Fishbone Diagram: A 5 Step Guide to Root Cause Analysis

Fishbone Diagram (Ishikawa Diagram)

A Fishbone Diagram, also known as an Ishikawa Diagram or a Cause-and-Effect Diagram, is a visualisation tool for categorising the potential causes of a problem (the "effect") to identify its root causes. Its structure resembles the skeleton of a fish.

It's an excellent tool for structured brainstorming in a team environment because it ensures that all potential causes across different categories are considered, preventing a focus only on the most obvious symptoms.

How to Create a Fishbone Diagram

The process involves five main steps:

1. Define the Problem (The Head)

• The problem statement, or the "effect," is written at the far right of the diagram and is enclosed in a box or the "head" of the fish.
• A long horisontal arrow (the "spine" or "backbone") is drawn pointing to the problem statement. Example Problem: "Customer churn rate increased by 25% in Q3."

2. Identify Major Cause Categories (The Main Bones)

• These are the large, general areas where the causes most likely reside. They are drawn as diagonal lines (the "main bones") branching off the central spine.
• The most common categories often depend on the industry:
• — Manufacturing (The 6 M's): Manpower (People), Machine (Equipment), Methods (Process), Materials (Input/Supplies), Measurement (Inspection/Data), and Mother Nature (Environment).
• — Service/Marketing (The 8 P's): Product, Price, Place, Promotion, People, Process, Physical Evidence, and Performance.

3. Brainstorm Possible Causes (The Smaller Bones)

• For each major category, brainstorm all possible factors that could contribute to the problem. These specific causes are written as smaller lines branching off their respective main category bones.
• This is the phase where you use techniques like the “5 Whys” on each major cause to dig deeper. Sub-causes are added as smaller lines branching off the main cause lines.

4. Analyse and Prioritise

• Once the diagram is complete, the team analyses the complexity and depth of the bones.
• Causes that appear multiple times or have many sub-branches are often the most likely root causes. Techniques like voting can be used to prioritise the top 3-5 causes.

5. Take Action

• Develop solutions and corrective actions focused specifically on the identified root causes to ensure the problem does not recur.

This structured visualisation helps teams move beyond surface-level symptoms and systematically target the fundamental issues within the system.