Unit 7 & 8 – Acceptance Sampling, Sampling Methods, and Quality Costs

These flashcards cover key points from Units 7 and 8, including acceptance sampling concepts, sampling methods, inspection levels, defect classifications, sampling risks, HACCP principles, and quality cost fundamentals.

What is the primary goal of acceptance sampling compared with control charts?

Acceptance sampling decides whether to accept or reject entire lots after production, whereas control charts monitor the process during manufacture.

In lot acceptance, when is a lot considered acceptable for requirements not based on averages?

When the number of defectives does not exceed the acceptance number (c) of the sampling plan with an AQL of 6.5.

What AQL value is specified for the lot‐acceptance plans discussed in the lecture?

An AQL (Acceptable Quality Limit) of 6.5.

According to the jam standard, when are seeds NOT considered defects?

In berry, dragon fruit, and passion-fruit products, seeds are natural components unless the product is labeled "seedless."

How is a “defective” container defined in Section 3.4?

Any container that fails to meet one or more applicable quality requirements.

Why must samples be selected randomly during acceptance sampling?

To ensure the sample is representative of the entire lot, minimizing bias.

Give two main reasons why 100 % inspection is often impractical.

Lot size may be very large, and some tests are destructive, making full inspection time-consuming and costly.

What information must appear on a Certificate of Sampling?

Who performed the sampling, date/time, product description, sampling location, and reference to the sampling plan used.

When is a sample size of ZERO appropriate?

For destructive tests, very low-risk items, or when strong supplier quality records allow reliance on process control instead of sampling.

List two situations where 100 % sampling is justified.

High-stakes applications (e.g., medical devices, aerospace parts) or very small lot sizes (<100 units) with non-destructive tests.

What is spot-checking and why is it NOT statistically reliable?

An infrequent, non-systematic sampling based on convenience; it lacks randomness and therefore cannot provide valid population inferences.

Describe the constant-percentage sampling policy.

A fixed percentage of every lot is inspected; simple but inefficient for very large or very small populations.

How does the square-root sampling rule determine sample size?

Sample size n = √N, providing smaller samples for large lots compared with a constant percentage.

What three factors are considered when calculating a statistical sample size?

Desired confidence level, margin of error, and population standard deviation.

Define a simple random sample.

Each item and each possible sample have an equal probability of selection.

How is a systematic random sample selected?

Choose a random start within the first k units, then select every k-th unit thereafter (k = N/n).

When is stratified random sampling preferred?

When the population has distinct subgroups (strata) with different characteristics and proportional representation is needed.

Give an example of a cluster in cluster random sampling.

Cases of 24 cans stacked in a warehouse, where each case is treated as a cluster.

Differentiate between variable and attribute data in sampling.

Variables are measured on a continuous scale (e.g., weight); attributes are counted as conforming/non-conforming (e.g., defect present or absent).

What is the difference between a defect and a defective?

A defect is a single non-conformance; a defective is a product containing more defects than allowed (possibly as few as one).

Name the three inspection levels used in sequential sampling plans.

Normal, tightened, and reduced inspection.

What triggers a switch from normal to tightened inspection?

Two consecutive lots are rejected under normal inspection.

After how many acceptable lots can inspection switch from tightened back to normal?

After five consecutive acceptable lots.

Define critical, major, and minor defects.

Critical: certain to cause product failure or safety risk; Major: adversely affects appearance or usability; Minor: negligible effect on performance or shelf life.

What is a sampling plan?

A detailed scheme specifying sample sizes and acceptance/rejection criteria for a lot.

Which sampling plan bases the decision on one sample only?

A single sampling plan.

Why might a double sampling plan be chosen over a single plan?

It allows a second sample if the first is inconclusive, potentially reducing unnecessary lot rejection.

Define producer’s (Type I) risk.

The probability (α) of rejecting a lot that actually meets quality requirements.

Define consumer’s (Type II) risk.

The probability (β) of accepting a lot that does NOT meet quality requirements.

What is an acceptance number (c)?

The maximum number of defects allowed in the sample for the lot to be accepted.

What does LTPD stand for and signify?

Lot Tolerance Proportion Defective; it represents the worst defect level the consumer can tolerate.

How is the rejection number typically related to the acceptance number?

It is usually one more than the acceptance number (c + 1).

Explain the relationship between AQL, producer’s risk, and consumer’s risk.

AQL is the quality level the producer aims to meet; producer’s risk (α) is rejecting good lots (≈5 %), consumer’s risk (β) is accepting bad lots at LTPD (≈10 %).

State the seven HACCP principles in order.

1) Hazard analysis, 2) Identify CCPs, 3) Establish critical limits, 4) Monitor CCPs, 5) Corrective actions, 6) Verification, 7) Record keeping.

What is the formula for Cost of Quality (COQ)?

COQ = Cost of Conformance (prevention + appraisal) + Cost of Non-conformance (internal + external failure).

Give two examples of Cost of Conformance (COC).

Training personnel (prevention) and inspection/testing (appraisal).

Give two examples of Cost of Non-conformance (CONC).

Scrap/rework (internal failure) and warranty returns or recalls (external failure).

Why is minimizing Average Number Inspected (ANI) desirable for the consumer?

Lower ANI reduces inspection cost while still controlling quality.

How can sampling risks be mitigated?

Increase sample size, use proper random techniques (e.g., stratified sampling), and set clear, measurable acceptance criteria.

What is meant by 'switching procedures' in inspection levels?

Rules that dictate movement between normal, tightened, and reduced inspection based on recent lot performance.