Your Study Guide to ASTM D6299 Terminology
When it comes to ASTM D6299, it's important that we speak the same language. ASTM D6299 is a critical piece of the EPA Tier 3 qualification process.
Anyone who has read this 25+ page method knows it can be a tough go if you are not in the mood to immerse yourself in the world of statistical quality control (SQC). Raise your hand if you can remember the last time you were in this mood. Seeing none, I would like to present the key terms you need to know when discussing SQC. Hand-crafted by the members of the ASTM subcommittee D02.94 on Quality Assurance and Statistics, this short glossary is sure to increase your knowledge regarding SQC. Study up!
Accepted reference value:
A value that serves as an agreed-upon reference for comparison and that is derived as
- A theoretical or established value, based on scientific principles,
- An assigned value, based on experimental work of some national or international organization, such as the U.S. National Institute of Standards and Technology (NIST),
OR - A consensus value, based on collaborative experimental work under the auspices of a scientific or engineering group.
Accuracy
The closeness of agreement between an observed value and an accepted reference value.
Assignable cause
A factor that contributes to variation and that is feasible to detect and identify.
Bias
A systematic error that contributes to the difference between a population mean of the measurements or test results and an accepted reference or true value.
Control limits
Limits on a control chart that are used as criteria for signaling the need for action or for judging whether a set of data does or does not indicate a state of statistical control.
Lot
A definite quantity of a product or material accumulated under conditions that are considered uniform for sampling purposes.
Precision
The closeness of agreement between test results obtained under prescribed conditions.
Repeatability conditions
Conditions where mutually independent test results are obtained with the same test method in the same laboratory by the same operator with the same equipment within short intervals of time, using test specimens taken at random from a single sample of material.
Reproducibility conditions
Conditions under which test results are obtained in different laboratories with the same test method, using test specimens taken at random from the same sample of material.
The terms below are specific to ASTM D6299-13*.
*D6299-13 is specifically called out in the EPA Tier 3 regulation. Unless the EPA decides to change this in the future be sure to reference this version of D6299 when aiming to comply with Tier 3. Check out our post discussing EPA Tier 3 or ASTM D6299 for more information.
Analytical measurement system
A collection of one or more components or subsystems, such as samplers, test equipment, instrumentation, display devices, data handlers, printouts or output transmitters, that is used to determine a quantitative value of a specific property for an unknown sample in accordance with a test method.
- Note: A standard test method (for example, ASTM, ISO) is an example of an analytical measurement system.
- Note: An analytical measurement system may comprise multiple instruments being used for the same test method provided there is no statistically observable bias and precision differences between the multiple instruments
Blind submission
Submission of a check standard or quality control (QC) sample for analysis without revealing the expected value to the person performing the analysis.
In QC testing, a material having an accepted reference value used to determine the accuracy of a measurement system.
- Note: A check standard is preferably a material that is either a certified reference material with traceability to a nationally recognized body or a material that has an accepted reference value established through interlaboratory testing.
- Note: For some measurement systems, a pure, single component material having known value or a simple gravimetric or volumetric mixture of pure components having calculable value may serve as a check standard.
- Note: Users should be aware that for measurement systems that show matrix dependencies, accuracy determined from pure compounds or simple mixtures may not be representative of that achieved on actual samples.
Common (chance, random) cause
For quality assurance programs, one of generally numerous factors, individually of relatively small importance, that contributes to variation, and that is not feasible to detect and identify.
Double blind submission
Submission of a check standard or QC sample for analysis without revealing the check standard or QC sample status and expected value to the person performing the analysis.
In-statistical-control
A process, analytical measurement system, or function that exhibits variations that can only be attributable to common cause.
Proficiency testing
Determination of a laboratory’s testing capability by participation in an interlaboratory crosscheck program.
- Note: ASTM Committee D02 conducts proficiency testing among hundreds of laboratories, using a wide variety of petroleum products and lubricants.
For use in quality assurance programs to determine and monitor the precision and stability of a measurement system, a stable and homogeneous material having physical or chemical properties, or both, like those of typical samples tested by the analytical measurement system. The material is properly stored to ensure sample integrity, and is available in sufficient quantity for repeated, long term testing
Site expected value (SEV)
For a QC sample this is an estimate of the theoretical limiting value towards which the average of results collected from a single in-statistical control measurement system under site precision conditions tends as the number of results approaches infinity.
- Note: The SEV is associated with a single measurement system; for control charts that are plotted in actual measured units, the SEV is required, since it is used as a reference value from which upper and lower control limits for the control chart specific to a batch of QC material are constructed.
Site precision
The value below which the absolute difference between two individual test results obtained under site precision conditions may be expected to occur with a probability of approximately 0.95 (95 %). It is defined as 2.77 times the standard deviation of results obtained under site precision conditions.
Site precision conditions
Conditions under which test results are obtained by one or more operators in a single site location practicing the same test method on a single measurement system which may comprise multiple instruments, using test specimens taken at random from the same sample of material, over an extended period of time spanning at least a 15-day interval.
- Note: Site precision conditions should include all sources of variation that are typically encountered during normal, long term operation of the measurement system. Thus, all operators who are involved in the routine use of the measurement system should contribute results to the site precision determination.
- Note: If multiple results are obtained within a 24 hour period, then it is recommended that the number of results used in site precision calculations be increased to capture the longer-term variation in the system.
Site precision standard deviation
The standard deviation of results obtained under site precision conditions.
Validation audit sample
A QC sample or check standard used to verify precision and bias estimated from routine quality assurance testing.
POP QUIZ!
Just kidding, but knowing these terms and definitions will keep us all speaking the same language. The language of quality!
