Process capability analysis MCQs With Answer

Process capability analysis MCQs With Answer

This quiz set is designed for M.Pharm students studying Quality Management Systems (MQA 102T) to deepen understanding of process capability analysis — a key tool for ensuring pharmaceutical manufacturing consistently meets specification limits. The questions cover theory, indices (Cp, Cpk, Pp, Ppk), assumptions (normality, stability), measurement system effects, sample size considerations, regulatory context, and practical interpretation in a pharma setting. Each MCQ is crafted to reinforce calculation concepts, decision-making for capability improvement, and pitfalls commonly seen in industry. Use these questions for self-assessment or classroom discussion to strengthen your ability to evaluate and improve process performance in regulated environments.

Q1. What is the primary purpose of process capability analysis in pharmaceutical manufacturing?

• To determine whether a process is stable with respect to control limits
• To quantify how well a stable process can produce products within specified limits
• To validate analytical methods used in quality control
• To calculate batch release times and costs

Correct Answer: To quantify how well a stable process can produce products within specified limits

Q2. Which formula correctly defines the Cp (process capability) index?

• Cp = (USL − LSL) / (6 × σ)
• Cp = min(USL − μ, μ − LSL) / (3 × σ)
• Cp = (USL − LSL) / (3 × σ)
• Cp = (USL − μ) / (3 × σ)

Correct Answer: Cp = (USL − LSL) / (6 × σ)

Q3. How is Cpk (process capability index accounting for centering) calculated?

• Cpk = (USL − LSL) / (6 × σ)
• Cpk = min[(USL − μ), (μ − LSL)] / (3 × σ)
• Cpk = (USL − μ) / (6 × σ)
• Cpk = max[(USL − μ), (μ − LSL)] / (3 × σ)

Correct Answer: Cpk = min[(USL − μ), (μ − LSL)] / (3 × σ)

Q4. What distinguishes Pp from Cp in capability analysis?

• Pp uses within-subgroup (short-term) standard deviation, Cp uses overall (long-term) standard deviation
• Pp uses overall (long-term) standard deviation, Cp uses within-subgroup (short-term) standard deviation
• Pp and Cp are identical indices with different names
• Pp adjusts for non-normal data while Cp assumes normality

Correct Answer: Pp uses overall (long-term) standard deviation, Cp uses within-subgroup (short-term) standard deviation

Q5. Ppk differs from Cpk in that Ppk uses which of the following?

• Short-term standard deviation (within-subgroup)
• Overall (long-term) standard deviation
• Only the process mean without considering variability
• The maximum of upper and lower capability ratios

Correct Answer: Overall (long-term) standard deviation

Q6. In pharmaceutical industry practice, which Cpk value is commonly considered the minimum desirable for an established process?

• Cpk ≥ 0.67
• Cpk ≥ 1.0
• Cpk ≥ 1.33
• Cpk ≥ 2.0

Correct Answer: Cpk ≥ 1.33

Q7. Which prerequisite must be satisfied before performing a process capability study?

• The process must be under statistical control (stable)
• The process must have a Cpk ≥ 1.33 already
• All measurement instruments must be brand new
• Batch size must exceed 1000 units

Correct Answer: The process must be under statistical control (stable)

Q8. For a normally distributed process, approximately what percentage of measurements fall within ±3σ of the mean?

• 68.27%
• 95.45%
• 99.73%
• 99.99%

Correct Answer: 99.73%

Q9. If Cp > Cpk for a given measurement, what does this typically indicate about the process?

• The process variability is too high and must be reduced
• The process spread is acceptable but the mean is not centered within specifications
• The process is non-normal and indices are invalid
• The measurement system is inadequate

Correct Answer: The process spread is acceptable but the mean is not centered within specifications

Q10. In measurement system analysis (MSA) for capability studies, which guideline is generally used to judge acceptability of measurement variation contribution?

• Measurement variation should be < 1% of process variation
• Measurement variation contribution < 10% of total variation is acceptable
• Measurement variation can be ignored for capability studies
• Measurement variation contribution must exceed 30% to be acceptable

Correct Answer: Measurement variation contribution < 10% of total variation is acceptable

Q11. Which statement best describes the difference between control charts and capability studies?

• Control charts assess stability over time; capability studies quantify performance relative to specification limits
• Control charts calculate Cp and Cpk; capability studies only check for outliers
• Control charts are used only for laboratory tests; capability studies are for manufacturing
• There is no practical difference between them

Correct Answer: Control charts assess stability over time; capability studies quantify performance relative to specification limits

Q12. If process data are markedly non-normal, which approach is most appropriate for capability assessment?

• Proceed with Cp/Cpk without adjustment; results are always valid
• Use data transformation (e.g., Box-Cox) or non-parametric capability methods
• Discard the data and re-run the entire process
• Increase sample size to 5 measurements only

Correct Answer: Use data transformation (e.g., Box-Cox) or non-parametric capability methods

Q13. Why is within-subgroup (short-term) standard deviation often used to calculate Cp?

• It reflects long-term variability including shifts and drifts
• It isolates short-term inherent process variation by excluding between-subgroup effects
• It is always larger than overall standard deviation
• It is required by regulatory agencies for all calculations

Correct Answer: It isolates short-term inherent process variation by excluding between-subgroup effects

Q14. For a reliable capability estimate, which sample size practice is commonly recommended?

• Use a single sample of size 3 measured once
• Collect as many samples as practical; a common minimum recommendation is around 30 subgroup means or 30–50 individual measurements
• Only one batch is sufficient for capability assessment
• Sample size is irrelevant if Cp and Cpk are calculated

Correct Answer: Collect as many samples as practical; a common minimum recommendation is around 30 subgroup means or 30–50 individual measurements

Q15. Which statement correctly contrasts Cp/Cpk with Pp/Ppk?

• Cp and Cpk use overall sigma while Pp and Ppk use within-subgroup sigma
• Cp and Cpk measure short-term capability; Pp and Ppk measure long-term performance including between-subgroup variation
• Cp and Cpk are non-parametric indices while Pp and Ppk assume normality
• There is no difference; they are interchangeable

Correct Answer: Cp and Cpk measure short-term capability; Pp and Ppk measure long-term performance including between-subgroup variation

Q16. Which combination of actions will most directly improve a low Cpk for a pharmaceutical critical quality attribute?

• Increase sample frequency and change control chart limits
• Center the process mean on the midpoint of specification and reduce process variability
• Relax the specification limits to match the current mean
• Switch from Cp/Cpk to Pp/Ppk indices only

Correct Answer: Center the process mean on the midpoint of specification and reduce process variability

Q17. If a process is in statistical control (no special causes) but has Cpk < 1, what is the interpretation?

• The process is both stable and capable
• The process is stable but not capable of meeting specification limits
• The process is incapable because it is out of control
• The process requires no action because control and capability are unrelated

Correct Answer: The process is stable but not capable of meeting specification limits

Q18. A centered process with Cpk = 1 corresponds approximately to what defect proportion (nonconforming) assuming normality?

• About 50% nonconforming
• About 0.27% nonconforming (≈ 2700 ppm)
• About 0.00034% nonconforming (≈ 3.4 ppm)
• Zero defects

Correct Answer: About 0.27% nonconforming (≈ 2700 ppm)

Q19. Which ICH guideline most directly supports the principles of Quality by Design (product and process understanding) relevant to capability studies?

• ICH Q7
• ICH Q8
• ICH Q6A
• ICH Q4B

Correct Answer: ICH Q8

Q20. If Pp is substantially greater than Ppk for the same dataset, what is the most likely cause?

• The process is perfectly centered relative to the specifications
• The process mean is shifted away from the midpoint of specification limits (lack of centering)
• The overall variability is much smaller than short-term variability
• The specification limits are symmetric around the mean

Correct Answer: The process mean is shifted away from the midpoint of specification limits (lack of centering)

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