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 & 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 View Answer Answer: c 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. advertisement 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 View Answer Answer: b 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 View Answer Answer: a 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 View Answer Answer: d 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 View Answer Answer: b Explanation: For six sigma distribution of the product quality characteristic, the upper natural tolerance control limit will fall at, UNTL = μ + 3σ. advertisement 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 View Answer Answer: c 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 View Answer Answer: b 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? a) Mean b) Standard deviation c) Spread d) Design of Experiments View Answer Answer: d 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 View Answer Answer: d 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. advertisement 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 View Answer 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 View Answer 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 View Answer 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 View Answer advertisement 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 View Answer Answer: a 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 View Answer Answer: a 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 & 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 View Answer Answer: a Explanation: LCL for an R chart is always given by the following equation, LCL = D3 R. advertisement 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¯ b) R¯ c) x¯¯ d) R¯¯ View Answer Answer: c Explanation: UCL=μ+ Zα/2 σ is the general equation for UCL for any control chart. For any x¯ chart, x¯¯ 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√ View Answer Answer: a 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 View Answer Answer: b 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 View Answer Answer: a 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. advertisement 6. Process capability generally uses __________ a) Specifications b) Control Limits c) Process standard deviation d) Mean of any one sample View Answer Answer: b 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 View Answer Answer: a Explanation: The process standard deviation may be estimated by using the following equation, σ^=R¯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 View Answer Answer: a Explanation: We know that, R¯=∑i=ni=0Rin and “process standard deviation = R¯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 View Answer Answer: d 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. advertisement 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 View Answer Answer: c 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 View Answer Answer: b 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 View Answer Answer: c 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 View Answer Answer: d 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”. advertisement 14. Process standard deviation is necessarily equal to the sample standard deviation of the same process. a) True b) False View Answer Answer: b Explanation: It is not necessary that the sample standard deviation will always be equal to the process standard deviation, for a same process. This is because; there may be assignable causes of variation while the sample is being produced by the process. 15.“There is no need of revision of control limits once calculated by the equations of control limits. a) True b) False View Answer Answer: b Explanation: In the phase I application of control charts, the limits calculated from equations are used as trial limits because it gives us an idea about the variation, both, inherent and natural. So with time the variation changes, to compensate this, limits must be revised after a certain time.
