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338 A · ANALYTICAL CHEMISTRY, VOL. 50, NO. 3, MARCH 1978
m e n t of the d a t a is considered essential in a rigorous evaluation of t h e method for accuracy, precision, sensitivity, and specificity, it is now required for all studies. T h e Association considers this of such importance t h a t it provides statistical assistance in all cases where it is otherwise unavailable to the Associate Referee. A statistical manual (4) is also provided. T h e Associate Referee makes the initial j u d g m e n t on the performance of the method. If he recommends a p proval, it passes to the General Referee and t h e n to a committee of experts. If both recommend approval, the m e t h o d is presented a t t h e Association's a n n u a l business meeting for vote by the membership. Approved m e t h o d s and supporting d a t a are published in t h e Journal of the Association of Official Analytical Chemists. T h e y are subject to scrutiny and general testing by other analysts for a t least a year before final adoption. T h e y may be modified and restudied collaboratively as needed, should feedback from general use reveal flaws in the method or in its written set of directions. Approved m e t h ods are included in the Association's "Official M e t h o d s of Analysis", a book of some 1000 pages which is u p d a t e d every 4 - 5 years. T h e preceding s u m m a r y of AOAC's modus operandi recognizes the need for healthy skepticism toward results obtained by analytical methods which have not undergone such rigorous scrutiny and interlaboratory testing of their accuracy, precision, dependability, specificity, a n d practicality. Selection of Methods for Study A certain degree of variability is associated with all measurements. M u c h of the research on analytical chemistry is an a t t e m p t to minimize t h a t variability. B u t there are many different types of variability in analytical work. We often find t h a t when we a t t e m p t to minimize one kind, we must necessarily permit expansion in another kind. In practical analytical chemistry, the problem often comes down to which variability is to be minimized. Some examples of this point may be helpful. In atomic weight determination, everything—especially practicality—is sacrificed for accuracy. A high degree of accuracy and practicality is required in the assay of precious metals, b u t the fire assay used is generally applicable to little else besides metals and minerals. In clinical chemistry, within -laboratory precision (repeatability) is critical, and often is of greater interest to clinical laboratories t h a n absolute accuracy or agreement with the values of other laboratories (reproducibility). In drug analysis, a high degree of accuracy is required in
