This set of Statistical Quality Control Multiple Choice Questions & Answers (MCQs) focuses on “Attribute Control Charts – Process Capability Analysis using a Histogram or a Probability Plot – 1”.
1. Process capability refers to ___________
a) Changes in process
b) Variability in process
c) Uniformity in process
d) Unevenness in process
Explanation: Process capability refers to the uniformity of the process. This uniformity in the process is always measured in the terms of the variability in the processs.
2. The process of usage of statistical methods to determine the variability in a process and to reduce or completely eliminating the variability, is called ________________
a) Process capability
b) Process capability Analysis
c) Process variability
d) Process variability analysis
Explanation: The method of using the statistical methods to determine the variability in a process and to reduce it to the minimum level, is generally known as the Process Capability Analysis.
3. Determining process capability is an important part of _____________ step of DMAIC process.
Explanation: Determining process capability is an important part of analyze step of DMAIC process. It is generally done in the analyze step majorly but it is also used in improve step.
4. Which of these is used as the measure of process capability?
a) Process mean
b) Process standard deviation
c) Sample standard deviation
d) Six-sigma spread in the distribution of the product quality characteristic
Explanation: It is customary to take the six – sigma distribution of the product quality characteristic, as the measure of the process capability, in the process capability analysis.
5. For a six–sigma spread in the distribution of the product quality characteristic, the upper natural control limit will fall at _____________
a) μ + 2σ
b) μ + 3σ
c) μ + 4σ
d) μ + 6σ
Explanation: For six sigma distribution of the product quality characteristic, the upper natural tolerance control limit will fall at,
UNTL = μ + 3σ.
6. μ – 3σ, is the LNTL for ______________
a) 3-sigma spread in distribution of CTQ characteristic
b) 1-sigma spread in distribution of CTQ characteristic
c) 6-sigma spread in distribution of CTQ characteristic
d) 4-sigma spread in distribution of CTQ characteristic
Explanation: The six-sigma spread in the distribution of the CTQ characteristic of a process, is generally having its lower natural tolerance limit at,
LNTL = μ – 3σ.
7. 0.27 percent outside the normal tolerances can be obtained using ____________
a) 6-sigma both sides of mean
b) 3-sigma both sides of mean
c) 2-sigma both sides of mean
d) 8-sigma both sides of mean
Explanation: When there is NTL (s) of μ±3σ, i.e. 3-sigma both sides of the mean of the variable, the 99.73% products are between the specification limit. So there are 0.27% outside the normal tolerances.
8. Which of these is not necessary to find the process capability?
b) Standard deviation
d) Design of Experiments
Explanation: In the process capability analysis, we need to have the following to start the study; mean of the process, spread or the standard deviation of the process, and the specified shape of the probability distribution.
9. When we don’t have the mean, spread and the shape of probability distribution of one CTQ characteristic of a process, we can use ___________ for process capability analysis.
a) Acceptance sampling
b) Design of experiment
d) Specifications on the quality characteristic
Explanation: In case we don’t have any information about the mean, spread and the shape of the probability distribution of one CTQ characteristic of a process, we can use specifications on the CTQ characteristic.
10. Which of these is not a major use of the PCA (Process Capability Analysis)?
a) Prediction of how well the process will hold the tolerances
b) Reduction of variability in process
c) Establishing an interval between sampling
d) Stating the need of the Acceptance sampling
Explanation: PCA or the Process Capability Analysis is used to predict how well the process will hold the tolerance and to reduce the variability. It also gives us an interval between sampling.
11. When in PCA, we have only the sample unit of product without any direct observation of the process or the time history of the production, the PCA is also called ____________
a) Product inspection
b) Product characterization
c) Product sampling
d) Process design
Explanation: In the studies of PCA, when we have availability of only the sample units of product without any direct observation of the process or the time history of the production, PCA study is now called Product Characterization.
12. In product characterization, we cannot say anything about _____________
a) Dynamic behavior of the process
b) Distribution of quality characteristic
c) Process yield
d) Fraction conforming to specifications
Explanation: In product characterization, we can only state the process yield information or the information about the distribution of the product quality characteristic or the fraction conforming to specifications data.
13. Which of these is not one of the primary techniques used to find out the process capability?
b) Probability plots
c) Control charts
d) Acceptance sampling
Explanation: Histogram or probability plots, control charts and designed experiments are the 3 primary techniques used to find out process capability.
14. Product characterization cannot be used for the determination of the state of the statistical control of the process by which, the products are made.
Explanation: During product characterization, we do not have the historical data of production and the direct observation on the process. So we cannot say anything about the state of the process making the products to be characterized.
15. Process capability can be expressed as a percentage outside of the specifications.
Explanation: We use the process mean, spread, and the shape of the probability plot of the quality characteristic for the estimation of Process Capability. Alternatively, Process capability can be expressed as a percentage outside of the specifications.
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