Ishikawa
Diagram
The
Ishikawa Diagram, also known as the
Fishbone Diagram or
the Cause-and-Effect
Diagram,
is a tool used for systematically identifying and presenting all the
possible causes of a particular problem
in graphical format. The possible causes are presented at various
levels of detail in connected branches, with the level of detail
increasing as the branch goes outward, i.e., an outer branch is a cause
of the inner branch it is attached to. Thus, the outermost
branches usually indicate the root causes of the problem.
The Ishikawa
Diagram resembles a
fishbone
(hence the
alternative name "Fishbone Diagram") - it has a box (the 'fish head')
that contains the statement of the problem at one end of the diagram.
From this box originates the main branch (the 'fish spine') of the
diagram. Sticking out of this main branch are major branches that
categorize the causes according to their nature.
In
semiconductor manufacturing, 4 major branches are often used by
beginners, referred to as the
'4 M's', corresponding to 'Man',
'Machine', 'Materials', and 'Methods'. Sometimes 5 branches are used
('5 M's'), with the fifth branch standing for 'Measurement', or even
'M-vironment.' These 'M's' or problem cause categories are
used to classify each cause identified for easier analysis of data. Of course, one is not
constrained to use these categories in a fishbone diagram.
Experienced users of the diagram add more branches and/or use different categories, depending
on what would be more effective in dealing with the problem. Figure 1
shows the
basic
framework
of an Ishikawa Diagram.
Figure 1.
The Basic '4 M's' Framework of an Ishikawa Diagram
The Ishikawa Diagram is
employed by a problem-solving team as a tool for
collating
all
inputs (as to what are the causes of the problem they're addressing) systematically and graphically,
with the inputs usually coming from a brainstorming session. It
enables the team to
focus
on
why
the problem occurs, and not on the history or symptoms of the problem,
or other topics that digress from the intent of the session. It also
displays a real-time
'snap-shot'
of the
collective inputs of the team as it is updated.
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See Also:
Pareto
Chart;
Brainstorming
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