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Overview: Also known as the Fish
Bone Analysis or the Ishikawa Diagram after its inventor. The popular name of “Fish Bone Analysis” comes
from its similarity in appearance to a set of fish bones.
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This analysis provides a structured way of examining
the various possible causes of any result. The procedures starts
with the result, or the effect, being at the “head” position
of the fish bone and the spine form the major categories of causes.
The individual categories are then broken down to specific causes.
Cause
categories can be almost anything that can have an impact on
the result. Popular choices in “problem solving” are:
Men / Machine / Methods / Materials. In many instances, “Acts
of God / Mother Nature” are also included. It is also possible
to use the 5S categories
of Sort / Set / Shine / Standardise / Sustain. |
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Origins:
The Cause - Effect Analysis was developed by Dr Kaoru Ishikawa of Japan.
Dr Ishikawa advocated that all employees should be trained in the
use of seven quality control tools including Pareto charts; Cause
and Effect diagrams; Histograms; and Scatter diagrams.
Using the Cause - Effect Analysis:
The Cause - Effect Analysis is an easy tool to use as well as being
a very effective tool in exploring the causes of any observation.
However, there are certain points to pay particular attention to:
- when generating the potential causes - remember that
it is causes that matter not symptoms;
- once all the potential causes have been generated,
group them by category;
- assess each category and eliminate duplications;
- once the individual “spines” (cause categories) and “bones” (individual
causes) are in place, then analyse each cause to make sure it is
discrete and unique event, otherwise, these are further broken down
into various
sub-causes.
Once the analysis is complete, the team can then “vote” on
the most likely cause by giving everyone a fixed number of “votes” to
allocate between the various causes. While this allows the team
to focus on what everyone considers the most likely cause rapidly,
it does not mean the other causes are invalid.
Practical
tip: Use self-adhesive notes to write down the Individual
Causes - they can be moved easily between the different Cause Categories.
Mental
block: The “Fish Bone” does not have
to be symmetrical - too many teams spend too long contriving categories
to make sure that there are the same number of categories on each
side. It’s only a diagram! |
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Additional Resources:
Background
to Kaoru Ishikawa
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Sigma take on Cause-Effect Analysis
Ishikawa, K., "Guide to Quality Control", Asian Productivity
Organization, 1986
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