CQIA Statistical Methods 2 — Questions and Answers
Question 1: A process has a mean of 50 and a standard deviation of 5. What percentage of data falls within one standard deviation of the mean (45 to 55) in a normal distribution?
- 68% (Correct answer)
- 95%
- 99.7%
- 50%
Correct answer: 68%
In a normal distribution, approximately 68% of data falls within ±1 standard deviation of the mean.
Question 2: Which type of data can be ranked but does not have equal intervals between values?
- Ratio data
- Interval data
- Ordinal data (Correct answer)
- Nominal data
Correct answer: Ordinal data
Ordinal data can be ranked in order, but the differences between ranks are not necessarily equal.
Question 3: A run chart shows 8 consecutive data points above the centerline. This is an indicator of:
- Normal variation
- A special cause (Correct answer)
- An acceptable process
- Random noise
Correct answer: A special cause
Eight or more consecutive points on one side of the centerline signal a non-random pattern indicating a special cause.
Question 4: What does a p-chart monitor in statistical process control?
- Average measurement values
- Proportion of defective units (Correct answer)
- Number of defects per unit
- Process variability
Correct answer: Proportion of defective units
A p-chart tracks the proportion (fraction) of nonconforming (defective) units in a sample.
Question 5: Which measure of central tendency is most affected by extreme outliers?
- Median
- Mode
- Mean (Correct answer)
- Range
Correct answer: Mean
The mean is calculated using all values, so extreme outliers pull it significantly toward them.
Question 6: A scatter diagram shows data points forming a tight cluster sloping downward from left to right. This indicates:
- Strong positive correlation
- No correlation
- Strong negative correlation (Correct answer)
- Weak positive correlation
Correct answer: Strong negative correlation
A downward sloping tight cluster indicates a strong negative correlation between the two variables.
Question 7: In a histogram, what does it mean when the distribution is skewed to the right?
- The tail extends to the left
- Most values are above the mean
- The tail extends to the right with a few high values (Correct answer)
- The data is normally distributed
Correct answer: The tail extends to the right with a few high values
Right skew means the tail is on the right side, indicating a few unusually high values pulling the distribution.
CQIA Statistical Methods 2
A process has a mean of 50 and a standard deviation of 5.
What percentage of data falls within one standard deviation of the mean (45 to 55) in a normal distribution?