Table 10. Acceptable limits.

Recommended practice	CVLT used by the laboratory close to the long term CV of the method: the CVLT will take into account changes in batches, operators, etc. (13).
Acceptable practice	Extended CVLT (30% according to Fisher Snedecor without statistical significant difference) but allowing detection of trends and without exceeding the analytical objective or the maximum CV set by the laboratory for reproducibility during the verification of the method.
Unacceptable practice	The CVLT does not detect trends. Control charts are not derived from laboratory data.
CVLT – long-term coefficient of variation.