CH 10: Statistical Quality Control

Question 1

Statistical Quality Control

Answer 1

uses statistical techniques and sampling to monitor and test the quality of goods and services

Question 2

Acceptance Sampling

Answer 2

part of statistical quality control that relies primarily on inspection of previously provided service or produced items

Question 3

Statistical Process Control

Answer 3

part of statistical quality control that occurs during production

Question 4

Inspection

Answer 4

appraisal activity that compares quality of good or service standard

Question 5

When can inspection occur?

Answer 5

before, during, or after production

Question 6

what does inspection before production make sure?

Answer 6

that inputs are acceptable

Question 7

what does inspection during production make sure?

Answer 7

conversion of inputs into outputs is proceeding in an acceptable manner

Question 8

what is inspection after production?

Answer 8

final verification of conformance before passing goods on to customers

Question 9

what planning steps do effective statistical process controls require?

Answer 9

1. define the important quality characteristics, and how each is measured
2. for each characteristic: determine quality control point; plan how inspection is to be done, how much to inspect, how often to inspect, and whether off-site or on-site inspection is required; plan corrective action

Question 10

defining the quality characteristics

Answer 10

• define in sufficient detail, what is to be controlled
• different characteristics may require different approaches for control purposes
• only those that can be measured are candidates for control
• it is important to consider how measurement will be accomplished
• there must be a standard that can be used to evaluate

Question 11

determining quality control point

Answer 11

• important to restrict inspection efforts to the points where they can do the most good (adds to the cost of product)

Question 12

inspection points in manufacturing

Answer 12

• at beginning of process
• at end of process
• before a costly operation
• before an irreversible process
• before a covering process

Question 13

inspection points in service

Answer 13

• incoming purchased materials and supplies
• personnel
• service interfaces
• outgoing completed work

Question 14

how is inspection to be done

Answer 14

usually technical and varies depending on the characteristics of the product or service that needs to be controlled

Question 15

how much to inspect

Answer 15

range from no inspection at all or inspect each unit

Question 16

how often to inspect

Answer 16

low cost, high volume products require very little inspection

items that have large costs associated with passing defective products often require more intensive inspection

Question 17

centralized inspection

Answer 17

specialized equipment and more favourable test environment

Question 18

on-site inspection

Answer 18

allow quicker decisions to be made and avoiding introducing extraneous factors

Question 19

statistical process control (SPC)

Answer 19

concerned with statistical evaluation of the product in the production process

Question 20

random variation

Answer 20

natural or inherent process variation in process output

• due to combined influences of countless minor factors
• amount of inherent variability differs from process to process
• no corrective action is required when the only source of variation in output is random

Question 21

assignable variation

Answer 21

variability in process that is no random

• main source of assignable variation can usually be identified and eliminated through corrective action

Question 22

sample statistics

Answer 22

used to judge randomness of process variations

Question 23

what is the variability of a sample statistic described by

Answer 23

its sampling distribution

Question 24

central limit theorem

Answer 24

as the sample size increases, distribution of sample averages approaches a normal distribution regardless of shape of the sampled population

Question 25

control process

Answer 25

1. define: in sufficient detail what is to be controlled
2. measure: only characteristics that can be counted or measured
3. compare: must be a standard of competition that can be used to evaluate the measurements
4. evaluate: established definition of out of control
5. correct: process that is judged to be out of control
6. monitor: results to ensure corrective action is effective

Question 26

control charts definition

Answer 26

time-ordered plot of sample statistics, with limits and used to distinguish between random and assignable variation

Question 27

what do control charts do

Answer 27

• monitor output to see if it is random

Question 28

what is a necessary condition for a process to be deemed in control

Answer 28

all data points must fall in between upper and lower control limits

Question 29

control limits

Answer 29

define the range of acceptable variation for the sample statistic (upper and lower limit)

Question 30

what does a sample statistic that falls between the two limits suggest

Answer 30

random variation

Question 31

what does a sample statistic that falls outside the two limits suggest

Answer 31

assignable variation

Question 32

type I error

Answer 32

concluding that the process has shifted when in reality it has not

= alpha (significance level)

Question 33

type II error

Answer 33

concluding the process has not shifted when in reality is has

Question 34

variable data

Answer 34

measured, usually on a continuous scale

Question 35

attribute data

Answer 35

counted

Question 36

sample mean control charts

Answer 36

used to monitor the process mean

Question 37

sample range control charts

Answer 37

used to monitor process dispersion or spread

Question 38

p-chart

Answer 38

control charts for the sample proportion of defectives, and is used to monitor the proportion of defective items generated by the process

Question 39

c-chart

Answer 39

control chart for the sample number of defects per unit

Question 40

managerial considerations concerning control charts

Answer 40

1. at what point in the process to use control charts
2. what size samples to take
3. what type of control chart to use
4. how often samples should be taken

Question 41

run test

Answer 41

check for patterns in a sequence of observations

Question 42

what does a run test enable

Answer 42

better job of detecting abnormalities in a process and provides insights correcting a process that is out of control

Question 43

run

Answer 43

sequence of observations with a certain characteristic, followed by one or more observations with a different characteristic

Question 44

how are control charts and run tests used

Answer 44

ideally, both together to analyze process output, along with a plot of the data

Question 45

procedure of using a control chart and run test

Answer 45

1. compute control limits for the process output
2. conduct median and up/down run tests

Question 46

design specification

Answer 46

established by engineering design or customer requirements, is a range of values in which individual units of output must fall in order to be acceptable

Question 47

process variability

Answer 47

reflects the natural or inherent variability in a process

Question 48

process capability

Answer 48

ability of a process to meet the design specification

Question 49

capability analysis

Answer 49

performed on a process that is in control for the purpose of determining if the range of variation is within design specification that would make the output acceptable for its intended use

Question 50

process capability ratio

Answer 50

ratio of the design specification width to the process width