closeness of agreement between independent test results obtained under stipulated conditions

proficiency testing
periodic assessment of the performance of individual laboratories and groups of laboratories that is achieved by the distribution by an independent testing body of typical materials for unsupervised analysis by the participants

totality of features and characteristics of a product or service that bear on ist ability to satisfy stated or implied needs

fraction of analyte added to a test sample (fortified or spiked sample) prior to analysis, the unfortified and fortified samples, percentage recovery (%R) is calculated as: %R = [(CF-CU)/CA] x 100

reference material
material or substance the properties of which are sufficiently homogeneous and well established to be used for calibration of an apparatus, assessment of a method or assigning values to materials (e.g. concentration)

certified reference