Sequential Approach to Quality Control Analysis of Inspection Process

Sequential statistical methods have been around since the 1950's but are not widely known or used. We discuss the adaptation of the binomial sequential probability ratio test (SPRT) statistic to a very sensitive problem in quality. The situation was that approximately 750,000 homes and businesses in a major metropolitan area needed to be inspected for mercury contamination as quickly as possible and with a high degree of reliability in the results. Because of the nature of the situation, the quality of the inspection process needed to be demonstrated to meet certain standards as quickly as possible and monitored thereafter.