4. How do I get a laboratory score?

Interpreting proficiency test data raises at least three questions:

• How to express the value assigned to the material? As this material may eventually be used as an external reference material, it is also important to know how to express the associated uncertainty.

• How to assess the dispersion of test measurements? The results obtained by one laboratory will be judged by comparison with those of other participants.

• How do you judge the suitability of a laboratory? This is a simple practical problem: once the test has been completed, the laboratory must be able to provide a certificate to the auditor in charge of renewing its accreditation.