*Classification of the results by level of agreement
All concentration values are derived from an interlaboratory measurement program. Samples are sent to many laboratories, typically twenty to forty, and the results are analyzed statistically to determine the mean and other statistical parameters.
Certified: The value is calculated from a minimum of 10 sets of data that fulfill specific statistical criteria regarding agreement.
Provisional: The value is calculated from 8 or 9 sets of data that fulfill specific statistical criteria regarding agreement; or alternatively, more than 9 sets of data that do not fulfill the specific statistical criteria required for certification.
Informational: The value is calculated from 7 or fewer sets of data.
Note: Because of different digestion methods used, a single material may show different concentrations for a specific element. Details about methods are provided on the certificate and in the report.
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