Fishbone Diagram

What is Fishbone Diagram?

The Fishbone Diagram — also called an Ishikawa or Cause-and-Effect Diagram — is a visual tool for mapping all potential causes of a problem across structured categories. It looks like a fish skeleton: the "head" is the problem, and the "bones" are cause categories. The classic 6M categories are People (Man), Process (Method), Equipment (Machine), Materials, Measurement, and Environment (Mother Nature). Teams use it to move beyond obvious causes and uncover systemic issues.

When to Use It

• •In Step 2 (Analyze) as the primary root cause analysis tool
• •When a problem has multiple potential causes across different areas
• •When the team needs to see the full picture before drilling into specifics
• •Before running a 5-Why analysis — the fishbone identifies which causes to investigate further

How to Use It: Step by Step

1. 1

   Draw the skeleton

   Write the problem statement at the head (right side). Draw a horizontal line (the spine). Add diagonal lines for each cause category (the bones).

2. 2

   Brainstorm causes silently

   Give each team member sticky notes. Ask them to write one potential cause per note, placing it on the appropriate category bone. Allow 10-15 minutes of silent brainstorming.

3. 3

   Cluster and discuss

   Read all notes aloud. Group related causes. Discuss each cluster — are these symptoms or root causes? Add sub-bones for deeper causes.

4. 4

   Vote on top root causes

   Use dot voting (each person gets 3-5 dots) to identify the causes the team believes are most significant. The top 2-3 become candidates for 5-Why analysis.

Pro Tips

• ✓Use the 6M categories as starting points, but rename them to fit your context (e.g., "Technology" instead of "Machine" for office environments)
• ✓Silent brainstorming first prevents groupthink and gives quieter team members equal voice
• ✓A fishbone with 30+ causes is normal — it means the team is thorough, not that the problem is unsolvable
• ✓Photograph the completed fishbone and share it — it becomes a reference for the rest of the project

Facilitation Guide

Run a 90-minute root cause workshop. Begin by reviewing the problem statement from Step 1 (5 min). Draw the fishbone skeleton on a whiteboard and have each person write causes on sticky notes in silence (15 min). Place and cluster notes on the fishbone, discussing as a group (25 min). Vote on the top 3 root causes using dot voting (10 min). Run 5-Why drills on the top 3 causes (25 min). Summarize findings and validate with available data (10 min).

Other Tools in Step 2