OM- chapter 10

When a process is judged out of control for an important characteristic, what corrective action should be taken? A. The process should be stopped and corrective action must be taken. B. The process should be investigated for Type I error. C. The process should be investigated for Type II error. D. The process should continue, however, 100% inspection is required. E. The process should continue until another sample is taken.

The process should be stopped and corrective action must be taken

The range chart (R-chart) is most likely to detect a change in: A. proportion. B. mean. C. number defective. D. process variability. E. sample size.

process variability

Which of the following quality control sample statistics measures a quality characteristic which is an attribute? A. Mean B. Variance C. Standard deviation D. Range E. Proportion

proportion

What should managers have in place if a point is observed that is outside the control limits, or a run test produces a large z-value? A. Taking more samples B. Revised sample plan C. Revisions to the control chart D. Recall plans E. Response plans

response plans

The term "2 sigma limits" in the context of a control chart refers to the variability of the: A. process. B. population. C. sample. D. sampling distribution.

sampling distribution

The probability of concluding that an assignable variation exists when only random variation is present is: A. Statistical shift B. Specification variation C. Control limit error D. Type I error E. Type II error

type 1 error

Variation in a sample statistic collected from a process may be either random variation or assignable variation.

true

When a process is not centred, its capability should be based on Cpk because it considers the upper and lower design specifications separately and not just the overall design specification width.

true

If he uses upper and lower control limits of 520 and 480 hours, what is his risk (alpha) of concluding service life is out of control when it is actually under control (Type I error)? A. 0.0026 B. 0.0456 C. 0.3174 D. 0.6826 E. 0.9544

0.0456

What is the standard deviation of the sampling distribution of sample means? A. 5 hours B. 6.67 hours C. 10 hours D. 11.55 hours E. 20 hours

10 hours

Studies on a bottle-filling machine indicates it fills bottles to a mean of 16 ounces with a standard deviation of 0.10 ounces. Assuming the Cpindex = 1.0, what is/are the process specification(s)? A. 0.10 ounces. B. 0.60 ounces. C. 16.0 ounces plus or minus 0.60 ounces. D. 16.0 ounces plus or minus 0.30 ounces.

16.0 ounces plus or minus 0.30 ounces

For a process to be capable, it must have a capability ratio of at least 1.00. A ratio of 1.00 implies that what percent of the output of a process can be expected to be within the design specification limits? A. 66.67% B. 73.33% C. 95.54% D. 99.74% E. 100%

99.74%

The six sigma quality improvement methodology is called: A. PDSA B. DMAIC C. 5W2H D. continuous improvement system.

DMAIC

Using three sigma control limits (rather than two sigma limits) tends to have what impact on error probabilities? A. Increase the Type II and decrease the Type I. B. Decrease the Type II and increase the Type I. C. Decrease the Type I and Type II. D. Increase the Type I and Type II. E. Have little or no impact.

Increase the Type II and decrease the Type I.

For which of the following would a p-chart be used? A. Monitor the process means for samples. B. Monitor dispersion in sample data. C. Monitor the proportion of defectives in a sample .D. Monitor the number of defects per unit. E. Monitor the range of values in samples.

Monitor the proportion of defectives in a sample

Which statement is an accurate description of a process that is "capable"? A. No random variation is evident, only assignable variation. B. Process variability is greater than variation allowed by design specifications. C. Process variability is less than variation allowed by design specifications. D. Assignable variation is less than random variation. E. Assignable variation is greater than random variation.

Process variability is less than variation allowed by design specifications

Nonrandom variation is indicated when a point is observed that is outside the control limits, or a run test produces a large z-value. What is this a sign of? A. Excessive random variation B. Assignable variation C. The process is in control D. The control limit is incorrect E. More samples are required.

assignable variation

Too many observations on one side of the centre line on a run chart is an indication of what? A. cycles B. trend C. bias D. level shift E. too much dispersion

bias

A control chart used to monitor the number of defects per unit is the: A. p-chart. B. R-chart C. x-bar chart. D. c-chart. E. Gantt chart.

c-chart

As the sample size increases, the distribution of sample averages approaches a Normal distribution regardless of the shape of the sampled population. This is identified in which of the following? A. Assignable variation B. Random variation C. Central limit theorem D. Type I errors E. Mean charts

central limit theorem

This involves performing experiments by changing levels of factors to measure their influence on output and identifying best levels for each factor. A. Process capability indexes B. Design of experiments C. Six sigma quality D. Assignable variation influence E. Run tests

design of experiments

The purpose of control charts is to: A. estimate the proportion of output that is acceptable. B. inspect the quality of all outputs from a process. C. determine if the output of a process is within specifications. D. distinguish between random variation and assignable variation in a process.

distinguish between random variation and assignable variation in a process.

Which of the following is not a step in the quality control planning process? A. Define the quality characteristic to be controlled. B. Determine a quality control point in the process. C. Eliminate all defects found. D. Plan how inspection is to be done. E. Plan corrective action

eliminate all defects found

A c-chart is used to monitor the number of defectives in the output of a process.

false

A p-chart is used to measure shifts in process dispersion.

false

A process capability index (Cp) of 0.70 indicates that a process is capable of producing to design specifications.

false

A sample statistic that falls inside the control limits suggests there is assignable variation in the process.

false

Approximately 99.7% of sample means will fall within two standard deviations of the process mean.

false

As a rule of thumb, operations with a high proportion of human involvement necessitate less inspection than mechanical operations, which tend to be less reliable.

false

Attributes are process characteristics that must be measured rather than counted.

false

Concluding that a process has changed when it has not is known as a Type II error.

false

Concluding that a process has not changed when it has is known as a Type I error.

false

Control limits are determined based on design specification limits.

false

Control limits are specifications established by engineering design or customer requirements.

false

Control limits distinguish between non-random and assignable variability.

false

Design of experiments involves performing experiments to determine the best control limits for a process.

false

Design specifications are equivalent to control limits.

false

Low-cost, high-volume items typically require relatively low levels of inspection.

false

Sample range control charts are used to measure shifts in the process mean.

false

The end of a manufacturing process is always the best place for a quality inspection point.

false

The frequency and quantity of inspection depends primarily on the cost of inspection.

false

The optimum level of inspection occurs when the cost of passing defectives is minimized.

false

The part of statistical quality control that occurs during the production process is known as acceptance sampling.

false

The primary purpose of statistical process control is to detect defects in finished products before they are shipped to customers.

false

The process capability index, indicated by Cpk is used only when the process is centred.

false

The variability of a process output is equivalent to the distribution of sample means of that process output for any sample size taken from the process.

false

Typically the production of high-cost, low-volume items require little quality control inspection.

false

process variability is a key factor in process capability.

false

A point that plots below the lower control limit on the range chart: A. should be ignored because lower variation is desirable. B. should be investigated for random variation. C. may be an indication that process variation has decreased D. is not possible E. is due to a shift in the process mean

may be an indication that process variation has decreased

The DMAIC methodology involves all EXCEPT which of the following? A. Define B. Model C. Analyze D. Improve E. Control

model

A c-chart is used for: A. means. B. ranges. C. percent defective. D. fraction defective per unit. E. number of defects per unit.

number of defects per unit

A control chart used to monitor the fraction of defectives generated by a process is the: A. p-chart. B. R-chart. C. x-bar chart. D. c-chart. E. Gantt chart.

p-chart

A point which is outside of the lower control limit on an R-chart: A. is an indication that no process variation is present. B. should be ignored because it signifies very low process variation. C. should be investigated because it could indicate improvements in the methods used in a process. D. should be ignored unless another point is outside that limit. E. is impossible because the lower limit is always zero.

should be investigated because it could indicate improvements in the methods used in a process.

When using control charts sample frequency is important Sampling frequency can be a function of the ______ of a process and the _____ to sample. A. cost; cost B. frequency; cost C. frequency; time D. stability; cost E. stability; time

stability; cost

Which of the following is not needed to calculate sample mean control charts? A. A choice for z, the standard normal deviate (usually 2 or 3). B. The standard deviation of the sampling distribution .C. The sample range. D. The average of sample means (grand mean).

the sample range

When using a capability index which value determines the capability of the process? A. The smaller of the two calculations B. The larger of the two calculations C. The average of the calculations D. The largest minus the smallest E. The largest divided by the smallest

the smaller of the two calculations

The charted values on a run chart are too spread out. This is an indication of what? A. bias B. cycles C. level shift D. Too much dispersion E. trend

too much dispersion

The optimum level of inspection for quality control is where the: A. cost of inspection is minimum. B. cost of passing defectives is minimum. C. total cost of inspection and passing defectives is maximum. D. total cost of inspection and passing defectives is minimum. E. difference in inspection and defectives costs is minimum.

total cost of inspection and passing defectives is minimum

A c-chart is used to monitor the number of defects per unit of a process output.

true

A p-chart is used to monitor the fraction of defectives in the output of a process.

true

A process is "capable" if the process output falls within the design specification.

true

A sample statistic that falls outside the control limits suggests that the process mean has changed.

true

Appraisal of a good or service against a standard is called inspection.

true

Assignable variation is variation due to a specific cause, such as tool wear.

true

Concluding that a process has changed when it has not is known as a Type I error.

true

Control charts based on attribute data are for process characteristics that are counted rather than measured.

true

Control limits and process variability are directly related.

true

Control limits are statistical limits that reflect the extent to which sample statistics such as means and ranges can vary due to random variation alone.

true

Even when the sample size is fairly small, the sampling distribution can be assumed to be approximately normal even if the underlying process distribution is not normally distributed.

true

If a point on a control chart falls outside one of the control limits, this suggests that the process output is non-random, assignable variation.

true

In order for a process to be capable, it must have a capability ratio of at least 1.00.

true

Process capability" compares "process variability" to the "design specifications".

true

Quality control efforts that occur during production are referred to as statistical process control.

true

Sample range control charts are used to monitor process dispersion.

true

Six sigma quality refers to achieving process variation so small that the half-width of the design specification equals six times the standard deviation of the process.

true

Statistical process control is based on comparing periodic samples from a process to predetermined limits.

true

The amount of inspection can range from no inspection at all to inspecting each item numerous times.

true

The amount of inspection needed is governed by the costs of inspection and the expected costs of passing defective items.

true

The main task in process control is to distinguish assignable from random variation.

true

The number of defective parts in a sample is a process characteristic that is counted rather than measured.

true

The optimum level of inspection minimizes the sum of inspection costs and the cost of passing defectives.

true

The output of a process may not conform to design specifications even though the process may be statistically "in control".

true

The probability of a Type I error is the probability of concluding that assignable variation is present even though only random variation exists.

true

The process capability index, indicated by Cp is calculated as the ratio of the design specification width to the process width.

true

The sample size chosen for control charts depends on the cost of inspection versus the expected cost of Type II error.

true

The sampling distribution of sample means taken from a process has less variability than the distribution of the process.

true

There is no direct link between design specifications and statistical process control limits.

true

When using control charts sample size is important. Smaller samples are more likely to reveal a process change because a change is more likely to take place ______ the large sample, rather than ________ small samples. A. outside, outside B. outside, inside C. exclusive to, inside, D. between, outside E. within, between

within, between

A control chart used to monitor the process mean is the: A. p-chart B. R-chart C. x-bar chart D. c-chart E. Gantt chart

x-bar chart

A shift in the process mean for a measured quality characteristic would most likely be detected by a(n): A. p-chart B. x-bar chart C. c-chart D. R-chart E. s-chart

x-bar chart