OMIS 430 ch 10

If the number of standard deviations is not specified when computing control charts, what is an appropriate default value?

+/-2 SD

When control charts and run tests are used together, rank the order in which actions should be taken to compute control limits for process output.

1. determine 2. compute 3. sample statistics

A six sigma process will have a process capability index equal to

2

six sigma process will have a process capability index equal to:

2.0

Though process improvement initiatives come with a cost, benefits of more capable processes may outweigh and can include which of the following?

Less need for inspection Fewer service complaints Lower warranty costs

Which of the following are measured using attributes?

Number of calls in a day Number of defects

Which of the following are examples of inspection points in service organizations?

Outgoing patient billing accuracy at medical clinic Kitchen cleanliness at fast food restaurant at shift start

What are some examples of inspection points in the service sector? (Select all applicable answers.)

Outgoing patient billing accuracy at medical clinic. Kitchen cleanliness at fast food restaurant at shift start

When a sample average falls inside the control limits, what can be concluded about the process?

Random variation is suggested and the process is probably in control.

What are some ways operations managers can improve process capability?

Reduce the process variability Upgrade or automate equipment Standardize process steps

Which of the following statements is/are correct about the sampling distribution? (

Sampling distribution is narrower than the process distribution. Sampling distribution is a plot of many sample means.

Which of the following statements is/are correct about Specifications?

Specifications are a range of values in which all units of output must fall to be acceptable. Specifications are tolerances established by Engineering and/or the Customer.

Which of the following elements are part of the calculation for the capability analysis statistic Cpk?

Take the smaller of the two calculation values for Cpk. Calculate the distance from the mean to the upper tolerance then do the same to the lower.

For a mean control chart, when the process standard deviation is not known, what is used in its place as a measure of process variability?

avg range

Run tests can reveal non-random patterns in time-ordered data. Select three patterns that might be seen.

bias trend cycles

What happens when a process is not stable?

capability index is meaningless

A mean control chart is used to check ______.

central tendency of a variable

When the results of quality control are unacceptable, what is the next step?

corrective action

What is the range control chart upper control limit formula?

d4 x avg range

What is the first step in the control process?

define in sufficient detail what is to be controlled

For c-charts, the sample average number of defects is computed by which of the following formulas?

number of defects/number of samples

When is the capability analysis statistic Cp used?

when a process is centered between the upper and lower specifications

The "average of the sample means" is also known by what term?

x double bar

What symbol or letter signifies the number of standard deviations the control limits are based on, in the formula for a mean control chart?

z

What is the difference between variable and attribute data?

Variable data is measured on a continuous scale and attribute data is counted using discrete numbers.

Managers must make a number of important decisions about the use of control charts. What are they?

What size samples to take How often samples should be taken What type of control chart to use At what points in the process to use control charts

When is the capability analysis statistic Cpk used, instead of Cp?

When a process is not centered between the upper and lower tolerances.

When the standard deviation is not known, mean control chart upper and lower control limits are computed by adding and subtracting ______ from the grand mean

a2 x average range

When the standard deviation is not known, mean control chart upper and lower control limits are computed by adding and subtracting ______ from the grand mean.

a2 x average range

What is the rationale and basis for statistical process control?

acceptable variation within probability limits

Which type of inspection occurs before and after production?

acceptance sampling

A Type I Error is referred to by what other name?

alpha risk

What characteristic is measured in a run test?

anything observable

best synonym for inspection

appraisal

Which of the following statements about Type I error is/are correct?

A Type I error's alpha risk equals the probability (area) in the two "tails." A Type I error is concluding non-randomness and being mistaken.

Select the best definition of Quality Control.

A process that measures output relative to a standard and takes action when discrepancies occur.

Select the best definition of a "run."

A sequence of observations with a certain characteristic

Which of the following statements about inspection frequency are is/are correct?

A stable process will require less frequent checks than an unstable process. The more lots being produced the more inspections are needed.

Select the best definition of a control chart

A time-ordered plot of sample statistics used to determine randomness or non-randomness.

Select all the ways quality assurance can be part of an organization's operations strategy.

Adopt continuous process improvement methods to increase customer satisfaction with product quality. Improve process capability to reduce need for inspection

Under which conditions would on-site inspection be better than off-site at a specialized test lab?

Alteration or contamination of samples during transfer to lab Need for quick inspection results due to delivery schedule

When is the nonrandom variation shown on a control chart a positive outcome?

An observation below the lower control limit on a R-chart. An observation below the lower control limit on a c-chart. An observation below the lower control limit on a p-chart.

What is the best definition of statistical process control?

Analyze data from some point in the process to determine if the process is likely to be in or out of control.

When +/- 2 standard deviation control limits are used in a process control chart, which of the below statements are true?

Approximately 95.5% of the time random data points will fall within (inside) the upper and lower control limits.

What are the different inspection points in manufacturing?

Before a costly, irreversible or covering operation/process. Finished goods after production Raw materials & purchased parts before production

Select the best definition of random variation.

Common variation inherent in a process occurring by chance.

What is the formula for Cp?

Cp = Specification Width / Process Width

Which scenario would indicate the need for off-site testing at a centralized testing facility?

Customer specifications for satellite component require dust-free, no vibration test

Simplify standardize make mistake proof automate upgrade equipment

Eliminate steps, reduce the number of parts, use modular design Use standard parts, standard procedures Design parts that can only be assembled the correct way; have simple checks to verify a procedure has been performed correctly Substitute automated processing for manual processing Replace worn-out equipment; take advantage of technological improvements

Which of the following statements about process capability is correct

For a process to be capable, the output must fall within tolerances. A capable process exhibits natural, random variability.

What are some risks of using capability indexes?

If the process output is not normally distributed, statistical inferences are incorrect. If the process is not centered but Cp is used anyway, it gives misleading indications. If the process is not stable, Cp and Cpk are meaningless

Which of the following statements is/are correct about Inspection?

Inspection involves checking for conformance against a quality standard. Inspection can occur before, during or after production.

Which is/are examples of Acceptance Sampling?

Inspection of raw material batches before production Inspection of final assembly lots after production

What does the central limit theorem tell us about the sampling distribution?

It approaches a normal distribution as sample size increases.

Which of the following is the best definition of statistical process control?

It is analysis of data from some point in the process to determine if the process is likely to be in or out of control.

How does Taguchi's belief about quality differ from the traditional view?

The cost of poor quality increases as the output approaches the specification limit.

In a control chart when a data point falls outside the control limits (upper and lower), what must be concluded?

The process appears non-random and should be checked.

Which of the following exemplify a capable process?

The range of process variability is much less than the width of customer specifications.

In a p-chart, as the sample size increases, how does the standard deviation of the sampling distribution for the proportion of defective items change?

The standard deviation decreases.

Comparing a theoretical sampling distribution to the process distribution, which of the following is true?

The variability of the sampling distribution is less than that of the process distribution.

When comparing a sampling to a process distribution, what are the most important things to note?

They have the same means, are normally distributed, and sampling has less variability.

Why do statistical process control analysts perform run tests, even when control charts demonstrate all points within the limits?

To determine whether patterns can be detected.

True or false: In acceptance sampling, a type of quality control inspection, 100% of product in a given lot are checked for conformanc

false

true or false: In order to create new samples, the runs are transformed into a series of Us and Ds and into a series of As and Bs.

false

There is too much inspection when the cost of inspection is __________ the cost of passing defectives

greater than

The decision about where to use control charts should focus on aspects of the process that

have a tendency to go out of control, and affect product or service characteristics

Given a stable process, we must ask the question whether the ______ of process output is within an acceptable range

inherent variability

Given a stable process, we must ask the question whether the ______ of process output is within an acceptable range.

inherent variability

the implication for Taguchi is that reducing the variation inherent in a process will result

lowering the cost of poor quality lowering the loss to society

What are the two different types of run tests?

median and up/down

select the best definition of process variability.

natural or inherent variability in a process

Even a process that is functioning as it should will not yield output that conforms exactly to a standard. Why not?

natural variation

For practical reasons, the c-chart uses which probability distribution as an approximation to the Poisson?

normal

For attribute data a c-chart is used to monitor _____

number of defects per unit

statistical process control is

quality control efforts that occur during production

When computing the control limits for the p-chart, what value is used when the population proportion of defective items is not known?

sample proportion of defective items

Six Sigma refers to achieving a process variability so small that the design specifications represent ___ standard deviations above and below the process mean

six

Select the best definition of assignable variation.

special, non random

How do Specifications differ from Control Limits?

specifications refer to the entire process and control limits are set on the sampling distribution.

Random variation in a process indicates __________; whereas non-random variation indicates process __________.

stability/instability

A range control chart is used to check

the dispersion

Select the best definition of process capability.

the inherent variability of process output relative to the variation allowed by the design specifications

For attribute data a p-chart is used to monitor

the proportion of defective items generated by a process

We do not use the process standard deviation in a range control chart, because __

the underlying sampling distribution is not normal

Select the best definition of capability analysis.

to determine whether the variability of a stable process falls within tolerances

In the control process, only those characteristics that can be counted or measured are candidates for control.

true

True or false: Sometimes non-random variation can indicate excellent quality.

true

all processes have variation

true