Quality Auditor Certification Statistical Sampling 3 — Questions and Answers
Question 1: In ANSI/ASQ Z1.4, what happens to the sampling plan when a lot is submitted under tightened inspection and a second lot is rejected?
- Inspection reverts immediately to normal
- Production is halted until the issue is corrected
- The sampling plan switches to reduced inspection
- Acceptance of product is discontinued until corrective action is taken (Correct answer)
Correct answer: Acceptance of product is discontinued until corrective action is taken
Under Z1.4, if five consecutive lots are rejected on tightened inspection, acceptance of the product must be discontinued.
Question 2: A quality engineer applies a hypergeometric distribution rather than a binomial distribution when sampling. This choice is most appropriate when:
- The population is very large relative to the sample
- The sample is a significant fraction of a finite population (Correct answer)
- The defect rate exceeds 10%
- The sample size exceeds 30 units
Correct answer: The sample is a significant fraction of a finite population
The hypergeometric distribution applies when sampling without replacement from a finite population where the sample is a substantial fraction.
Question 3: Average Total Inspection (ATI) in acceptance sampling includes which components?
- Only the sample items inspected
- Sample items plus all items in rejected lots that are 100% inspected (Correct answer)
- All items in every submitted lot regardless of acceptance
- Only the items found defective during sampling
Correct answer: Sample items plus all items in rejected lots that are 100% inspected
ATI accounts for sample inspection plus the full 100% inspection of all rejected lots after they are screened.
Question 4: Which of the following best describes the Lot Tolerance Percent Defective (LTPD)?
- The maximum allowable defect rate the consumer will accept with high confidence
- The defect rate at which there is a 10% probability of acceptance (consumer's risk point) (Correct answer)
- The AQL multiplied by the tightening factor
- The average defect rate across all submitted lots
Correct answer: The defect rate at which there is a 10% probability of acceptance (consumer's risk point)
LTPD is the defect level at which the probability of lot acceptance equals the consumer's risk (typically 10%).
Question 5: A double sampling plan with n1=50, c1=1, r1=4, n2=100, c2=3 means a lot is accepted outright if the first sample yields:
- Exactly 0 defectives
- 1 or fewer defectives (Correct answer)
- 3 or fewer defectives
- Between 2 and 4 defectives
Correct answer: 1 or fewer defectives
In a double sampling plan, the lot is accepted after the first sample if defectives found are ≤ c1 (1 in this case).
Question 6: When using variables sampling plans (such as ANSI/ASQ Z1.9), what assumption about the data is required?
- Data must follow a uniform distribution
- Measurements must come from a normally distributed population (Correct answer)
- At least two defect types must be measured
- The sample size must be larger than attribute plans
Correct answer: Measurements must come from a normally distributed population
Variables sampling plans assume normality because they use the mean and standard deviation to estimate the fraction defective.
Question 7: Rectifying inspection refers to a sampling procedure where:
- All units are inspected before any are shipped
- Defectives found in samples and rejected lots are replaced with conforming units (Correct answer)
- Only the first lot from a new supplier is fully inspected
- Sampling plans are adjusted in real time based on defect counts
Correct answer: Defectives found in samples and rejected lots are replaced with conforming units
Rectifying inspection replaces detected defectives, so the outgoing quality is always better than the incoming lot quality.
Quality Auditor Certification Statistical Sampling 3
In ANSI/ASQ Z1.4, what happens to the sampling plan when a lot is submitted under tightened inspection and a second lot is rejected?