Chapter 10 Operations Management
Range charts are used mainly with attribute data.
False
A plot below the lower control limit on the range chart:
II and III, may be an indication that process variation has decreased, should be investigated for assignable cause
The amount of inspection needed depends on ________ and ________.
the costs of inspection, the costs of passing on defective items
A p-chart would be used to monitor:
the fraction defective
Which of the following relationships must always be incorrect?
tolerances > control limits > process variability
The traditional view is that the optimum level of inspection is where the:
total cost of inspection and defectives is minimum
A c-chart is used to monitor the number of defects per unit for process output.
true
A lower control limit must by definition be a value less than an upper control limit.
true
A p-chart is used to monitor the fraction of defectives in the output of a process.
true
A run test checks a sequence of observations for randomness.
true
Attribute data are counted, variable data are measured.
true
Concluding that a process is out of control when it is not is known as a Type I error.
true
Control limits tend to be wider for more variable processes.
true
High-cost, low-volume items often require careful inspection since we may have large costs associated with passing defectives.
true
If a point on a control chart falls outside one of the control limits, this suggests that the process output is non-random and should be investigated.
true
Patterns of data on a control chart suggest that the process may have non-random variation.
true
Process capability compares process variability to the tolerances.
true
Run tests are useful in helping to identify nonrandom variations in a process.
true
The amount of inspection needed is governed by the costs of inspection and the expected costs of passing defective items.
true
The amount of inspection we choose can range from no inspection at all to inspecting each item numerous times.
true
The output of a process may not conform to specifications even though the process may be statistically "in control."
true
The purpose of quality control is making sure that processes are performing in an acceptable manner.
true
The sampling distribution can be assumed to be approximately normal even when the underlying process distribution is not normally distributed.
true
The traditional view is that the optimum level of inspection minimizes the sum of inspection costs and the cost of passing defectives.
true
The variation of a sampling distribution is less than the variation of the underlying process distribution.
true
When a process is not centered, its capability is measured in a slightly different way. The symbol for this case is Cpk.
true
Organizations should work to improve process capability so that inspection efforts can become more:
unnecessary
The range chart (R-chart) is most likely to detect a change in:
variability
A control chart used to monitor the process mean is the:
x-bar chart
A shift in the process mean for a measured characteristic would most likely be detected by a(n):
x-bar chart
Statistical process control charts are not really used to fix quality so much as they are used to:
alert when corrective action is needed
Inspection is a(n)________ activity.
appraisal
________ variation is a variation whose cause can be identified.
assignable
The greater the volume of the process being targeted for inspection, the more attractive ________ inspection is.
automated
A control chart used to monitor the number of defects per unit is the:
c-chart
A process results in a few defects occurring in each unit of output. Long-run, these defects should be monitored with:
c-charts
A time-ordered plot of sample statistics is called a(n) ________ chart.
control
A time-ordered plot of representative sample statistics is called a(n):
control chart
The purpose of control charts is to:
distinguish between random variation and assignable variation in the process
Which of the following is not a step in the control process?
eliminate each of the defects as they are identified
A c-chart is used to monitor the total number of defectives in the output of a process.
false
A process that exhibits random variability would be judged to be out of control.
false
An R value of zero (on a range chart) means that the process must be in control since all sample values are equal.
false
An x-bar control chart can only be valid if the underlying population it measures is a normal distribution.
false
Approving the effort that occurs during the production process is known as acceptance sampling.
false
Approximately 99.7 percent of sample means will fall within plus or minus two standard deviations of the process mean if the process is under control.
false
Attributes need to be measured, whereas variable data can be counted.
false
Control limits are based on multiples of the process standard deviation.
false
Control limits used on process control charts are specifications established by design or customers.
false
Cpk can be used only when the process if centered.
false
Cpk is useful when when the process is not centered.
false
Larger samples will require wider x-bar control limits because there is more data.
false
Low-cost, high-volume items often require more intensive inspection than other types of items.
false
Processes that are in control eliminate variations.
false
Range charts and p-charts are both used for variable data.
false
Range control charts are used to monitor process central tendency.
false
Run tests give managers an alternative to control charts; they are quicker and cost less.
false
Statistical process control focuses on the acceptability of process output.
false
Statistical process control is the measurement of rejects in the final product.
false
The Taguchi loss function suggests that the capability ratio can be improved by extending the spread between the LCL and UCL.
false
The best way to assure quality is to use extensive inspection and control charts.
false
The number of defective parts in a sample is an example of variable data because it will "vary" from one sample to another.
false
The primary purpose of statistical process control is to detect a defective product before it is shipped to a customer.
false
The purpose of statistical process control is to ensure that historical output is random.
false
The traditional view is that the optimum level of inspection occur when we catch at least 98.6 percent of the defects.
false
Tolerances represent the control limits we use on the charts.
false
The more progressive a firm's approach to quality assurance, the less that company will need to rely on:
inspection
A c-chart is used for:
number of defects per unit
A control chart used to monitor the fraction of defectives generated by a process is the:
p-chart
Which of the following quality control sample statistics indicates a quality characteristic that is an attribute?
proportion
The assurance that processes are performing in an acceptable manner is the focus of:
quality control
The basis for a statistical process control chart is a(the):
sampling distribution
A point which is outside of the lower control limit on an R-chart:
should be investigated because an assignable cause of variation might be present
