ISA CAP Quality Assurance & Improvement 3 — Questions and Answers
Question 1: Which of the following best describes the purpose of a fishbone (Ishikawa) diagram?
- Display data distribution over time
- Identify and organize potential root causes of a problem (Correct answer)
- Rank defects by frequency of occurrence
- Monitor process output against control limits
Correct answer: Identify and organize potential root causes of a problem
A fishbone diagram (cause-and-effect diagram) organizes potential root causes into categories to facilitate structured root cause analysis.
Question 2: In acceptance sampling, what does the Operating Characteristic (OC) curve show?
- The relationship between sample size and inspection cost
- The probability of accepting a lot as a function of its actual defect level (Correct answer)
- The control limits for a process based on sample data
- The cumulative defect rate across production batches
Correct answer: The probability of accepting a lot as a function of its actual defect level
The OC curve plots the probability of lot acceptance against the actual incoming quality level, characterizing the sampling plan's discrimination ability.
Question 3: A process engineer notices the X-bar chart is in control but the R chart shows points above the upper control limit. The most likely cause is:
- The process mean has shifted
- Process variation has increased (Correct answer)
- Measurement equipment needs calibration
- Sample size is too small
Correct answer: Process variation has increased
Points above the UCL on the R chart indicate increased within-subgroup variation, signaling a special cause affecting process spread.
Question 4: What is the Risk Priority Number (RPN) in FMEA calculated as?
- Severity × Occurrence
- Severity × Occurrence × Detection (Correct answer)
- Severity + Occurrence + Detection
- Occurrence × Detection
Correct answer: Severity × Occurrence × Detection
RPN = Severity × Occurrence × Detection, providing a numerical ranking to prioritize which failure modes require the most urgent corrective action.
Question 5: Which sampling method selects every nth unit from a production stream?
- Random sampling
- Stratified sampling
- Systematic sampling (Correct answer)
- Cluster sampling
Correct answer: Systematic sampling
Systematic sampling selects items at fixed intervals (every nth unit) throughout the production run.
Question 6: In a Gage R&R study, if %Gage R&R exceeds 30%, the measurement system is considered:
- Excellent and requires no action
- Marginally acceptable for most applications
- Unacceptable and requires immediate improvement (Correct answer)
- Acceptable only for attribute data
Correct answer: Unacceptable and requires immediate improvement
A %Gage R&R above 30% indicates the measurement system contributes excessive variation and is generally unacceptable for process control or product decisions.
Question 7: Which quality tool is MOST useful for identifying whether two process variables are correlated?
- Control chart
- Pareto chart
- Scatter diagram (Correct answer)
- Check sheet
Correct answer: Scatter diagram
A scatter diagram plots two variables against each other to visually reveal the presence and direction of correlation between them.
ISA CAP Quality Assurance & Improvement 3
Which of the following best describes the purpose of a fishbone (Ishikawa) diagram?