Cause and Effect Diagrams
When solving a problem as a team, there are often many views as to the problem’s root cause. The Cause and Effect diagram also known as the fish bone (structure resembles a fish skeleton) or Ishikawa diagram (named after developer, Dr. Ishikawa), is a visual depiction of cause and effect. It identifies possible causes for an effect or problem and pushes you to consider not only the most obvious possible causes but all likely. The fish bone diagram, one of seven basic tools of Quality, is mostly used in situations where little or no quantitative data is available for analysis and in brainstorming sessions to sort ideas into useful categories.
Cause and Effect Analysis
Below is the procedure to draw a Cause and Effect diagram;
1. Define problem to be solved (Effect)
- Write it at the center right of the chart or whiteboard.
- Draw a box around it and a horizontal arrow running to it
2. Identify key categories of causes of the problem e.g.;
3. Write categories of causes as branches from main arrow
4. Brainstorm all possible causes of the problem
- For each idea generated, write it as a branch from the appropriate category.
- Write causes in several places if they relate to several categories.
5. Determine Sub-causes
- For each cause write sub–causes branching off from the causes.
- Continue root cause analysis to generate deeper levels of causes.
6. When the team runs out of ideas, shift attention to places on chart with limited ideas.
How to Get the Most Out of the Cause and Effect Diagram
When completing a fishbone diagram, it is important to decide when to stop the root cause analysis by focusing the team on their “span-of-control” (areas where the team has complete control of environment) and “sphere-of-influence (areas where team is able to exert some influence but not full control). The team must operate in both these work areas to generate meaningful solutions.
Benefits of Cause and Effect Diagrams
Understanding of Root Causes
They help teams understand that there are many causes that contribute to an effect.
Illustration of Cause and Effect Relationship
Visually portray relationship of the causes to the effect and to each other.
Identification of Process Bottlenecks
They help identify areas that cause delays in the process.