To statistical approach are most common: acceptance sampling and statistical process control.
Acceptance sampling is a statistical technique that involves evaluating random samples from a group, or "lot," of produced materials to determine whether the lot meets acceptable quality levels.
An acceptable quality level (AQL) is a predetermined standard against which the random samples are compared. If a certain number of the samples fall below the AQL, the entire lot will be rejected. It normally represents feedback control.
Statistical process control is a statistical technique the uses periodic random samples taken during production to determine whether acceptable quality levels are being met or production should be stopped for remedial action.
In contrast to acceptance sampling, statistical process control assesses quality during actual production so that problems can be resolved before materials are completed.