Chapter 2
Basic Tools for
Improving Quality
7 Basic Tools by Ishikawa
•
•
•
•
•
•
•
Histogram
Pareto chart
Scatter plot
Control chart
Cheek sheet
Cause-and-effect diagram
Defect concentration diagram
2.1 Histogram
Table 2.1 Example Data
24
31
81
27
42
51
58
82
21
54
53
60
32
83
55
64
33
51
41
58
45
70
57
25
50
51
66
55
32
23
64
58
52
84
56
52
33
43
45
58
36
85
68
37
53
40
54
55
49
50
74
52
40
35
41
28
56
72
61
63
59
62
60
56
39
34
46
75
69
68
30
61
59
76
59
76
51
73
42
52
48
87
78
65
57
63
43
66
79
64
65
44
49
67
47
71
69
45
46
62
Histogram by Minitab
Histogram by Excel
Histogram
Frequency
6
11
18
29
20
10
6
0
35
30
25
Frequency
Bin
29
39
49
59
69
79
89
More
20
15
10
5
0
29
39
49
59
69
Bin
79
89
More
2.2 Pareto Charts
• A Pareto chart is a bar graph that shows the
relative frequencies of observations in a
descending order.
– draws its name from an Italian economist, Vilfredo
Pareto (1848–1923)
– J. M. Juran is credited with being the first person to
apply it to industrial problems
Table 2.3 Nonconformities and
Associated Monetary Losses
Lot #
Date
NI
Scratches
ML
2014
2026
2013
2032
2030
2028
2040
2011
2010
2015
2022
2021
2024
2023
2018
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Totals
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
15,000
22
23
30
18
20
21
19
12
14
16
12
13
21
22
19
282
$86
88
100
79
81
83
80
66
69
74
66
68
83
86
80
1189
Broken
Tips
36
39
41
37
28
39
33
29
31
30
22
27
35
29
23
479
ML
Spots
ML
Others
ML
$160
170
178
164
146
170
152
150
149
148
136
145
158
150
138
2314
6
3
8
14
15
10
9
5
8
7
4
11
13
10
6
129
$20
10
24
35
38
28
25
18
24
22
16
27
31
26
20
364
3
2
4
5
3
6
2
7
6
9
5
2
1
6
7
68
$6
3
7
9
6
10
3
12
10
16
9
3
1
10
12
117
Pareto Chart on Nonconformities
Pareto Chart on Monetary Losses
2.3 Scatter Plots
• A scatter plot is another simple graphical device
• The simplest type is a bivariate scatter plot, in
which two quantities are plotted.
• Scaling of the two axes is somewhat arbitrary
• A time sequence plot is a type of scatter plot in
that data on one variable are plotted against a
second variable, time.
• A probability plot is another type of scatter plot.
Table 2.4 Data for Quality
Improvement Program
Month
January
February
March
April
May
June
July
August
September
October
November
December
No. of Employees Cost of Training
Trained (000)
(000)
12
23
10
19
10
27
11
20
9
15
6
10
8
14
5
8
6
9
3
5
2
3
2
4
Table 2.4 Data for Quality
Improvement Program
Variations of Scatter Plots
• Use number or special symbols for duplicated data
points.
• Use “range frames”, instead of scales
2.4 Control Charts
• A control chart is a time sequence plot with
“decision lines” added.
• These decision lines are used to try to determine
whether or not a process is in control.
– Type I and II errors
Typical Control Chart
-3s
Upper
control
limit
-2s
1s
-1s
3s
1
2
3
4
5
6
Sample number
7
8
9
10
95%
2s
2s
Lower
control
limit
99.73%
1s
=0 1s
Central
Line
2s
2.5 Check Sheet
• A check sheet is a means of recording historical
data on causes of nonconformities or
nonconforming units.
– The general idea is to record all pertinent information
relative to nonconformities and nonconforming units, so
that the sheets can facilitate process improvement.
– Such information might include notes on raw materials,
machine performance, or operator changes.
2.6 Cause-and-Effect Diagram
• The cause-and-effect diagram was introduced in
Japan in 1943 by Professor Kaoru Ishikawa of the
University of Tokyo.
– For that reason it is sometimes called an Ishikawa
diagram; it has also been called a fishbone chart.
Cause-and-Effect Diagram
2.7 Defect Concentration Diagram
• It is simply a schematic diagram that shows the
various sides of a unit of production, with the
positions where nonconformities occur pinpointed.
Defect Concentration Diagram
2.8 The 7 Newer Tools
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Affinity Diagram
Interrelationship Digraph
Tree Diagram
Prioritization Matrix
Matrix Diagram
Process Decision Program Chart
Activity Network Diagram
2.8.1 Affinity Diagram
• An affinity diagram is a set of ideas about a particular topic
that are grouped into clusters.
• The diagram is the end product of brainstorming that is
performed in a prescribed manner.
2.8.1 Affinity Diagram
2.8.2 Interrelationship Digraph
• An interrelationship digraph is used for identifying and
exploring causal relationships between related ideas.
• This is a step beyond an affinity diagram, as an
interrelationship digraph is a figure with arrows indicating
relationships between ideas.
2.8.2 Interrelationship Digraph
2.8.3 Tree Diagram
• A tree diagram is somewhat similar to a cause-and-effect
diagram in that a desired effect (e.g., reducing delivery
delays) can be shown pictorially as related to the factors
that can lead to the effect.
• A tree diagram will generally more closely resemble a
company organizational chart in appearance than a causeand-effect diagram.
• A tree diagram is a more structured display than either an
affinity diagram or an interrelationship digraph.
2.8.3 Tree Diagram
2.8.4 Prioritization Matrix
• A prioritization matrix is a relative ranking of issues jobs,
objectives, products, and so on.
• The ranking is accomplished by comparing the components
pairwise so that a logical and consistent ranking results.
2.8.4 Prioritization Matrix
2.8.5 Matrix Diagram
• A matrix diagram is used for showing relationships between
two or more sets of ideas, projects, and so on.
• The matrix can have one of several different forms.
• At least five forms have been used:
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–
–
–
–
C-shaped
L-shaped
T-shaped
X-shaped, and
Y-shaped
2.8.5 Matrix Diagram
2.8.6 Process Decision Program
Chart
• A process decision program chart is a listing of undesirable
events and corresponding contingency actions relative to
planned actions.
• It is used when there is considerable concern about the
possibility of negative unanticipated outcomes.
2.8.6 Process Decision Program
Chart
2.8.7 Activity Network Diagram
• This is essentially a combination of two well-known
techniques: PERT (Program Evaluation and Review) and
CPM (Critical Path Method).
2.8.7 Activity Network Diagram