Evaluation of analytical methods within a context of use

There is no such thing as a ''good method'' or a ''bad method'' because methods must be evaluated for a particular purpose. A method which is ideal for one purpose may be totally inadequate for another. Thus, to ask if a method is good is to ask only half of a question; one must ask if it is good for a particular purpose. Methods must be evaluated within a context of use. Good methods frequently evolve in a context of use, and are developed for a particular purpose. The USDA STOP TEST was designed for the rapid determination of antibiotics in meat. A sterile cotton swab is exposed to tissue fluids and placed on a petri plate seeded with bacteria sensitive to several antibiotics. If the animal fluids contain antibiotics, a zone of inhibition is seen around the cotton swab. The test is based on well-known principles, and is simple, inexpensive, portable, and sensitive. As a screening test it is excellent, but as a confirmatory test legal action it would be totally unsuitable, because the cause of the inhibition is not identified; it could be from an antibiotic residue or from an elevated serum component of the animal. The suitability of the test must rest on the context of its use.