Deck 14: Statistical Methods for Quality Control

Question 1

A control chart that is used when the output of a production process is measured in terms of the proportion defective is

A)a p chart
B)an x-bar chart
C)an R chart
D)an np chart

Answer 1

a p chart

Question 2

Normal or natural variation in the quality of production output that is due purely to chance is called

A)common-cause variation
B)assignable-cause variation
C)control-cause variation
D)correctable-cause variation

Answer 2

common-cause variation

Question 3

The sample result plotted on an np control chart is

A)n_p
B)np
C)the number of perfect units in the sample
D)the number of defective units in the sample

Answer 3

the number of defective units in the sample

Question 4

A control chart that is used to monitor the range of the measurements in a sample is

A)a p chart
B)an x-bar chart
C)an R chart
D)an np chart

Question 5

Quality assurance consists of

A)quality control
B)quality engineering
C)quality assurance
D)Both quality control and quality engineering are correct.

Question 6

A control chart used when the output of a process is measured in terms of the mean value of a variable such as a length, weight, temperature, and so on is

A)a p chart
B)an x-bar chart
C)an R chart
D)an np chart

Question 7

Variation in the quality of production output that is due to factors such as machine tools wearing out is called

A)common-cause variation
B)assignable-cause variation
C)acceptable-cause variation
D)natural-cause variation

Question 8

A control chart that is used to monitor the number of defectives in a sample is

A)a p chart
B)an x-bar chart
C)an R chart
D)an np chart

Question 9

If the value of c in a single-stage acceptance sampling plan is increased, with n remaining constant, the probability of accepting the lot

A)increases
B)decreases
C)remains the same
D)might increase or decrease, depending on the percent defective in the lot

Question 10

The entire system of policies, procedures, and guidelines established by an organization to achieve and maintain quality is called

A)quality control
B)quality engineering
C)quality assurance
D)Both quality control and quality engineering are correct.

Question 11

An operating characteristic curve is based on a ________ probability distribution.

A)normal
B)exponential
C)binomial
D)uniform

Question 12

Control charts that are based on data indicating the presence of a defect or the number of defects are called ______ control charts.

A)attributes
B)variables
C)common-cause
D)assignable-cause

Question 13

Which of the following is not a type of a control chart?

A)a p chart
B)an x-bar chart
C)an R chart
D)All of these are types of control charts.

Question 14

__________ consist(s) of making a series of inspections and measurements to determine whether quality standards are being met.

A)Quality control
B)Quality engineering
C)Quality assurance
D)Both quality control and quality engineering are correct.

Question 15

The control limits for a p chart are how many standard deviations above and below the proportion defective?

A)one
B)two
C)three
D)four

Question 16

The control limits for an x-bar chart are how many standard deviations above and below the process mean?

A)one
B)two
C)three
D)four

Question 17

The general practice in quality control is to set the control chart's upper and lower control limit values equal to the variable's mean value +/-

A)1 standard deviation
B)2 standard deviations
C)2.5 standard deviations
D)3 standard deviations

Question 18

A graphical tool used to help determine whether a process is in control or out of control is a

A)scatter diagram
B)histogram
C)control chart
D)None of the other answers is correct.

Question 19

Which of the following is a statistical method used in quality control?

A)statistical process control
B)acceptance sampling
C)Both statistical process control and acceptance sampling are correct.
D)None of the other answers is correct.

Question 20

If the calculated lower-control limit of a p chart is negative,

A)a mistake has been made in the calculations
B)use the absolute value of the lower limit
C)it is set to zero
D)None of the other answers is correct.

Question 21

In contrast to Deming's philosophy, which required a major cultural change in the organization, Juran's programs were designed to improve quality by

A)working within the current organizational system
B)reducing the number of levels in the organizational structure
C)changing customer perception and expectations
D)identifying and replacing the most counter-productive employees

Question 22

Rejecting a poor-quality lot would be a

A)Type I error
B)Type II error
C)correct decision
D)None of the other answers is correct.

Question 23

In acceptance sampling, the risk of rejecting a good quality lot is known as

A)consumer's risk
B)producer's risk
C)a Type II error
D)None of the other answers is correct

Question 24

DFSS stands for

A)Defects Found Sifting and Sorting
B)Design For Six Sigma
C)Deviation From Specifications and Standards
D)Defer For Statistical Study

Question 25

The control limits for an np chart are how many standard deviations above and below the expected number of defectives?

A)one
B)two
C)three
D)four

Question 26

When a Motorola executive said "That evaluation is …. perhaps the most cost-effective, value-added business consultation available anywhere in the world today" he was referring to

A)ISO 9000 standards
B)the Six Sigma philosophy
C)Deming's 14 Points
D)the Malcolm Baldrige Quality Award

Question 27

Consumer's risk is

A)the same concept as the producer's risk
B)a Type II error
C)a Type I error
D)None of the other answers is correct.

Question 28

A graph showing the probability of accepting the lot as a function of the percent defective in the lot is

A)a power curve
B)a control chart
C)an operating characteristic curve
D)None of the other answers is correct.

Question 29

A form of acceptance sampling in which more than one sample or stage is used is called a

A)single-sample plan
B)multiple-sampling plan
C)multinomial sampling plan
D)None of the other answers is correct.

Question 30

The maximum number of defective items that can be found in the sample and still lead to acceptance of the lot is

A)the upper control limit
B)the lower control limit
C)the acceptance criterion
D)None of the other answers is correct.

Question 31

A group of items such as incoming shipments of raw material is called

A)a sample plan
B)an incoming control
C)a lot
D)None of the other answers is correct.

Question 32

Accepting a good-quality lot would be a

A)Type I error
B)Type II error
C)correct decision
D)None of the other answers is correct.

Question 33

In acceptance sampling, the risk of accepting a poor quality lot is known as

A)consumer's risk
B)producer's risk
C)a Type I error
D)None of the other answers is correct.

Question 34

Juran proposed a simple definition of quality:

A)customer satisfaction
B)conformance to specifications
C)fitness for use
D)commitment to excellence

Question 35

Six Sigma represents a quality level of at most ____ defects per million opportunities.

A)3.4
B)6.0
C)19.7
D)99.5

Question 36

The Malcolm Baldrige National Quality Award was established in

A)1954
B)1971
C)1987
D)1993

Question 37

A statistical procedure in which the number of defective items found in a sample is used to determine whether a lot should be accepted or rejected is called

A)statistical process control
B)acceptance sampling
C)quality assurance
D)control charts

Question 38

Producer's risk is

A)the same as the consumer's risk
B)a Type II error
C)a Type I error
D)None of the other answers is correct.

Question 39

The second stage of a two-stage acceptance sampling plan is executed when the first-stage result is

A)x₁ > c₁
B)c₁ < x₁ < c₂
C)x₁ > c₂
D)x₁ > c₁ + c₂

Question 40

The three quality processes on which Juran's approach to quality focused include all of the following except

A)quality planning
B)quality execution
C)quality control
D)quality improvement

Question 41

A production process that is in control has a mean ( $\mu$ ) of 80 and a standard deviation ( $\sigma$ ) of 10.
a.Determine the upper and the lower control limits for sample sizes of 25.
b.Five samples had means of 81, 84, 75, 83, and 79. Construct an x-bar chart and explain whether or not the process is in control.

Question 42

The two general classifications of attributes in quality control are

A)random and predictable
B)controllable and uncontrollable
C)variable and constant
D)defective and nondefective

Question 43

The following data represent the filling weights based on samples of 14.5 ounce cans of whole peeled tomatoes. Ten samples of size 5 were taken. Use Excel to develop an x-bar chart.

Question 44

Process control and acceptance sampling procedures are most closely related to

A)linear regression procedures
B)interval estimation procedures
C)hypothesis testing procedures
D)analysis of variance procedures

Question 45

A production process is considered in control if 4% of the items produced are defective. Samples of size 100 are used for the inspection process.
a.Determine the standard error of the proportion.
b.Determine the upper and the lower control limits for the p chart.

Question 46

In practice, it is common to use the sample _____ to estimate the process _________.

A)variances, range
B)means, variance
C)standard deviations, mean
D)ranges, standard deviation

Question 47

Brakes Shop, Inc., is a franchise that specializes in repairing brake systems of automobiles. The company purchases brake shoes from a national supplier. Currently, lots of 1,000 brake shoes are purchased, and each shoe is inspected before being installed on an automobile. The company has decided, instead of 100% inspection, to adopt an acceptance sampling plan.
a.Explain what is meant by the acceptance sampling plan.
b.If the company decides to adopt an acceptance sampling plan, what kinds of risks are there?
c.The quality control department of the company has decided to select a sample of 10 shoes and inspect them for defects. Furthermore, it has been decided that if the sample contains no defective parts, the entire lot will be accepted. If there are 50 defective shoes in a shipment, what is the probability that the entire lot will be accepted?
d.What is the probability of accepting the lot if there are 100 defective units in the lot?

Question 48

The upper and lower control limits of a process are 66 and 54. Samples of size 16 are used for the inspection process. Determine the mean and the standard deviation for this process.

Question 49

A soft drink filling machine is set up to fill bottles with 12 ounces of soft drink. The standard deviation s is known to be 0.4 ounces. The quality control department periodically selects samples of 16 bottles and measures their contents. Assume the distribution of filling volumes is normal.
a.Determine the upper and lower control limits and explain what they indicate.
b.The means of six samples were 11.8, 12.2, 11.9, 11.9, 12.1, and 11.8 ounces. Construct an x-bar chart and indicate whether or not the process is in control.

Question 50

The quality control department of a company has decided to select a sample of 20 items from each shipment of goods it receives and inspect them for defects. It has been decided that if the sample contains no defective parts, the entire lot will be accepted. Each shipment contains 1,000 items.
a.What is the probability of accepting a lot that contains 10% defective items?
b.What is the probability of accepting a lot that contains 5% defective items?
c.What is the probability of rejecting a lot that contains 15% defective items?

Question 51

The following data represent the filling weights based on samples of 14.5 ounce cans of whole peeled tomatoes. Ten samples of size 5 were taken. Use Excel to develop an R chart.

Question 52

We can examine the effect of the sampling plan on both types of risks by varying the assumed

A)percentage of defective items in the lot
B)number of defective items in the sample
C)probability of accepting the lot
D)number of units in the lot

Question 53

If the value of c in a single-stage sampling plan is increased, with n remaining constant, the probability of accepting the lot

A)increases
B)decreases
C)is unchanged
D)might increase or decrease, depending on the lot percent defective

Question 54

Heavy emphasis on statistical analysis and careful measurement are closely associated with

A)Total Quality
B)ISO 9000
C)Baldrige National Quality Program
D)Six Sigma

Question 55

A production process is considered in control if 6% of the items produced are defective. Samples of size 300 are used for the inspection process.
a.Determine the standard error of the proportion.
b.Determine the upper and the lower control limits for the p chart.

Question 56

Control charts based on data that can be measured on a continuous scale are called

A)normal control charts
B)variables control charts
C)attributes control charts
D)precision control charts

Question 57

The process mean and standard deviation can be estimated by using samples that are selected from the process when

A)it has only assignable-cause variation
B)its output is uniformly distributed
C)it is assumed to be operating in control
D)it is operating at peak capacity

Question 58

The following data represent the filling weights based on samples of 350-gram containers. Ten samples of size 5 were taken. Use Excel to develop an R chart.

Question 59

An acceptance sampling plan uses a sample of 18 with an acceptance criterion of zero. Determine the probability of accepting shipments that contain 5, 10, 15, 20, 25, 30, 35, 40, and 45% defective units.

Question 60

The following data represent the filling weights based on samples of 350-gram containers. Ten samples of size 5 were taken. Use Excel to develop an x-bar chart.

Question 61

Harry Coates wants to construct and R charts at the bag-filling operation for Meow Chow cat food. He knows that when the filling operation is functioning correctly, bags of cat food should average 50.00 pounds and 5-bag samples should have an average range of .330 pounds.
Harry had twenty 5-bag samples taken at 2-hour intervals and the sample means and ranges are shown below. Determine the center lines and upper and lower control limits for the and R charts.

Question 62

To inspect incoming shipments of components, a manufacturer is considering samples of sizes 12, 15, and 18. Use binomial probabilities to select a sampling plan that provides a producer's risk of $\alpha$ = .12 when p₀ is .04 and a consumer's risk of $\beta$ = .08 when p₁ is .25.

Question 63

Janie Hochevar, director of production at the center, has decided to record the number of defective labels in random daily samples on control charts. Janie estimates that 1.5 percent loose labels is typical when the labeling process is in control.
Twelve daily samples, each consisting of 200 pairs of jeans, were selected and examined. The number of defective labels found in each sample is shown below.

a. Determine the center line and the 3s control limits for the p chart.
b. Decide if the labeling operation is in control.

Question 64

The weight of bags of cement filled by Granite Rock Company's packaging process is normally distributed with a mean of 50 pounds and a standard deviation of 1.5 pounds when the process is in control. What should the control limits be for a sample mean, , chart if 9 bags are sampled at a time?

Question 65

A process that is in control has a mean of $\mu$ = 56.5 and a standard deviation of $\sigma$ = 3.4. What should the control limits be for a sample mean chart if samples of size 8 are taken?

Question 66

The No-Cal Bottling Company bottles soft drinks for sale to government commissaries. The bottles come in only one flavor (chocolate-lemon) and only one size (32 ounces). Joan Stickler, the quality control officer for the commissaries, wants to keep track of the fill weights of No-Cal and begins to draw daily samples of 100 bottles from the daily receipts. The first ten sample means and ranges are:
If sample ranges ordinarily average 2.5 ounces:
a. Compute 3s control limits for sample means.
b. Compute 3s control limits for sample ranges.
c. What would you conclude about the fill weights of NoCal?

Question 67

An acceptance sampling plan with n = 20 and c = 1 has been designed with a producer's risk of .12.
a. Was the value of p₀ equal to .02, .03, .04, or .05?
b. What is the consumer's risk associated with this plan if p₁ is .08?
c. Assume the consumer's risk found in (b) is unacceptably high. Which modification of the sampling plan will result in the greater reduction of the consumer's risk, increasing n to 30 or decreasing c to 0?

Question 68

Ledd Electronics has received a large shipment of power supply units for the desktop computers being assembled. The units are coming from a new supplier and Ledd is not sure what the actual defect rate will be for this component. Ledd is considering an acceptance sampling plan with n = 30 and c = 1.
a. Find the probability of accepting a lot when the defect rate is 2%, 4%, and 6%.
b. What happens to the producer's risk as the defect rate increases?
c. What happens to the consumer's risk as the defect rate increases?

Question 69

The quality control department of a company has decided to select a sample of 10 items from the shipments received; and if the sample contains no defective parts, the entire shipment will be accepted.
a.If there are 40 defective items in a shipment, what is the probability that the entire lot will be accepted?
b.Use the binomial table and read the probability of accepting lots that contain 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50% defective units.

Question 70

A U.S. manufacturer of digital video recorders purchases a circuit board from a Taiwanese firm. The circuit boards are shipped in lots of 2000. The acceptance sampling procedure uses 12 randomly selected circuit boards. The acceptance number is 1. If p₀ is .03 and p₁ is .20, what are the producer's and consumer's risks for this plan?

Question 71

Snipper, Inc. manufactures lawnmowers that require minor, final assembly by the customer. A sealed plastic bag containing the hardware (nuts, bolts, washers, and so on) needed for final assembly is included with each lawnmower shipped. During a week of normal, in-control operation, twenty samples of 200 bags of hardware were examined for content (hardware type and count) accuracy. A total of 104 bags of the 4000 examined failed to have the correct contents.
a. Compute the upper limit, center line, and lower limit for a p chart.
b. Compute the upper limit, center line, and lower limit for an np chart.

Question 72

A process sampled 30 times with a sample of size nine resulted in = 12.7 and = 0.8. Compute the upper and lower control limits for the and charts for this process.