Test method

A test method is a definitive procedure that produces a test result. (ASTM definition)

The test result can be qualititive (yes/no), categorical, or quantititive (a measured value). It can be a personal observation or the output of a precision measuring instrument.

Usually the test result is the dependent variable, the measured response based on the particular conditions of the test or the level of the independent variable. Some tests, however, involve changing the independent variable to determine the level at which a certain response occurs: in this case, the test result is the independent variable.

Importance of test methods

In engineering, science, manufacturing, and business, it is vital for all interested people to understand and agree upon methods of obtaining data and making measurements. For example, is common for a physical property to be strongly affected by the precise method of testing or measuring that property. It is vital to fully document experiments and measurements and to provide needed definition to specifications and contracts.

Using a standard test method, perhaps published by a respected standards organization, is a good place to start. Sometimes it is more useful to modify one or to develop a new one. Again, documentation and full disclosure are very necessary.

A well written test method is important. However, even more important is choosing a method of measuring the correct property or characteristic. Not all tests and measurements are equally useful: usually a test result is used to predict or imply sutiability for a certain purpose. For example if a manufactured item has several components, test methods may have several levels of connections:
* test results of a raw material should connect with tests of a component made from that material
* test results of a component should connect with performance testing of a complete item
* results of laboratory performance testing should connect with field performance
* etc

These connections or correlations may be based on published literature, engineering studies, or formal programs such as quality function deployment. Validation of the suitability of the test method is often required.

Content of a test method

The test method might include:

* Descriptive title and scope of the test method
* Date of last effective revision and revision designation
* Person, office, or agency responsible for questions on the test method, updates, and deviations.
* The significance or importance of the test method and its intended use.
* Terminology and definitions to clarify the meanings of the test method
* A listing of the types of apparatus and measuring instrument (sometimes the specific device) required to conduct the test
* Safety precautions
* Required calibrations and metrology systems
* Environmental concerns and considerations
* Sampling procedures. How are samples to be obtained. Number of samples.
* Conditioning: temperature, humidity, etc, and Tolerance (engineering)
* Preparation of samples for the test
* Detailed procedure for conducting the test
* Calculations and analysis of data
* Interpretation of data and test method output
* Report: format, content, data, etc
* Accuracy, precision, systematic bias, repeatability, reproducibility, and uncertainty of test results

See also

*Certified reference materials
*Data analysis
*Design of experiments
*Experiment
*Measurement Systems Analysis
*Measurement uncertainty
*Metrication
*Metrology
*Observational error
*Performance testing
*Replication (statistics)
*Sampling (statistics)
*Specification (technical standard)
*Tolerance (engineering)
*Verification and Validation‎

References

* Pyzdek, T, "Quality Engineering Handbook", 2003, ISBN 0824746147
* Godfrey, A. B., "Juran's Quality Handbook", 1999, ISBN 007034003
* Kimothi, S. K., "The Uncertainty of Measurements: Physical and Chemical Metrology: Impact and Analysis", 2002, ISBN 0873895355
* ASTM D4356 Standard Practice for Establishing Consistent Test Method Tolerances
* ASTM E691 Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
* ASTM E1169 Standard Guide for Conducting Ruggedness Tests
* ASTM E1488 Standard Guide for Statistical Procedures to Use in Developing and Applying Test Methods