This set of Statistical Quality Control Multiple Choice Questions & Answers (MCQs) focuses on “Attribute Charts – Choice between Attributes and Variable Control Charts – 1”.
1. The number of defects per unit of a casting process output, is plotted on _____________ chart.
a) x bar
Explanation: The average number of defects or nonconformities per unit of a process output is always plotted on a u-chart or the control chart for average number of nonconformities per unit.
2. What type of control chart can be used to plot “number of defectives in the output of a process for making a machine part” data?
Explanation: The p-chart or the Control Chart for Fraction Nonconforming is used to plot “the number of defectives in the output of any manufacturing process” data, on a control chart.
3. Which of the control chart is used to find out variability in the data?
Explanation: s-chart or the control charts based on the sample standard deviation, are a useful method to find out the variability in the data. They are only used for Variable data, not for attribute data.
4. Which of the charts are more efficient to find out variability in the data when the sample size is more than 10?
Explanation: To find out variability in the data, R-charts and s-charts are used. But when the sample size is more than 10 or 12, the efficiency of s-charts to find variability in the data, is more than the R-charts.
5. Which of these is an advantage of attribute control chart?
a) Much useful information about the process performance can be gathered
b) Mean and variability is obtained directly
c) One quality characteristic is observed at a time
d) Several quality characteristics can be considered jointly
Explanation: The attribute control charts have a main advantage of consideration of many quality characteristics to be jointly analyzed. This is because a defect can be produced by one or more quality characteristics, which are out of control.
6. Which of these is an advantage of variable control chart?
a) Numerous quality characteristics considered at a time
b) To achieve the information very easily about the mean and variability
c) To have analyses of units nonconforming
d) To analyze the defects in one unit
Explanation: The main advantage of a variable control chart is that they provide much useful information about the process performance. They give more functional information about the process mean and variability.
7. X bar and R charts are __________ indicators of trouble.
Explanation: x and R charts are leading indicators of trouble in the process. We conclude this because; they indicate the out-of-control process before the process has made defective products, unlike p-chart, which indicates the out-of control process after the process has made defectives.
8. The efficiency of variable control charts is _________ the efficiency of the p-charts when p is small and far away from 0.5.
a) Lesser than
b) More than
c) Equal to
Explanation: The efficiency of variable control charts is considerable higher than the efficiency of the p-charts when the value of p is small or away from 0.5.
9. The efficiency of p-charts is __________ the efficiency of the x bar and R charts when p is closer to 0.5.
a) Equal to
b) More than
c) Less than
Explanation: The efficiency of p-charts become higher or just more than the efficiency of x-bar and R charts, when the value of p comes closer to 0.5 or higher than 0.5.
10. Which of these is most economical in long term?
a) x And R charts
Explanation: The variable charts are more economical in long term, because they indicate process state out-of-control, before we have paid to make a nonconforming product. Attribute charts become costly because the same indication from them comes, when defectives are already produced.
11. When a change in product specification is desired, which of these control charts should be used?
b) x And R charts
Explanation: The variable control charts should be used whenever a new process is coming on stream, or a new product is being manufactured by an existing process, or a change in product specification is desired.
12. When we want to troubleshoot the out-of-control process, we use _________ control charts.
Explanation: Whenever a process is out-of-control and it is known to us, we use variable control charts to troubleshoot the process. It is because; we can focus on each quality characteristic individually using variable control charts.
13. In regulated industries, where process stability and process capability must be continually demonstrated __________ charts are used.
a) x And s
Explanation: A regulated industry needs continuous information about the process stability and capability. As variable control charts are more efficient to find out these, they are used in the regulated industries.
14. Before choosing which CTQ-characteristic to be controlled, control chart must be chosen.
Explanation: We cannot decide whether to use a variable control chart or an attribute control chart before choosing a quality characteristic. This is because attribute charts are only plotted for attribute data.
15. Proper type of control charts to be prepared, must be chosen after choosing the point in the process at which the control charts will be implemented.
Explanation: It is necessary to point out the location where the charts will be implemented, before choosing the control charts to be prepared. This is because the location of implementing charts can reveal more important factors to be considered while choosing the proper control chart.
Sanfoundry Global Education & Learning Series – Statistical Quality Control.
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