|One of the Seven Basic Tools of Quality|
|First described by||Kaoru Ishikawa|
|Purpose||To break down (in successive layers of detail) root causes that potentially contribute to a particular effect|
Ishikawa diagrams (also called fishbone diagrams, herringbone diagrams, cause-and-effect diagrams, or Fishikawa) are causal diagrams created by Kaoru Ishikawa that show the potential causes of a specific event.
Common uses of the Ishikawa diagram are product design and quality defect prevention to identify potential factors causing an overall effect. Each cause or reason for imperfection is a source of variation. Causes are usually grouped into major categories to identify and classify these sources of variation.
The defect is shown as the fish's head, facing to the right, with the causes extending to the left as fishbones; the ribs branch off the backbone for major causes, with sub-branches for root-causes, to as many levels as required.
Ishikawa diagrams were popularized in the 1960s by Kaoru Ishikawa, who pioneered quality management processes in the Kawasaki shipyards, and in the process became one of the founding fathers of modern management.
The basic concept was first used in the 1920s, and is considered one of the seven basic tools of quality control. It is known as a fishbone diagram because of its shape, similar to the side view of a fish skeleton.
- Highly visual brainstorming tool which can spark further examples of root causes
- Quickly identify if the root cause is found multiple times in the same or different causal tree
- Allows one to see all causes simultaneously
- Good visualization for presenting issues to stakeholders
- Complex defects might yield a lot of causes which might become visually cluttering
- Interrelationships between causes are not easily identifiable
Root-cause analysis is intended to reveal key relationships among various variables, and the possible causes provide additional insight into process behavior.
The causes emerge by analysis, often through brainstorming sessions, and are grouped into categories on the main branches off the fishbone. To help structure the approach, the categories are often selected from one of the common models shown below, but may emerge as something unique to the application in a specific case.
Typical categories include:
The 5 Ms (used in manufacturing)
- Manpower / mind power (physical or knowledge work, includes: kaizens, suggestions)
- Machine (equipment, technology)
- Material (includes raw material, consumables, and information)
- Method (process)
- Measurement / medium (inspection, environment)
These have been expanded by some to include an additional three, and are referred to as the 8 Ms:
- Mission / mother nature (purpose, environment)
- Management / money power (leadership)
In addition to following identified sources that can affect the desired outcome of a process or preclude opportunities:
- Mother Nature
you could take into account also:
7. Mandatory matters: such as the rules which originate from laws, standards, Body regulations or organization policies/ways of conduct
8. Matter-of-fact technology limitations: no way to reduce to zero failure risk
9. Misinterpretation of reality: science represents reality by means of models but complete knowledge of reality is not attained.
Moreover in addition to 9M model items you may consider also:
10. Mind bias: the fact that individual behaviour and choices may be driven by cultural, historical and own experience context.
The 8 Ps (used in product marketing)
This common model for identifying crucial attributes for planning in product marketing is often also used in root-cause analysis as categories for the Ishikawa diagram:
- Product (or service)
- People (personnel)
- Physical evidence (proof)
The 8 Ps are primarily used in product marketing.
The 4 or 5 Ss (used in service industries)
An alternative used for service industries, uses four categories of possible cause:
- Often an important 5th S is added - Safety
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