Exam 14: Quality Control

The probability of concluding that assignable variation exists when only random variation is present is: (I) the probability of a Type I error. (II) known as the alpha risk. (III) highly unlikely. (IV) the sum of probabilities in the two tails of the normal distribution.

The chair of the operations management department at Quality University wants to construct a p-chart for determining whether the four faculty teaching the basic P/OM course are in control with regard to the number of students who fail the course. Accordingly, he sampled 100 final grades from last year for each instructor, with the following results: Instructor Number of Failures Prof. A 13 Prof. B 0 Prof. C 11 Prof. D 16 Using .95 control limits (5 percent risk of Type I error), which instructor(s), if any, should he conclude is (are) out of control?

Which of the following relationships must always be incorrect?

The amount of inspection needed depends on __________ and __________.

A quality analyst wants to construct a control chart for determining whether four machines, all producing the same product, are in control with regard to a particular quality attribute. Accordingly, she inspected 1,000 units of output from each machine in random samples, with the following results: Machine Total Defectives \#1 23 \#2 15 \#3 29 \#4 13 What is the estimate of the standard deviation of the sampling distribution of sample proportions for this process?

A control chart used to monitor the process mean is the:

The specification limits for a product are 8 cm and 10 cm. A process that produces the product has a mean of 9.5 cm and a standard deviation of 0.2 cm. What is the process capability, Cpk?

A run test checks a sequence of observations for randomness.

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.

Which of the following quality control sample statistics indicates a quality characteristic that is an attribute?

Patterns of data on a control chart suggest that the process may have nonrandom variation.

Range charts are used mainly with attribute data.

Attribute data are counted, variable data are measured.

The best way to assure quality is to use extensive inspection and control charts.

A design engineer wants to construct a sample mean chart for controlling the service life of a halogen headlamp his company produces. He knows from numerous previous samples that this service life is normally distributed with a mean of 500 hours and a standard deviation of 20 hours. On three recent production batches, he tested service life on random samples of four headlamps, with these results: Sample Service Life (hours) 1 495 500 505 500 2 525 515 505 515 3 470 480 460 470 What is the standard deviation of the sampling distribution of sample means for whenever service life is in control?

Studies on a machine that molds plastic water pipe indicate that when it is injecting 1-inch-diameter pipe, the process standard deviation is 0.05 inches. The 1-inch pipe has a specification of 1 inch plus or minus 0.10 inch. What is the process capability index (Cpk) if the long-run process mean is 1 inch?

Approving the effort that occurs during the production process is known as acceptance sampling.

Larger samples will require wider x-bar control limits because there is more data.

A quality analyst wants to construct a control chart for determining whether four machines, all producing the same product, are in control with regard to a particular quality attribute. Accordingly, she inspected 1,000 units of output from each machine in random samples, with the following results: Machine Total Defectives \#1 23 \#2 15 \#3 29 \#4 13 What is the sample proportion of defectives for machine #1?

A control chart used to monitor the fraction of defectives generated by a process is the: