Newcombe, P.A.; Allen, O.B. (1988, ASQC and the American Statistical Association) The Reader's Digest Association (Canada) Ltd., Canada; University of Guelph, Canada
A three-class procedure for acceptance sampling by variables is introduced as an alternative to both the three-class attributes plans introduced by Bray, Lyon, and Burr (1973) and the two-class variables plans introduced by Jennett and Welch (1939). The procedure, which requires that the quality characteristic be normally distributed, has the advantage of requiring a smaller sample size than a three-class attributes plan with approximately the same operating characteristic (OC) surface. The advantage of the three-class variables plan over the two-class variables plan is an ability to discriminate between lots with high and low percentages of marginally conforming items. Two equivalent methods of stating the decision rules for the plans are suggested. It is shown that the OC surface for the three-class variables procedure may be constructed with a special case of the bivariate noncentral t distribution. Motivation and methods for choosing a plan are discussed and illustrated.
Attributes sampling plans,Statistics,Variation