ASTM D3321 Standard Test Method for Use of the Refractometer for Field Test Determination of the Freezing Point of Aqueous Engine Coolants
9. Precision and Bias
9.1 The precision of this test method is based on an interlaboratory study conducted in 2011. Twelve laboratories tested four different materials for two different properties. Each "test result" represents an individual determination. Each laboratory reported triplicate test results for each analysis. Practice E691 was followed for the design and analysis of the data; the details are given in RR:D15-1032.
9.1.1 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.
9.1.1.1 Repeatability limits are listed in Tables 1 and 2.
9.1.2 Reproducibility Limit, 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 equipment in different laboratories.
9.1.2.1 Reproducibility limits are listed in Tables 1 and 2.
9.1.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.
9.1.4 Any judgment in accordance with statements 9.1.1 and 9.1.2 would have an approximate 95% probability of being correct.
9.2 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.
9.3 The precision statement was determined through statistical examination of 288 results, from twelve laboratories, on four different materials.
10. Keywords
10.1 engine coolants; freezing point; refractometer
