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Exam 15: Statistical Quality Control

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Question 1

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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.

F) A) and B)
G) None of the above

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Question 2

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Given the following process control data for a quality attribute (three samples of size 400 each): If the process is known to produce 11 percent defectives on average,what are the upper and lower control limits for an alpha risk of .10? .05? .01?

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.1357 and ...

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Question 3

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Four samples of three observations each have been taken,with actual measurements (in centimetres)shown below.Construct three sigma mean and range charts,and determine if corrective action is needed. 11eab92b_c48d_2c65_99e6_039f93955d70

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

A Quality Analyst wants to construct a control chart for determining whether three machines,all producing the same product,are under control with regard to a particular quality variable.Accordingly,he sampled four units of output from each machine,with the following results: Using the factors for three sigma control limits,what are the x-bar chart upper and lower control limits?

Studies on a machine that molds plastic water pipe indicate that when it is injecting 25 mm diameter pipe,the process standard deviation is 0.50 mm.The 25 mm pipe has a specification of 25 mm plus or minus 1.0 mm.What is the process capability index (Cp) ?

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

Given the following process control data for a quality attribute (three samples of size 400 each): If the process is known to produce 11 percent defectives on average,what is the alpha risk (probability of Type I error)for upper and lower control limits of .1256 and .0944 respectively? .1412 and .0788? .1568 and .0632?

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

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

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

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?

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

Given the following process control data for a normally distributed quality variable (three samples of size four each): If the process is known to have a mean of 15 and a standard deviation of 3,what are the three sigma upper and lower control limits for an x-bar chart?

Using three sigma control limits (rather than two sigma limits) tends to have what impact on error probabilities?

The range chart (R-chart) is most likely to detect a change in:

Design specifications are equivalent to control limits.

Control limits and process variability are directly related.

Given the following process control data for a quality attribute (three samples of size 400 each): What is the sample proportion of defectives for sample #1? #2? #3?

The term "2 sigma limits" in the context of a control chart refers to the variability of the: