# Statistical Quality Control Questions and Answers – Process Capability Analysis Using Control Charts

This set of Statistical Quality Control Multiple Choice Questions & Answers (MCQs) focuses on “Process Capability Analysis Using Control Charts”.

1. Which one of these tells explicitly about the potential capability of the process?
a) Histogram
b) Probability plots
c) PCRs
d) Control charts

Explanation: Histogram, process capability ratios and the probability plots all can only summarize the performance of process. They don’t necessarily display the process potential capability.

2. Which one of these addresses the issue of statistical control?
a) Design of process experiments
b) Probability plots
c) Control charts
d) Histogram

Explanation: The probability plots, histogram and PCRs are just tools to summarize the process performance. They don’t address the issue of statistical control. Control charts only, are capable of doing that.

3. Which one these show that, if the systematic pattern in process output is eliminated, it would produce a lesser variability in the quality characteristic?
a) Probability plots
b) Control Charts
c) Histogram
d) PCRs

Explanation: As control charts address the issue of statistical control of the process, they ensure that there must be random patterns in the process output, so that variability is reduced.

4. Which one of these is primary technique of the process capability analysis?
a) Histogram
b) Process capability ratios
c) Probability plots
d) Control charts

Explanation: As control charts are main technique to reduce variability, by taking the statistical control into consideration, control charts are regarded as the primary technique of the process capability analysis.

5. Which chart should be used, if possible?
a) x & R Charts
b) u Charts
c) p Charts
d) c Charts

Explanation: As x & R charts are the variable control charts and the others are attribute control charts, taking the fact “variable charts give better information than the others” into consideration, x & R charts are favored over the others.
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6. Which one of these charts doesn’t need the specification of the quality characteristic?
a) x & R Charts
b) p-charts
c) c-charts
d) u-charts

Explanation: The variable control charts don’t need the specification of the quality characteristic, so x & R charts don’t need the specifications of the quality characteristic.

7. Which one of these helps us to find both instantaneous and the variability across time variability?
a) p-charts
b) np-charts
c) x & R Charts
d) c-charts

Explanation: The charts for x & R are quite useful in determination of the instantaneous and the variable across time variability of a quality characteristic.

8. What is the second name of instantaneous variability?
a) Long term variability
b) Short term variability
c) Long distance variability
d) Variability across time

Explanation: Instantaneous variability is the variability for a small tenure of process operation. It is also known as the short term variability.

9. Which one of these is similar to the long-term variability?
a) Instantaneous variability
b) Variability across time
c) Large variability
d) Large distance variability

Explanation: The variability across time phrase is also known as the long term variability, as this phrase is used for the variability calculated for a big interval of time.

10. Which control charts will be useful if the process output data for the process capability study are collected in different time periods?
a) x & R Charts
b) p-charts
c) c-charts
d) u-charts

Explanation: As variable control charts are capable of determining the process capability of both types, i.e. the instantaneous variability, and the variability across time, they are used, when the data for process capability analysis is collected in different shifts.

11. If the Cpl of a safety-related parameter, is 0.69, what can we say about the process capability?
a) Process is capable
b) Process is not capable
c) Process is capable but will become not-capable in sooner time
d) Process is not-capable but will become capable in sooner time

Explanation: For a safety-related parameter, we know that the one-sided process capability ratio must be greater than, 1.50 for an existing process, or 1.67 for a new process. So the above mentioned process capability is inadequate.

12. Which one of these can be used as the monitoring device to show the effect of changes in the process on process performance?
a) Control charts
b) Designed experiments
c) Histogram
d) Probability plots

Explanation: Control charts give the time to time data about the process output in a visual display. So we can use them as a monitoring device to show the effect of changes in the process, on process performance.

13. If Cpu=1.82 for strength quality characteristic for a new process, can we use the process?
a) Process is capable
b) Process is not capable
c) Process is capable but will improve in sooner time
d) Process is not capable but will improve in sooner time

Explanation: As strength is a safety parameter, the minimum value for Cpu for it for a new process is 1.67. So we can use the above mentioned new process.

14. p-charts can be used rather than using the x & R charts, in the case of variable time spans of data collection.
a) True
b) False

Explanation: As variable charts are more capable of finding the process capability to analyze both instantaneous variability and the variability across time, x & R charts are more used instead of p-charts.

15. Histograms explain the process statistical control better than the control charts.
a) True
b) False

Explanation: As control charts are real time representation of the quality characteristic of process output according to time, they explain the process statistical control better than any other method.

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