Organization of Proficiency Testing Schemes

Irrespective of the type of proficiency testing scheme, it is usually organized in a sequence of clear steps. 

The scheme organizer lays down the rules for the conduct of the tests and the interpretation of the data. This is circulated to the participants so that they understand exactly how the scheme is run and how their results are assessed. The organizer should establish an expert advisory group which will address issues relating to the operation of the scheme, such as the tests and types of samples to be tested under the scheme, how the performance of participants is to be judged, technical difficulties raised by participants and the performance of participants in the scheme as a whole. 

Materials are chosen such that they are, as far as possible, representative of the type of material that is normally analysed. This will be in terms of the matrix and the concentration range of the analyte. Materials must be tested for homogeneity 

There is no experimentally established optimum frequency for the distribution of samples. The minimum frequency is about four rounds per year. Tests that are less frequent than this are probably ineffective in reinforcing the need for maintaining quality standards or for following up marginally poor performance. A frequency of one round per month for any particular type of analysis is the maximum that is likely to be effective. Postal circulation of samples and results would usually impose a minimum of two weeks for a round to be completed and it is possible that over-frequent rounds have the effect of discouraging some laboratories from conducting their own routine quality control. The cost of proficiency testing schemes in terms of analysts time, cost of materials and interruptions to other work has also to be considered. 

The operation of proficiency testing schemes is described in the harmonized protocol produced by IUPAC [1]. Further information can be found in ISO/IEC Guide 43 [2] and ILAC Guide 13 [3], 

---