This set of Statistical Quality Control Questions and Answers for Aptitude test focuses on “Process Capability Analysis using a Histogram or a Probability Plot – 2”.
1. PCA (process capability analysis) can’t be used _____
a) To determine the process state of statistical control
b) To reduce the variability in the process
c) For specifying the location of defect
d) For modifying or selecting a process
Explanation: PCA can’t be used to specify the location of defect. It can be used to determine the process state, to reduce the variability present in it and to select or modify any process.
2. How many primary techniques are there which are used in PCA?
Explanation: There are 3 primary techniques, which are used in process capability analysis. These are; histogram or probability plots, control charts, and designed experiments.
3. Which can be used as an alternative for histogram for PCA?
a) Check sheet
b) Defect concentration diagram
c) Stem-and-Leaf Plot
d) Scatter Diagram
Explanation: Stem-and-leaf plots can be used alternatively for the process capability analysis, instead of using the histogram plots. It needs almost more than 100 observations.
4. How many observations are needed at least, to plot a histogram which gives proper information about the process capability?
Explanation: There must be at least 100 observations or more, to plot a histogram or a stem-and-leaf plot to be stable enough, which gives efficient information about the process capability.
5. Which of these is needed with the histogram to estimate the process capability?
a) Acceptance sampling
b) Scatter diagram
c) Sample average
d) Check sheet
Explanation: The histogram, when used along with the sample average x and sample standard deviation s, provides the sufficient information about the process capability.
6. Which is not an advantage of histogram to check the process capability?
a) Immediate impression of process
b) Visual impression of process
c) Fast interpretation
d) Easy to find the location of defects
Explanation: By using the histogram, to determine the process capability, we can get an immediate and visual impression of process. We can also interpret the data very quickly. But it cannot tell the location of defects.
7. When the number of product units outside the LSL and the number of product units outside USL are same, the process is called?
a) Centered process with poor process capability
b) Centered process with great process capability
c) Poorly centered process with poor process capability
d) Poorly centered process with great process capability
Explanation: When the numbers of product units outside the LSL, and the USL, are same. This means the process is centered, but there are some product units lying outside the specification limits. This gives poor process capability.
8. Probability plotting is an alternative of _____ to find process capability.
a) Control charts
c) Designed experiments
d) Acceptance sampling
Explanation: Probability plotting is an alternative to the histogram to find out the capability of the process which produces the product, which is to be used in the industry.
9. Probability plotting is not used to find ______
a) The shape of distribution
b) The center of distribution
c) The spread of distribution
d) The origin of defects
Explanation: By using the probability plots instead of the histogram, find out the process capability, we can determine the shape, center, and the spread of the distribution.
10. Which is more efficient in the case of small samples to find out the shape and spread of the distribution?
b) Probability plots
c) Designed experiments
Explanation: The advantage of probability plotting is that, it is unnecessary to divide the range of the variable into class intervals, and it often produces reasonable results for moderately small samples (which histogram will not).
11. Histogram generally is a ______
a) Graphical representation of intervals of data plotted against frequency
b) Ranked data versus the sample cumulative frequency
c) Ranked data versus the frequency
d) Diagram of unit giving the location of defects
Explanation: A histogram is generally described as a graphical representation of range of data divided into intervals plotted against the frequency of data.
12. Probability plots are graph of ranked data plotted against the cumulative frequency, with a vertical scale chosen so that the cumulative distribution of assumed type is a _____
b) Straight line
Explanation: Probability plots are the graphs of the ranked data versus the sample cumulative frequency on special paper. These plots have the vertical scale so chosen, that the cumulative distribution of the assumed type is a straight line.
13. Which of these is a disadvantage of probability plot?
a) They are not an objective procedure
b) They don’t tell about the defect
c) They are hard to interpret
d) They can’t tell about mean of the data
Explanation: Probability plots are quite useful but, they have a major disadvantage that they are not an objective procedure. There can be many conclusions for same set of data.
14. Probability plots (when cumulative) are straight line.
Explanation: Probability plots are the plot of ranked data against the cumulative frequency. The cumulative probability plots are mostly straight lines.
15. When there is an interactive effect of processes on the tolerances, process capability can’t be used for the planning of production processes.
Explanation: It is the main use of process capability to plan the production processes, when there is an interactive effect of processes on the tolerances.
16. It is often desirable to supplement probability plots with more formal statistically based goodness-of-fit tests.
Explanation: There is a disadvantage of probability plots that they are not objective procedures, i.e. they give more than one conclusions of a single data. That’s why; it’s often desirable to supplement probability plots with more formal statistically based goodness-of-fit tests.
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