Statistical Process Control (SPC) MCQs With Answer

Statistical Process Control (SPC) MCQs With Answer is a focused quiz resource tailored for M.Pharm students studying Quality Management Systems. This collection emphasizes practical understanding of SPC concepts used in pharmaceutical manufacturing — control charts, process capability, sampling strategies, and interpretation of signals indicating common or special causes of variation. Each question explores real-world applications such as rational subgrouping, selection of appropriate chart types for attributes and variables, handling non-normal data, and modern techniques like EWMA and CUSUM. Answers are provided for self-assessment. Use these MCQs to strengthen analytical skills required for maintaining consistent product quality, regulatory compliance, and effective process improvement in pharmaceutical operations.

Q1. Which control chart is most appropriate for monitoring the mean potency of a drug batch measured continuously in subgroups of size 5?

• X-bar chart
• p-chart
• c-chart
• u-chart

Correct Answer: X-bar chart

Q2. What does a process being ‘in statistical control’ imply in the context of pharmaceutical production?

• The process always meets product specifications
• Only common causes of variation are present and the process is stable
• The process has no variation at all
• Special causes are frequently shifting the mean

Correct Answer: Only common causes of variation are present and the process is stable

Q3. Which index measures how centered a process is relative to the specification limits?

• Cp
• Cpk
• Pp
• Ppk

Correct Answer: Cpk

Q4. For attribute data where the subgroup size varies, which control chart is most appropriate to monitor defects per unit?

• p-chart
• np-chart
• c-chart
• u-chart

Correct Answer: u-chart

Q5. What is the primary purpose of rational subgrouping when constructing control charts?

• To increase sample size for more precise estimates
• To ensure within-subgroup variation represents common cause variation while between-subgroup variation can reveal special causes
• To randomize the sampling schedule
• To ensure all subgroups have identical means

Correct Answer: To ensure within-subgroup variation represents common cause variation while between-subgroup variation can reveal special causes

Q6. Which control chart is suitable for monitoring the number of defects per container when the area or volume inspected is constant?

• c-chart
• p-chart
• X-bar chart
• R-chart

Correct Answer: c-chart

Q7. Which of the following is TRUE about control limits versus specification limits?

• Control limits are determined by customer requirements and specification limits are statistical
• Control limits indicate inherent process variation; specification limits indicate customer or regulatory requirements
• Both limits are always numerically identical
• Specification limits change daily while control limits are fixed

Correct Answer: Control limits indicate inherent process variation; specification limits indicate customer or regulatory requirements

Q8. When subgroup size is 1 and individual measurements are evaluated, which chart pairs appropriately with the X-chart?

• S-chart (standard deviation chart)
• R-chart (range chart)
• Moving range (MR) chart
• p-chart

Correct Answer: Moving range (MR) chart

Q9. Which run rule is commonly used to detect small sustained shifts in the process mean?

• One point beyond 3-sigma control limits
• Two out of three successive points beyond 2-sigma on the same side
• Single point at the centerline
• All points within 1-sigma band

Correct Answer: Two out of three successive points beyond 2-sigma on the same side

Q10. Which control chart method gives more sensitivity to small shifts and uses exponentially weighted moving averages?

• CUSUM chart
• X-bar chart
• EWMA chart
• p-chart

Correct Answer: EWMA chart

Q11. What is the Average Run Length (ARL) in SPC?

• Average number of defects per unit
• Average number of samples taken before process capability is computed
• Average number of points plotted before an out-of-control signal occurs
• Average number of subgroups required to estimate sigma

Correct Answer: Average number of points plotted before an out-of-control signal occurs

Q12. Which technique is best when data are highly skewed and normality assumption for X-bar chart is violated?

• Ignore skewness and use X-bar chart anyway
• Use a transformation (e.g., Box-Cox) or use nonparametric control charts
• Decrease subgroup size to 1 always
• Switch to a p-chart

Correct Answer: Use a transformation (e.g., Box-Cox) or use nonparametric control charts

Q13. Which index compares overall performance including process centering and variability using actual long-term sigma?

• Cp
• Cpk
• Pp
• Ppk

Correct Answer: Ppk

Q14. In pharmaceutical SPC, what is the recommended response when a control chart signals an out-of-control point?

• Immediately stop the process and recall all batches
• Investigate assignable causes before making permanent adjustments to the process
• Ignore isolated points if product still meets specifications
• Increase subgroup size to mask variation

Correct Answer: Investigate assignable causes before making permanent adjustments to the process

Q15. Which chart is appropriate for monitoring the proportion of tablets failing dissolution in each sample of variable sample sizes?

• np-chart
• p-chart
• c-chart
• X-bar chart

Correct Answer: p-chart

Q16. Which statement best describes the difference between CUSUM and EWMA charts?

• CUSUM detects only large shifts; EWMA detects only very small shifts
• CUSUM accumulates deviations to detect persistent shifts; EWMA gives exponentially decreasing weights to past data for sensitivity to small shifts
• Both are identical in calculation and interpretation
• EWMA is used only for attribute data while CUSUM is for variables

Correct Answer: CUSUM accumulates deviations to detect persistent shifts; EWMA gives exponentially decreasing weights to past data for sensitivity to small shifts

Q17. Which of the following is a common method to estimate process sigma for control chart limits when the true sigma is unknown?

• Use the overall range-of-subgroup averages and convert to sigma using d2 constant
• Use specification limits divided by 6
• Assume sigma equals the process mean
• Use the median as sigma estimate

Correct Answer: Use the overall range-of-subgroup averages and convert to sigma using d2 constant

Q18. When monitoring rare events (very low defect rates), which chart is typically most appropriate?

• p-chart with large subgroup sizes
• c-chart
• g-chart or use time-between-failures approach
• X-bar chart

Correct Answer: g-chart or use time-between-failures approach

Q19. Which of the following indicates a false action risk (Type I error) when using control charts?

• Failing to detect a real process shift
• Signaling out-of-control when the process is actually stable
• Properly identifying assignable causes
• Adjusting the process only when multiple rules are violated

Correct Answer: Signaling out-of-control when the process is actually stable

Q20. Which practice improves the reliability of control charts in a pharmaceutical lab where measurement error is significant?

• Ignore measurement system error and chart raw data
• Conduct a Measurement System Analysis (e.g., Gage R&R) and reduce measurement variability before SPC
• Always use subgroup size of 1 to minimize measurement error
• Use c-charts for all measurements

Correct Answer: Conduct a Measurement System Analysis (e.g., Gage R&R) and reduce measurement variability before SPC

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