Fishbone Diagram (or Ishikawa Map)

Kaoru Ishikawa

Related Articles Root Cause Analysis Pareto's Law

The Fishbone diagram is one of the many management tools created by Dr. Kaoru Ishikawa. Ishikawa-san was thirty years old when the "little boy" and "fat man" bombs dropped on two of Japan's cities. Working in the Kawasaki shipyards, Dr Ishikawa was also witness to Japan's long road towards recovery and rebuilding which required a lot of hard work coupled with innovation and creativity.

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This was when Japan turned to advanced countries such as the United States for ideas and techniques for application in their own context. Quickly discarding their pre-war biases and prejudices, Japanese businesses embraced all management concepts developed by the Americans - for there was just no other way to lower their costs and boost their efficiency.

From an importer of knowledge and ideas, Japan became an exporter of the same when Dr. Kaoru Ishikawa's inventions and contributions in the management field began to be adopted by management and businesses throughout the world.

Cause - Effect Diagram

Simply adopting and blindly implementing American management concepts were not enough. They had to be suitably molded and seamlessly blended with the traditional Sogo shosha and Keiretsu business styles, one of whose unique features is collaborative effort expended through small groups of people. This exercise took a lot of churn and simmer. Out of this process have emerged several of the groundbreaking ideas and concepts of Japanese management; and they have taken up a special place in the world of management science today. One such tool in the realm of root cause analysis is Dr. Ishikawa's Fishbone diagram, also known as the Cause and Effect Diagram (Diagrama de Causa y Efecto ) , as well as the eponymous Ishikawa Diagram (Diagrama de Ishikawa).

As with any brilliant idea, the basic foundation of the Fishbone is extremely simple and practical. Used and understood even by non-specialists, the Cause and Effect diagram is used as a team brainstorming tool to provoke, tease and evoke more and more ideas and issues (causes) to be captured that can go into any particular conclusion (effect) being reached. When finished, after a few iterations of analyses, the diagram identifies and explains in a graphical format all the possible causes of a particular effect. All the possible causes are depicted at various levels of detail in connected branches. The level of detail increases as the branch goes outward, which means that an outer branch is a cause of the inner branch that it is attached to. This means that the outermost branches indicate the root causes of the problem.

Creating Fishbone Diagrams

While drawing the chart, care is taken to have the inner branches meet a horizontal straight line, called the "spine" of the chart. The statement of the problem - or the effect - is to the right of the spine inside a box, which makes it look like the head of a fish. When finished, the entire map resembles a fishbone.

The mandate for the collaborating team, when they sit down across the table to draw the Ishikawa diagram, is to focus on why the problem occurs. There is no effort to look at the history or symptoms of the problem, or anything else that might digress from the intent of the session. When the team comprises members from different departments or functions, each of them provides their own specialist view about why the problem (the "fish-head") occurs. It might be discovered through this brainstorming session that there are causes common across two or more departments or functions.  Perhaps that some causes permeate the entire organization. Thus, in one single snapshot, the top management gets to see exactly why the problem is likely to  be occurring.

Example Fishbone (click to enlarge) 

Usually, this is how a typical Ishikawa Diagram drawing-and-analyses scene pans out:

• First, a large writing area is put up in the center where everybody can see it. This writing area could be a flipchart or a whiteboard.
  
• The problem that needs to be addressed is defined. All team members have to be very clear about what exactly the problem is. The problem statement is described clearly and succinctly in the fish head portion.
  
• To set the ball rolling and to ensure logical control over the brainstorming process, the following fundamental blocks are listed to begin with: manpower, machines, methods, materials and environment - in case of a problem related to manufacturing; and equipment, policies, procedures and people - in case the problem facing the team relates to administration and service. Of course, when listing them, it should be clarified that these blocks are suggestive and not exhaustive. These blocks along with any other identified are major branches connecting to the spine.
  
• Each member of the team then gets a chance to come up with what they think is the cause of the problem. Per turn, only one cause may be contributed by every member, else they simply "pass" if they can't think of any cause in any particular round.
  
• Each cause thus identified is then "hung" on the branch of the category that it belongs to. For example, if "Moisture Content" is a major cause, then "Dryer's RPM" is a cause that is hung on to moisture content.
  
• In case the cause happens to be the cause of another cause which is already present, then it must be hung on the branch of the latter. For instance, "Materials" is a major branch that goes to the spine of the problem of "Recurrent pipe leakage". "Defective measurement tools" is a branch that connects to materials. "Lack of suppliers" or "Substandard supply of tools" is a cause that hangs on to defective measurement tools.
  
  It is also possible that one cause may be placed on several branches.
  
• The brainstorming session ends when a time comes where everybody passes.

Root Cause Analysis

The resulting Ishikawa Diagram is then analyzed by the senior management to draw up a plan of action to root out the causal factors, so that the root causes can solved.  This is frequently done, by taking the enumerated causes, and measuring their occurrence in various processes.  After recording these data for a specific period, the results are examined in a Pareto Chart, wherein the 80/20 rule makes it apparent where to invest the appropriate organizational effort to reduce the unwanted effects so analyzed in this process (or perhaps to increase intended postiive effects).

As can be seen above, the Cause and Effect exercise may be seen as the first step toward any quality management effort. Problem-solving techniques continue where this exercise leaves off.

An innovation on the Ishikawa fishbone is the "lateral tree", which is supposed to have an edge over the former when it comes to handling more complicated scenarios involving causal branches of several depths. The latter strives to vertically align all items on the same causal level, thus providing more perspective to analysts.

The fishbone diagram and collaborative, team-approach were integral components of Dr. Ishikawa's "Company-Wide Quality Control" (CWQC) quality strategy. His Quality Circles (QC) became popular worldwide for the fresh breath that they provided previously stale problem-solving mechanisms. In recognition of his life-long efforts of making "quality" a household word, the American Society for Quality (ASQ) instituted the Ishikawa medal in 1993, an annual award that recognizes leadership in the human side of quality.

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