uses. The limited number of reporting laboratories, and materials tested, guarantees that there will be times when differences greater than predicted by the ILS results will arise, sometimes with considerably greater or smaller frequency than the 95 % probability limit would imply. Consider the repeatabilty limit and the reproducibilty limit as general guides, and the associated probability of 95 % as only a rough indicator of what can be expected.
10.2 Bias - At the time of the study, there was no accepted reference material suitable for determining the bias for this test method, therefore no statement on bias is being made.
10.3 The precision statement was determined through statistical examination of 16 results, from four laboratories, on the two coolants described below:
Sample 1 Pink
Sample 2 Green
11. Keywords
11.1 aluminum; automotive; cavitation corrosion; engine coolant; erosion-corrosion; pumps; test
