Test Method Validation
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Meeting the test method validation requirements of ISO 11607 has often been mistaken as simply using ASTM or other published test methods. Because of the confusion, TIR 22:2007 Annex B was created to give further guidance. Using industry standards often provides the user with a head start on test method validation, but it is not required; in-house test methods may be validated as well.
When using a test method that has been through an interlaboratory study (ILS) with a precision and bias statement, such as some ASTM test methods, most of the initial validation work has been done. Since repeatability and reproducibility evaluations are supplied in the precision statement, what remains is to perform an internal repeatability study to show comparable results to the ILS. This needs to be done using same or similar materials in the ILS. This repeatability study is not intended to replicate values, but replicate similar variability. For integrity tests, the level of sensitivity is also required. If the same level of sensitivity is not required for an application, a rationale must be documented as to why. For further guidance on performing repeatability studies refer to ASTM E 691 Standard Practice for conducting an ILS to determine the precision of a test method.
In-house and other test methods that have not been subject to an ILS have to demonstrate that they are measuring the property intended, that the sensitivity and accuracy are sufficient, and that repeatability can be determined. Validation can be accomplished by consideration and examination of the following:
- Precision. Repeatability (one lab or apparatus) and reproducibility (multiple labs or multiple apparatus) is again required. For further guidance, E691 Conduction an Inter-laboratory Study to Determine Precision of a Test Method.
- Sensitivity. The detection limit of a test method needs to be determined for integrity tests.
For further guidance, refer to ASTM E1488 Standard Guide for Statistical Procedures, E2282 Standard Guide for Defining the Test Results of a Test Method, ASTM E177 Standard terms of the Precision and Bias in ASTM Test Methods, and E456 Standard Terminology Related to Quality and Statistics.
Finally, it is important to recognize that many methods are not tests but are standard means to condition samples for tests. Such methods are performed prior to testing and therefore are not required to be validated. Some conditioning methods that are sometimes mistakenly thought to be test methods are accelerated aging and distribution simulations.