The following terms are used here and in literature elsewhere to discuss reference materials.
There are currently 2 names in this directory beginning with the letter B.
How far the measured value lies from the true (or reference) value it is estimating. Bias can also be known as systematic error (an estimate of the level of trueness).
A set of working methods that have been found, through experience and research, to be the best available to use in a particular business or industry. The methods should be described formally and in detail. Mineral assay laboratory competence and documentation is accredited and tested through the National Accreditation Authority (as per ILAC system ISO/IEC 17025). Laboratories in general strive for accreditation for the analytical methods of key commercial importance. For example a laboratory might be 17025 accredited for its iron ore analysis methods but not for platinum analytical methods or may be accredited for Au analysis by Pb collection fire assay with ICP finish at grades between 5 and 10 ppm but not for grades between 0.2 and 1.0 ppm.
Over and above the ISO accreditation system and relevant to mineral laboratories are the Best Practice Laboratory QA/QC systems developed for pathology laboratories through the work of Dr James O. Westgard. “Westgard Rules”. These are multi-rule QC rules that use Control Samples (CRM's) to help analyse whether an analytical run is in-control or out-of-control and should be used by both the laboratory and the customer to monitor that the laboratory’s “Best Practice” procedures are actually working.
Ideally, in the mining and exploration industries, a cost effective "Best Practice" sampling and assay program should at least be recording the following statistics for its internal Quality Management Program:
- The laboratory bias (for the particular method used). This should be very low for samples close to the mine cut-off grade and for very high grade samples. It can be higher for less revenue sensitive analyses, such as for tailings or for geochem programs.
- The relative standard deviation (RSD) or coefficient of variation (CV) for the control sample results. It is important to consider that the single laboratory’s Control Sample RSD should be lower than the RSD from inter-laboratory testing; but the laboratory's Control Limits must still be within the Control Limits derived from the inter-laboratory testing.
- The error detection rate (the critical systematic error). How many of the laboratory errors identified by Control Samples turn out to be real errors upon careful investigation; and not false alarms.
- The false error detection rate. How many of the laboratory errors identified turn out to be false alarms.