1. The Certified Quality Process Handbook Chapter 18: Sampling
Presented by Dr. Joan Burtner
Certified Quality Engineer
Associate Professor and Chair
Dept. of Industrial Engineering and Industrial Management
Mercer University

2. Introduction to Acceptance Sampling
Acceptance Sampling Definition: the process of inspecting a portion of the product in a lot for the purpose of making a decision regarding classification of the entire lot as either conforming or nonconforming to quality specifications.
Acceptance Sampling Advantages
Lower inspection costs because fewer units are inspected
Less time required (when compared to 100% inspection)
Less risk of damage to the product due to reduced handling
Increased emphasis on the supplier’s responsibility for quality
IDM355 Fall 2015
Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering

3. Acceptance Sampling by Attributes
Purpose
Protection from accepting lots from a continuing process whose average quality deteriorates beyond an acceptable quality level
Protection against isolated lots that may have levels of nonconformances greater than can be considered acceptable
ANSI/ASQ Z is the most widely used standard
Acceptable Quality Level (AQL) – the maximum percent or fraction of nonconforming units in a lot or batch that, for the purposes of acceptance sampling, can be considered satisfactory as a process average
Lot Tolerance Percent Defective (LTPD) – the poorest quality in an individual lot that should be accepted
IDM355 Fall 2015
Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering

4. Producer’s and Consumer’s Risks
Producer’s risk (alpha)
The probability of rejecting a lot that is within the acceptable quality level
The producer faces a possibility of having a lot rejected even though the lot has met the requirements set by the AQL
Consumer’s risk (beta)
The probability of acceptance for a designated numerical value of relatively poor submitted quality
The probability of accepting a lot that has a quality level equal to the LTPD
IDM355 Fall 2015
Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering

5. Single Sampling Plan Parameters
A single sampling plan is described by the lot size, the sample size (n), and the acceptance number(c).
Operating characteristic (OC) curves
Graphical representation of the relationship of the probability of accepting a lot vs. the percent nonconforming
Figure 18.3 – acceptance number c is held constant
Figure 18.4 – sample size n is held constant
IDM355 Fall 2015
Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering

6. Types of Sampling Plans
Single
The decision to accept or reject the lot is based on the results of the inspection of a single sample
Reject the lot if the number of defective items in the sample is greater than the acceptance number (c)
Double
Take a sample of size n1. If the number of defective items is less than or equal to c1, accept the lot. If the number of defective items in the sample is greater than r1, reject the lot. Otherwise, take a second sample of size n2.
If the number of combined defectives is less than or equal to c2, accept the lot. Otherwise reject the lot.
Multiple (extension of double sampling for up to seven samples)
IDM355 Fall 2015
Dr. Joan Burtner, Assoc. Prof. and Chair, Dept. of Industrial Engineering