3
(i.e., ‘PTM’ vs. ‘Official’ designation), have led to a great reduction in validation studies which
involve collaborative studies.
As of 2012, a new ‘alternative’ methodology to ‘official first action’ has been implemented at
AOAC. This new policy allows an ‘official’ status to new methods based on presented single
laboratory evidence plus other anecdotal data. The method would be transitioned to ‘final action’
after a period of a year or more in which reproducibility, recovery and repeatability information
is collected. The type of evidence which will be considered acceptable for final action has not yet
been defined.
Proficiency testing (‘PT’) is an economical approach to a multicollaborator study which has the
specific principal goal of measuring a participating collaborator result with respect to the mass of
the other collaborator results. PT studies are generally performed for a nominal (middle)
concentration of analyte in a particular matrix. Participants may use nominally the same method,
but typically there is no direct control over the exact protocol used. Replication may or may not
be present, and may vary among participants, sometimes without disclosure.
The use of PT data has been proposed as a possible surrogate for the traditional collaborative
study. PT experiments require less intensive involvement for collaborators, so recruitment is
easier, and involve typically a single concentration of a single matrix, so deployment is easier.
The difficulty is the lack of control and design in PT studies that results in lack of repeatability
conditions and lack of interpretability of the reported results. Table 1 shows a comparison of the
properties of a collaborative vs. a PT study:
Recommended to OMB by Committee on Statistics: 07-17-2013
Reviewed and approved by OMB: 07-18-2013
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