Loading...
Acceptance sampling is a fundamental quality assurance tool tested on multiple ASQ certification exams, including the Certified Quality Engineer CQE and Certified Quality Auditor CQA. Understanding...
Free practice questions for every ASQ certification.
Create a free account and start practicing in under 60 seconds. No credit card required.
Acceptance sampling is a fundamental quality assurance tool tested on multiple ASQ certification exams, including the Certified Quality Engineer (CQE) and Certified Quality Auditor (CQA). Understanding its principles, application, and related concepts is crucial for passing the exam and excelling in quality management roles.
This guide dives deep into acceptance sampling, key terms like AQL and LTPD, detailed sampling plans, OC curves, and practical examples to help you master the topic.
Acceptance sampling is a statistical quality control technique used to decide whether to accept or reject a lot (batch) of products based on the inspection of a sample from that lot. Instead of inspecting every unit (100% inspection), a smaller subset is tested, saving time and resources.
Acceptance Sampling is preferred when:
100% Inspection is chosen when:
The goal of acceptance sampling is to balance inspection costs with the risk of accepting defective products.
To grasp acceptance sampling, you need to understand the following key terms:
AQL (Acceptable Quality Level):
The maximum percentage (or proportion) of defective items in a lot that is considered acceptable. It represents the quality level the producer aims to meet.
Example: An AQL of 1.5% means up to 15 defective items per 1,000 are acceptable.
LTPD (Lot Tolerance Percent Defective), also called RQL (Rejectable Quality Level):
The worst quality level that the consumer is willing to tolerate. Lots at or worse than this level should have a low probability of acceptance.
Producer's Risk (α):
The risk of rejecting a good lot (meeting the AQL). It is typically set at 5% (α = 0.05).
Consumer's Risk (β):
The risk of accepting a defective lot (exceeding the LTPD). This is usually set at 10% (β = 0.10).
Sampling plans define how many units to inspect and the decision rules for accepting or rejecting a lot. The three main types are:
OC curves display the probability of accepting a lot at various defect levels. They are essential for analyzing the performance of a sampling plan.
Binomial Distribution:
Where:
Poisson Approximation (for large ( n ) and small ( p )):
ANSI/ASQ Z1.4 (Attributes Sampling):
ANSI/ASQ Z1.9 (Variables Sampling):
Switching rules are essential for managing inspection resources while maintaining quality.
Misinterpreting AQL vs. LTPD:
Remember that AQL is the producer's acceptable quality level, while LTPD represents the consumer's tolerance threshold.
Confusing α and β Risks:
OC Curve Misreading:
Be prepared to identify probabilities of acceptance at both AQL and LTPD on OC curves.
Ignoring Switching Rules:
Understand when and how to apply normal, tightened, and reduced inspection.
Scenario:
A supplier delivers 10,000 units of electronic components. Your company has set an AQL of 1.0%. Design a single sampling plan using ANSI/ASQ Z1.4.
Solution Steps:
Decision Rule:
Inspect 125 units. Accept the lot if 2 or fewer defects are found; reject if 3 or more defects are found.
Mastering acceptance sampling and AQL plans is a crucial step toward ASQ certification success. For more detailed guidance, consider enrolling in ASQ Exam Prep Pro at asqexamprep.com, where you'll gain access to expert-led training and resources.
Written by
John Lee
Founder & Lead Instructor, Alpha Training & Consulting
John Lee is the founder of Alpha Training & Consulting, holds 19 ASQ certifications, an MBA in Quality Systems, and a B.S. in Mechanical Engineering. He is a Shingo Prize-winning author and has trained over 2,500 engineers and quality professionals across 25+ years, with students achieving a 93% pass rate on ASQ certification exams.
Create your free ASQ Exam Prep account to access sample questions, BOK domain tracking, and your personalized study dashboard. Upgrade only when you're ready for the full 15,000-question library and John Lee's certification courses.
