Organization, performance, and evaluation of measurements or tests on the same or similar items by two or more laboratories in accordance with predetermined conditions.

Notes:

1. Interlaboratory comparison is a generic term, and the purpose and detailed objectives of an interlaboratory comparison must be specified. Some types of interlaboratory comparisons have special names, for example, proficiency testing scheme and key comparison.
2. Interlaboratory comparisons are organized at all metrological levels and have the following steps in common. a) A coordinator of an interlaboratory comparison plans the interlaboratory comparison; b) One or more items are sourced by the coordinator, assessed as appropriate, and distributed to the participants in an interlaboratory comparison with instructions; c) The participants conduct measurements, tests, examinations, or other work on the item(s) and report the results back to the coordinator; d) The coordinator evaluates the results and provides feedback to the participants; and e) The coordinator and/or the participants act on the results.

Note 3: In some circumstances, one of the laboratories involved in an interlaboratory comparison may be the laboratory that provides the assigned value for the item. The assignment enables the determination of the metrological equivalence of measurement results of the participants but does not, by itself, establish metrological traceability.

3. The minimum number of laboratories participating in an interlaboratory comparison will depend on the metrological properties of the measurement procedures used, for example, measurement precision and analytical selectivity. See, performance characteristics of a measurement procedure.
4. Determination of performance characteristics of a measurement procedure as part of procedure validation or characterization of a candidate reference material can be done by means of an interlaboratory comparison. (See method performance study and material characterization study.)
5. Key comparisons and supplementary comparisons are organized by the International Bureau of Weights and Measures (BIPM) in support of the International Committee for Weights and Measures (CIPM) Mutual Recognition Arrangement (MRA) in which National Metrology Institutes demonstrate the international equivalence of their measurement standards and the calibration certificates and measurement certificates they issue.
6. Accredited laboratories and laboratories seeking accreditation are expected to participate in interlaboratory comparisons, for example, proficiency testing schemes, where available and appropriate.
7. The use of terms such as "ring test", "round robin", "intercalibration", "intercomparison", "collaborative study", etc. for interlaboratory comparisons is not recommended in formal documents.