Ishikawa diagram

Ishikawa diagram
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, cause-and-effect diagrams or Fishikawa) are diagrams that show the causes of a certain event -- created by Kaoru Ishikawa (1990). 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 these sources of variation. The categories typically include:

• People: Anyone involved with the process
• Methods: How the process is performed and the specific requirements for doing it, such as policies, procedures, rules, regulations and laws
• Machines: Any equipment, computers, tools etc. required to accomplish the job
• Materials: Raw materials, parts, pens, paper, etc. used to produce the final product
• Measurements: Data generated from the process that are used to evaluate its quality
• Environment: The conditions, such as location, time, temperature, and culture in which the process operates

Overview

Ishikawa diagram, in fishbone shape, showing factors of Equipment, Process, People, Materials, Environment and Management, all affecting the overall problem. Smaller arrows connect the sub-causes to major causes.

Ishikawa diagrams were proposed by Kaoru Ishikawa in the 1960s, who pioneered quality management processes in the Kawasaki shipyards, and in the process became one of the founding fathers of modern management.

It was first used in the 1960s, 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.

Mazda Motors famously used an Ishikawa diagram in the development of the Miata sports car, where the required result was "Jinba Ittai" or "Horse and Rider as One". The main causes included such aspects as "touch" and "braking" with the lesser causes including highly granular factors such as "50/50 weight distribution" and "able to rest elbow on top of driver's door". Every factor identified in the diagram was included in the final design.

Causes

Causes in the diagram are often categorized, such as to the 8 M's, described below. Cause-and-effect diagrams can reveal key relationships among various variables, and the possible causes provide additional insight into process behavior.

Causes can be derived from brainstorming sessions. These groups can then be labeled as categories of the fishbone. They will typically be one of the traditional categories mentioned above but may be something unique to the application in a specific case. Causes can be traced back to root causes with the 5 Whys technique.

Typical categories are:

The 8 Ms (used in manufacturing)

• Machine (technology)
• Method (process)
• Material (Includes Raw Material, Consumables and Information.)
• Man Power (physical work)/Mind Power (brain work): Kaizens, Suggestions
• Measurement (Inspection)
• Milieu/Mother Nature (Environment)
• Management/Money Power
• Maintenance

The 8 Ps (used in service industry)

• Product=Service
• Price
• Place
• Promotion/Entertainment
• People(key person)
• Process
• Physical Evidence
• Productivity & Quality

The 4 Ss (used in service industry)

• Surroundings
• Suppliers
• Systems
• Skills

Questions to ask while building a Fishbone Diagram

• People

– Was the document properly interpreted? – Was the information properly disseminated? – Did the recipient understand the information? – Was the proper training to perform the task administered to the person? – Was too much judgment required to perform the task? – Were guidelines for judgment available? – Did the environment influence the actions of the individual? – Are there distractions in the workplace? – Is fatigue a mitigating factor? – How much experience does the individual have in performing this task?

• Machines

– Was the correct tool used? – Are files saved with the correct extension to the correct location? – Is the equipment affected by the environment? – Is the equipment being properly maintained (i.e., daily/weekly/monthly preventative maintenance schedule) – Does the software or hardware need to be updated? – Does the equipment or software have the features to support our needs/usage? – Was the machine properly programmed? – Is the tooling/fixturing adequate for the job? – Does the machine have an adequate guard? – Was the equipment used within its capabilities and limitations? – Are all controls including emergency stop button clearly labeled and/or color coded or size differentiated? – Is the equipment the right application for the given job?

• Measurement

– Does the gauge have a valid calibration date? – Was the proper gauge used to measure the part, process, chemical, compound, etc.? – Was a guage capability study ever performed? - Do measurements vary significantly from operator to operator? - Do operators have a tough time using the prescribed gauge? - Is the gauge fixturing adequate? – Does the gauge have proper measurement resolution? – Did the environment influence the measurements taken?

• Material (Includes Raw Material, Consumables and Information )

– Is all needed information available and accurate? – Can information be verified or cross-checked? – Has any information changed recently / do we have a way of keeping the information up to date? – What happens if we don't have all of the information we need? – Is a Material Safety Data Sheet (MSDS) readily available? – Was the material properly tested? – Was the material substituted? – Is the supplier’s process defined and controlled? – Were quality requirements adequate for part function? – Was the material contaminated? – Was the material handled properly (stored, dispensed, used & disposed)?

• Environment

– Is the process affected by temperature changes over the course of a day? – Is the process affected by humidity, vibration, noise, lighting, etc.? – Does the process run in a controlled environment? – Are associates distracted by noise, uncomfortable temperatures, fluorescent lighting, etc.?

• Method

– Was the canister, barrel, etc. labeled properly? – Were the workers trained properly in the procedure? – Was the testing performed statistically significant? – Was data tested for true root cause? – How many “if necessary” and “approximately” phrases are found in this process? – Was this a process generated by an Integrated Product Development (IPD) Team? – Was the IPD Team properly represented? – Did the IPD Team employ Design for Environmental (DFE) principles? – Has a capability study ever been performed for this process? – Is the process under Statistical Process Control (SPC)? – Are the work instructions clearly written? – Are mistake-proofing devices/techniques employed? – Are the work instructions complete? – Is the tooling adequately designed and controlled? – Is handling/packaging adequately specified? – Was the process changed? – Was the design changed? – Was a process Failure Modes Effects Analysis (FMEA) ever performed? – Was adequate sampling done? – Are features of the process critical to safety clearly spelled out to the Operator?

Criticism of Ishikawa Diagrams

In a discussion of the nature of a cause it customary to distinguish between necessary and sufficient conditions for the occurrence of an event. A necessary condition for the occurrence of a specified event is a circumstance in whose absence the event cannot occur. A sufficient condition for the occurrence of an event is a circumstance in whose presence the event must occur. Ishikawa diagrams have been criticized for failing to make the distinction between necessary conditions and sufficient conditions. It seems that Ishikawa was not even aware of this distinction.

See also

• Seven Basic Tools of Quality

References

Further reading

• Ishikawa, Kaoru (1990); (Translator: J. H. Loftus); Introduction to Quality Control; 448 p; ISBN 4-906224-61-X OCLC 61341428
• Dale, Barrie G. et al. (2007); Managing Quality 5th ed; ISBN 978-1-4051-4279-3 OCLC 288977828

External links

• Ishikawa diagrams at ASQ
• Article from HCI Australia on Cause and Effect Diagrams
• Cause and Effects Diagrams - Pathmaker process improvement software.
• Visio Template for Cause and Effect Diagrams