requiring less than 100% inspection can provide 100% assurance that no nonconforming items will pass the inspection process. The definitions of nonconformance and appropriate quality/safety goals involve careful balancing of the costs and utility of two types of errors:
A type I error occurs if a lot that is satisfactory is erroneously rejected, causing an economic loss to the supplier.
A type II error occurs if a lot that is unsatisfactory is erroneously accepted, causing economic and safety risks for both the supplier and the consumer.
As indicated by this phrasing, the two types of errors are not of equivalent value. A decision on their relative values and its consequences for sampling involve serious questions of social policy. The failure to develop formal sampling plans based on these risks may, in some cases, result from the reluctance to face these questions explicitly.
Two types of sampling procedures, which are named for their application, are currently used by the FDA in its inspection of fishery products: surveillance samples and compliance samples. The purpose of surveillance samples is to ascertain the overall characteristics of seafood, whereas the purpose of compliance samples is to determine whether a suspected lot meets regulatory requirements.
For either type of sample, there is a danger that many contaminated fish will pass unnoticed because most lots are not inspected at all, and for those that are, the sample is extremely small. Large samples are not practical because of the destructive nature of most testing.
In many tests, the samples must be sent to a laboratory for evaluation. In these cases, unless the product is frozen, the lot may be consumed before the results are obtained. Thus, a possible health hazard may be discovered only in time to prevent the distribution of future lots from the same source.
If sufficient control could be maintained on the suppliers of seafood, there would be little need to inspect their products. Such control is not feasible, however, because of the diversity of producers and raw products. In spite of this, the committee recommends that the responsible agency develop a procedure that will enable it to gain enough confidence in certain suppliers for inspection of their products to be virtually eliminated, or at least made with reduced frequency. This would enable compliance inspection to concentrate on a smaller population of seafood producers. Some efforts are currently underway to develop such a procedure.
For surveillance inspection, which is performed to obtain an estimate of the overall safety of fishery products, samples of incoming lots must first be made. To be representative, these samples should be random. A stratified random sampling procedure is recommended to select lots for sampling. Stratification would be based on harvesting areas and would ensure that lots selected are representative. Once the lots have been selected, random samples of fish should be chosen from each lot for inspection. Details of this procedure may be found in Cochran (1977) or Eberhardt (1990).