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# Statistical Qua-WPS Office ```Statistical Quality Control Questions and Answers – Attribute Control Charts – Process Capability
Analysis using a Histogram or a Probability Plot – 1
This set of Statistical Quality Control Multiple Choice Questions &amp; 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.
a) Analyze
b) Define
c) Control
d) Measure
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&plusmn;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?
a) Mean
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
c) p-chart
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
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
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
13. Which of these is not one of the primary techniques used to find out the process capability?
a) Histogram
b) Probability plots
c) Control charts
d) Acceptance sampling
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.
a) True
b) False
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.
a) True
b) False
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.
Statistical Quality Control Questions and Answers – Variable Charts – Control Charts for x̅ and R – 2
This set of Statistical Quality Control Multiple Choice Questions &amp; Answers focuses on “Variable Charts –
Control Charts for x̅ and R – 2”.
1. LCL for the R chart is given by __________
a) D3 R
b) D2 R
c) R – D3 R
d) d2 R
Explanation: LCL for an R chart is always given by the following equation,
LCL = D3 R.
2. In the general equation of UCL of a control chart, for any x chart, which of these is used as the
estimator of μ?
a) x&macr;
b) R&macr;
c) x&macr;&macr;
d) R&macr;&macr;
Explanation: UCL=μ+ Zα/2 σ is the general equation for UCL for any control chart. For any x&macr; chart, x&macr;&macr; is
used as the estimator of μ in the above mentioned equation.
3. Which of these gives the correct value of A2 used in the equation for control limits of a x control chart?
a) 3d2n√
b) 3n√
c) 3d2
d) 3d2√
Explanation: The value of A2 used in the equation of control limits of a x control chart is given by
following equation,
3d2n√
4. In phase I application of x and R chart, the control limits obtained from the equations are treated as
____________
a) Final limits
b) Trial limits
c) Warning limits
d) Pattern limits
Explanation: The obtained limits from the equation of control limits for a x and R chart, are generally
treated as Trial limits. They allow us to determine whether the process was in control when the m initial
samples were taken.
5. Which term is having a closest meaning as Sampling Distributions?
a) Control charts
b) On site inspection
c) Whole lot inspection
d) Acceptance sampling
Explanation: The term “control charts” is having a closest meaning to “sampling distribution” because,
control charts are also plotted on the data obtained from the sample inspection and also, they show
variation in sample data.
6. Process capability generally uses __________
a) Specifications
b) Control Limits
c) Process standard deviation
d) Mean of any one sample
Explanation: Process capability studies make use of the specifications of any certain Critical-to-quality
characteristic or quality characteristic to estimate the performance of any process.
7. The process standard deviation is given by __________
a) R/d2
b) Rd2
c) 1/d2
d) R/d
Explanation: The process standard deviation may be estimated by using the following equation,
σ^=R&macr;d2
8. For any process, the sample ranges are, 1.2,1.5,1.1,1.4,1.5. The subgroup size is 5. What will be the
process standard deviation? Given: d2=2.326 and A2=0.577
a) 0.576
b) 2.322
c) 0.511
d) 2.463
Explanation: We know that,
R&macr;=∑i=ni=0Rin and “process standard deviation = R&macr;d2“, by using the values of R and d2 in the question,
we get process standard deviation=0.576
9. A tolerance diagram is also called ____________
a) Scatter diagram
b) Defect concentration diagram
c) Histogram
d) Tier chart
Explanation: The run chart of individual observations in each sample is called the tolerance diagram for
any process. The tolerance diagram is also called Tier chart of the process.
10. Is there any relationship between specification limits and control limits of x and R charts?
a) Yes, Specification limits = Control limits
b) Yes, Control limits=Specification limits/2
c) No
d) Yes, Control limits*0.5 = Specification limits
Explanation: There is no certain relationship defined; between the control limits of x and R charts and
the specification limits of any quality characteristic.
11. Control limits are ___________
a) Limits defined by customers
b) Limits driven by the natural variability of the process
c) Limits driven by the inherent variability of the process
d) Statistical limits
Explanation: The control limits are the limits for a quality characteristic for a process to be in-control.
They are driven by the natural variability of the process.
12. The natural variability of the process is measured by ____________
a) Process mean
b) Sample standard deviation
c) Process standard deviation
d) Sample mean
Explanation: The natural variability of any process is the main factor affecting the control limits of any
quality characteristic while plotting a control chart. They are measured by process standard deviation, σ.
13. What type of chart will be used to plot the number of defectives in the output of any process?
a) x bar chart
b) R chart
c) c chart
d) p chart
Explanation: The number of defectives in the samples of the output of a process is monitored by the p
chart and the number of defects is monitored by a “c chart”.
14. Process standard deviation is necessarily equal to the sample standard deviation of the same process.
a) True
b) False