ASTM E2554 for Estimating and Monitoring the Uncertainty of Test Results
ASTM E2554 Standard Practice for Estimating and Monitoring the Uncertainty of Test Results of a Test Method in a Single Laboratory Using a Control Sample Program
1. Scope
1.1 This practice describes techniques for a laboratory to estimate the uncertainty of a test result using data from test results on a control sample.
1.2 Uncertainty as defined by this practice applies to the capabilities of a single laboratory. Any estimate of uncertainty determined through the use of this practice applies only to the individual laboratory for which the data are presented.
1.3 The laboratory uses a well defined and established test method in determining a series of test results. The uncertainty estimated using this practice only applies when the same test method is followed. The uncertainty only applies for the material types represented by the control samples, and multiple control samples may be needed, especially if the method has different precision for different sample types or response levels.
1.4 The uncertainty estimate determined by this practice represents the intermediate precision of test results. This estimate seeks to quantify the total variation expected within a single laboratory using a single established test method while incorporating as many known sources of variation as possible.
1.5 This practice does not establish error estimates (error budget) attributed to individual factors that could influence uncertainty.
1.6 This practice describes the use of control charts to evaluate the data obtained and presents a special type of control chart to monitor the estimate of uncertainty.
1.7 The system of units for this Standard is not specified. Dimensional quantities in the Standard are presented only as illustrations of calculation methods. The examples are not binding on products or test methods treated.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D5184 Test Methods for Determination of Aluminum and Silicon in Fuel Oils by Ashing, Fusion, Inductively Coupled Plasma Atomic Emission Spectrometry, and Atomic Absorption Spectrometry
E 177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E 456 Terminology Relating to Quality and Statistics
E 1707 Guide for Estimating Uncertainties in Dosimetry for Radiation Processing
E 2282 Guide for Defining the Test Result of a Test Method
2.2 ASTM Publication:
Manual on Presentation of Data and Control Chart Analysis, 7th Edition
2.3 ISO Standard:
ISO 17025 General Requirements for the Competence of Testing and Calibration Laboratories
3. Terminology
3.1 Definitions - The terminology of Terminology E 456 applies to this practice except as modified herein.
3.1.1 control sample, n - sample taken from a stable, homogeneous material for the purposes of monitoring the performance of a test method in a laboratory.
3.1.1.1 Discussion - The control sample material is representative of the product typically tested in the laboratory by the given test method. A control sample is run periodically using the complete test method protocol to develop a test result. Such test results may be statistically evaluated to monitor test method performance over time. It is not necessary to have an accepted reference value assigned to the control sample material. When the current material is nearly consumed, a replacement material should be run in parallel with the current material to ensure continuity in the control sample program.
3.1.2 check sample, n - see control sample.
3.1.3 uncertainty control chart, n - control chart that includes control limits based on the variation attributed to the uncertainty of the test method.
3.1.4 intermediate precision, n - the closeness of agreement between test results obtained under specified intermediate precision conditions.
3.1.4.1 Discussion - The specific measure and the specific conditions must be specified for each intermediate measure of precision; thus, "standard deviation of test results among operators in a laboratory", or "day-to-day standard deviation within a laboratory for the same operator".
3.1.4.2 Discussion - Because the training of operators, the agreement of different pieces of equipment in the same laboratory and the variation of environmental conditions with longer time intervals all depend on the degree of within-laboratory control, the intermediate measures of precision are likely to vary appreciably from laboratory to laboratory. Thus, intermediate precisions may be more characteristic of individual laboratories than of the test method.
3.1.5 test result, n - the value of a characteristic obtained by carrying out a specified test method.
3.1.6 repeatability, n - precision under repeatability conditions.
