CQIA Statistical Methods 4 — Questions and Answers
Question 1: When constructing a Pareto chart, defect categories are ordered:
- Alphabetically
- By date of occurrence
- From most to least frequent (Correct answer)
- From least to most costly
Correct answer: From most to least frequent
Pareto charts arrange categories from highest to lowest frequency to highlight the vital few contributors.
Question 2: What does a control chart's upper control limit (UCL) represent?
- The maximum customer specification
- Three standard deviations above the process mean (Correct answer)
- The highest recorded data point
- The desired target value
Correct answer: Three standard deviations above the process mean
The UCL is set at ±3 standard deviations from the mean, representing the expected range of common cause variation.
Question 3: A team notices that defect rates differ significantly between the day and night shifts. Which tool would best confirm this finding statistically?
- Scatter diagram
- Histogram comparison or hypothesis test (Correct answer)
- Fishbone diagram
- Affinity diagram
Correct answer: Histogram comparison or hypothesis test
Comparing histograms by shift or running a hypothesis test quantifies whether the difference is statistically significant.
Question 4: Which of the following is an example of attribute data?
- Temperature in degrees Fahrenheit
- Weight of a product in grams
- Pass/fail inspection result (Correct answer)
- Diameter measured with a micrometer
Correct answer: Pass/fail inspection result
Attribute data classifies items into categories (pass/fail, defective/not defective) rather than measuring a continuous scale.
Question 5: The standard deviation of a sampling distribution of means is called the:
- Population standard deviation
- Standard error of the mean (Correct answer)
- Coefficient of variation
- Process sigma
Correct answer: Standard error of the mean
The standard error of the mean equals the population standard deviation divided by the square root of sample size.
Question 6: Which chart is used when subgroup sizes vary and you want to track the proportion of nonconforming items?
- c-chart
- np-chart
- p-chart (Correct answer)
- u-chart
Correct answer: p-chart
The p-chart accommodates variable subgroup sizes by plotting proportion defective rather than count.
Question 7: A box plot (box-and-whisker plot) displays which of the following?
- Only the mean and standard deviation
- The median, quartiles, and potential outliers (Correct answer)
- The frequency of each value
- Correlation between two variables
Correct answer: The median, quartiles, and potential outliers
A box plot shows the median (center line), Q1 and Q3 (box edges), and whiskers extending to min/max or outliers.
CQIA Statistical Methods 4
When constructing a Pareto chart, defect categories are ordered: