The precision of an analytical procedure expresses the closeness of agreement between the serious of measurements obtained from multiple sampling of the same homogeneous sample under the prescribed conditions. Precision may be considered at three levels: repeatability, intermediate precision and reproducibility. The precision of an analytical procedure is usually expressed as the variance, standard deviation or coefficient of variation of a serious of measurements.
Repeatability (Method Precision)
Repeatability expresses the precision under the operating conditions over a short interval of time. Repeatability is also termed as (Method Precision).Repeatability is usually demonstrated by repeated measurements of a single sample procedure within a laboratory over a short period of time using the same analyst with the same equipment. A minimum six determinations at the test concentration is recommended.
Intermediate precision expresses within-laboratory variations:Different days, different analyst or different equipment, etc. Intermediate precision is usually demonstrated by repeated measurements of the sample used in the repeatability experiment within the same laboratory. Usually the repeatability experiment is repeated on the same sample by a different analyst, on a different day using different equipment if possible.
Reproducibility expresses the precision between laboratories (collaborative studies, usually applied to standardisation of methodology). Reproducibility is usually demonstrated by means of an inter laboratory trial.