Meaning
Quality control methodology evaluates a subset of a production lot to determine whether the entire batch meets defined standards. Practical application of statistical acceptance sampling reduces the time and cost of inspection compared to testing every unit. The results provide a level of confidence that the risk of accepting a defective lot remains within pre-defined limits.
Sample Selection
Selection of the units to be tested must be done in a way that represents the entire population of the batch. The sample selection process uses mathematical tables to determine the appropriate number of items to inspect based on the lot size and the desired quality level. Using a random approach prevents the results from being biased by the order in which the parts were produced.
Lot Disposition
Decision to accept or reject the shipment is made immediately after the results of the sample are known. The lot disposition of the goods determines whether they can be moved into inventory or must be returned to the supplier. If the number of defects found in the sample exceeds a certain number, the entire batch is rejected.
This puts the burden of quality back on the manufacturer and protects the buyer from receiving large amounts of faulty material. Clear rules for these decisions prevent arguments between the quality team and the production department.
Probability Factor
Risk of a wrong decision is always present when only a portion of the batch is inspected. The probability factor of the sampling plan defines the chance that a bad lot will be accepted or a good lot will be rejected.
