Lecture III: Combination of Assay Results

Some bioassays are undertaken once only for the particular test preparations, perhaps because materials are being screened with a view to selecting for further study those that show some evidence of useful potency or because new batches of a familiar drug must be checked for acceptability of quality. At other times, several assays contribute information on the potency of a particular test preparation relative to a fixed standard. One reason is that physical conditions in a laboratory prevent execution of a single assay large enough for the precision wanted and the experiment is therefore repeated on several occasions. Another reason is that from time to time supplies of a widely agreed reference standard near exhaustion and steps must be taken to replace it by a new standard; a cooperative study involving several groups of people may be undertaken in order to measure the potency of the new standard relative to the old. Publications of the World Health Organization include many reports on such collaborative studies.