SEQUENTIAL DEFECT REMOVAL SAMPLING

Standard inspection methods underestimate the true number of defects o r nonconformities in a complex product (e.g., automobile, mobile home, airplane, circuit board, computer program) when an inspector is unabl e to identify every defect with certainty. A nonlinear statistical mod el with a nonlinear constraint is developed for estimating the unknown number of defects in a product when inspection is imperfect. A sequen tial defect removal sampling plan is defined in which two or more insp ectors examine in sequence a product or sample of products and then ma rk or correct any observed defects prior to the next inspection. The n umber of defects identified by each inspector provides the information needed to estimate the number of defects in the product in addition t o the number of defects that have eluded all inspectors. A goodness-of -fit test of model assumptions is presented. A test of hypothesis rega rding the unknown number of defects in quality improvement experiments also is described.