Anything you do in a forensic laboratory, there will be proficiency tests for it.
Laboratories undergo periodic proficiency testing to ensure that techniques remain reliable in analysts’ hands.
The proficiency testing regimen is a two-step process. The actual testing and identifying of errors is only the initial stage. In the follow-up phase, the laboratory attempts to identify the root causes of errors, and take corrective action. Proficiency testing alerts a lab to systemic issues (in protocol, environment, training, etc.) that can be explored and corrected.
Through a complex series of decisions, proficiency tests are designed, constructed, and finally implemented to evaluate and improve the reliability of results. If a test is designed to identify a compound, substance, or drug, how much of the substance should be used in the test? It may be straightforward to identify a specimen containing a milligram of the material, but much more difficult if it contains only a microgram. What’s the objective of each test? What and whom will be tested?
How often does a particular analyst make an error? This is determined or estimated, if it can be, by proficiency testing. But it’s not a perfect system. For example, it’s virtually impossible to establish a meaningful error rate for a DNA analyst, because relatively few proficiency tests are done in a year, due to the time needed to complete them.