SPC Data Collection & Interpretation 3 — Questions and Answers
Question 1: A process produces shaft diameters measured to 0.001 inch. This is an example of:
- Variable (continuous) data (Correct answer)
- Attribute data
- Go/no-go data
- Binomial data
Correct answer: Variable (continuous) data
Measurements on a continuous scale such as diameter are variable data, allowing infinite values within a range.
Question 2: When a gage is used to collect SPC data, gage R&R studies are conducted to assess:
- Measurement system repeatability and reproducibility (Correct answer)
- Process capability only
- The number of defects produced
- Sample size adequacy
Correct answer: Measurement system repeatability and reproducibility
Gage R&R quantifies how much of the observed variation comes from the measurement system itself (repeatability) versus different operators (reproducibility).
Question 3: In a histogram of process data, a bimodal shape most likely indicates:
- Two distinct process streams or populations are mixed in the data (Correct answer)
- The process is perfectly centered
- Only common cause variation is present
- The sample size is too small
Correct answer: Two distinct process streams or populations are mixed in the data
Two peaks in a histogram suggest that data from two different populations or process conditions have been combined.
Question 4: An operator collects 5 measurements every hour for 20 hours. The subgroup size (n) and number of subgroups (k) are:
- n = 5, k = 20 (Correct answer)
- n = 20, k = 5
- n = 100, k = 1
- n = 1, k = 100
Correct answer: n = 5, k = 20
Each hourly sample of 5 measurements is one subgroup, so n = 5 measurements per subgroup and k = 20 subgroups total.
Question 5: Which data collection error occurs when an inspector unconsciously rounds measurements toward a preferred value?
- Bias or systematic error (Correct answer)
- Random measurement error
- Sampling error
- Transcription error
Correct answer: Bias or systematic error
Consistently rounding toward a value introduces a systematic bias that shifts all measurements in one direction.
Question 6: A Pareto chart is used during data interpretation to:
- Identify the vital few defect categories that account for most problems (Correct answer)
- Plot process data over time to detect trends
- Compare the mean and standard deviation of subgroups
- Show the distribution shape of continuous measurements
Correct answer: Identify the vital few defect categories that account for most problems
A Pareto chart ranks defect categories by frequency to apply the 80/20 rule and focus improvement efforts on the most significant issues.
Question 7: Data collected in the order of production is called:
- Time-ordered or sequential data (Correct answer)
- Stratified data
- Attribute data
- Clustered data
Correct answer: Time-ordered or sequential data
Time-ordered data preserves the sequence of production, which is essential for detecting trends and special causes on control charts.
SPC Data Collection & Interpretation 3
A process produces shaft diameters measured to 0.001 inch.
This is an example of: