The ‘Fish-bone’ Root cause analysis process
Dr. Kaoru Ishikawa developed the “Fish-bone Diagram” at the University of Tokyo in 1943. Hence the Fish-bone Diagram is frequently referred to as an “Ishikawa Diagram”. Another name for this diagram is the “Cause & Effect” or CE diagram.
How does a fish-bone diagram work?
A cause and effect diagram, often called a “fish-bone” diagram, can help in brainstorming to identify possible causes of a problem and in sorting ideas into useful categories. A fish-bone diagram is a visual way to look at cause and effect. … The problem or effect is displayed at the head or mouth of the fish.
Why is a fish-bone diagram useful?
The fish-bone diagram easily illustrates the many possible reason for a process failure in a single diagram. When used as a team approach to problem solving, this simple process uncovers many less obvious potential impacts.
This tool is most effective when used in a team or group setting.
Used as a Facilitated brainstorming session, a fish-bone diagram is a great way to boost and structure the process of understanding the reasons for a certain result, because it captures all the potential and actual failure causes.
To create a Fish-bone Diagram, you can use any of a variety of materials. In a group setting you can use a white board or a flip chart to get started. You may also want to use “Post-It” notes to list possible causes and enable the team to re-arrange or re-prioritise the notes as the diagram develops. There are also several software packages that can be useful in creating a Fish-bone Diagram.
Write the problem to be solved (the EFFECT) as descriptively as possible on one side of the Paper, then draw the “backbone of the fish”, as shown below.
The example often chosen to illustrate the process is basketball “Missed Free Throws”
The next step is to decide how to categorise the causes. There are two basic methods:
- by function, or
- by process sequence.
The most frequent approach is to categorise by function.
In manufacturing settings, the categories are:
In service settings, Machine and Method are frequently replaced by Policies (high level decision rules), and Procedures (specific tasks).
In this case, we will use the manufacturing functions as a starting point, less Measurement because there was no variability experienced from measurements (it’s easy to see if the ball goes through the hoop).
Just using the categories will not give enough detail to identify specific root causes. Normally there are lots of contributors to any single problem, so an effective Fish-bone Diagram will have the potential causes listed in categories and sub-categories.
It is easy enough to get to the detail of the sub-categories by either Brainstorming with the group/team members or by using individuals with prior experiences.
See one of the strands and subcategories in the fish-bone diagram below:
Indented Hierarchy Fish-bone
An alternate format for a Cause and Effect diagram is the “indented hierarchy fish-bone”. This format may be easier to use as it can be easily executed in a word processing or spreadsheet program. Following is an example of our Free-Throw Root Cause Analysis using the indented hierarchy method:
Effect – The problem – The Made vs Missed Free Throws in basketball
Method – Shooting Mechanics
Material – Ball
Size of Ball
People – Shooter (Closely related to method in this example)
Consistency (Muscle Memory)
Adjustment to Other Variables
Environment – Weather
Wind Gusts / Sun / Rain
Outside vs. Inside
Machine – Hoop and Backboard
“Play” – Rigidity
The important part is the So What’s – what do you need to put in place to eliminate or reduce the risk of each elements impact on the problem – what action should you take
It doesn’t matter if you use a graphical representation or build an indented hierarchy Fish-bone, this process improvement tool will greatly help understanding of the significant factors involved in a process.
Creating this diagram with a cross functional team will build not only trust between departments but will cultivate newfound knowledge and understanding for the key influencers in the process. When using the Fish-bone as a discussion topic during a meeting, the participants can be focused more explicitly on process improvement and defect reduction.
Remember there is always…