You may find this glossary useful in relation to proficiency testing in general, as well as that of Fapas® proficiency tests.
Accuracy
The closeness of agreement between a test result and the accepted reference value. NOTE. The term "accuracy", when applied to a set of test results, describes a combination of random components and a common systematic error or bias component.
Assigned value
The value to be used as the "true" value by Fapas® PT in the statistical treatment of results. It is the best available estimate of the true value of the analyte in the matrix.
Bias
The difference between the expectation of the test results and an accepted reference value.
NOTE. Bias is due to systematic error, not random error. There may be one or more systematic error components contributing to the bias. A larger systematic difference from the accepted reference value is reflected by a larger bias value.
Bias of the measurement method
The difference between the expectation of test results obtained from all laboratories using that method and an accepted reference value. NOTE. An example of this is where a method purporting to measure the sulfur content of a compound consistently fails to extract all the sulfur, giving a negative bias to the measurement method. The bias of the measurement method is measured by the displacement of the average of results from a large number of different laboratories all using the same method. The bias of a measurement method may be different at different analyte concentrations.
Certified Reference Material (CRM)
A reference material, one or more of whose property values are certified by a technically valid procedure, accompanied by or traceable to a certificate or other documentation which is issued by a certifying body.
Consensus value
The assigned value, as generated from valid participants' results. some participants' results may be excluded from the consensus calculation where they fail to meet specific criteria. The consensus value may be the robust mean, median or mode.
Distribution unit
One sample of the test material which is sent to a participant.
Error
The difference between a reported result and the assigned value.
Fapas®
Brand name owned by Fera Science Ltd providing the Fapas® Food Chemistry, Fapas® Food Microbiology, Fapas® GM, Fapas® Water and Environmental and specialised proficiency testing schemes.
Fera
Fera Science Ltd, parent organisation of Fapas®
Fitness for Purpose
Toe precision and accuracy of analytical data must be sufficient to enable the end-user of the data to make sound decisions as to whether the results/samples analysed are fit for the intended purpose.
Interlaboratory test comparisons
Organisation, performance and evaluation of tests on the same or similar items or materials by two or more different laboratories in accordance with pre-determined conditions.
Internal Quality Control (IQC)
The set of procedures undertaken by the laboratory staff for continuous monitoring of operations and results in order to decide whether the results are reliable enough to be released; IQC primarily monitors the batch-wise trueness of results on quality control materials, and precision on replicate analysis of test materials.
Laboratory bias
Toe difference between the expectation of the test results from a particular laboratory and an accepted reference value.
Laboratory component of bias
The difference between the laboratory bias and the bias of the measurement method. NOTES. (1) The laboratory component of bias is specific to a given laboratory and the conditions of measurement within the laboratory, and it may be different at different analyte concentrations. (2) The laboratory component of bias is relative to the overall average result, not the true or reference value.
LLI
Lower Limit of Interest
Precision
The closeness of agreement between independent test results obtained under prescribed conditions. NOTES. (1) Precision depends only on the distribution of random errors and does not relate to the accepted reference value. (2) The measure of precision is usually expressed in terms of imprecision and computed as a standard deviation of the test results. Higher imprecision is reflected by a larger standard deviation. (3) "Independent test results" are defined as results obtained in a manner not influenced by any previous result for the same or similar material.
Proficiency Testing Scheme (Performance Assessment Scheme)
The system for objectively checking laboratory results by means of an external agency (e.g. Fapas®®). It includes comparison of a laboratory's results at Intervals with those of other laboratories, the main object being the establishment of trueness. Proficiency testing is designed to assess the accuracy of a laboratory's results. Proficiency testing is sometimes referred to as "external quality assessment" (EQA).
QC materials
Surplus test materials from the batch used for a PT. Useful for internal quality control (QC) in a laboratory but these are not CRMs.
Quality Assurance System/Programme (QAS)
The sum total of a laboratory's activities aimed at achieving the required standard of analysis. While IQC and proficiency testing are very important components of a quality assurance programme it must also Include staff training, administrative procedures, management structure, auditing, etc. Accreditation bodies judge laboratories on the basis of their quality assurance programme plus peer review of technical competence for a specific technical capability.
Reference Material (RM)
A material or substance one or more properties of which are sufficiently homogeneous and well established to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to other materials.
Relative Standard Deviation (RSDD) / (Coefficient of Variance)
The standard deviation expressed as a percentage of the mean:
RSD= σ/χ‾ ×100
where σ is the standard deviation and χ‾ is the arithmetic mean
Robust mean
The mean of results calculated by a robust statistical method, for example Huber's HlS algorithm as used by Fapas®®.
Standard deviation for proficiency (target sd)
A numerical value for the standard deviation of a measurement result, which has been designated as a goal for measurement quality.
Test material
The matrix/analyte combination to be tested that Is distributed to participants In the proficiency test.
Test method
A defined technical procedure to determine one or more specified characteristics of a material or product.
Testing laboratory
A laboratory that measures, examines, tests, calibrates or otherwise determines the characteristics or performance of materials or products.
True value
The actual concentration of the analyte in the matrix. Very often, the true value is unknown.
Trueness
The closeness of agreement between the average value obtained from a large series of test results and an accepted reference value. NOTE. The measure of trueness is usually expressed in terms of bias.