FishboneFishbone (Ishikawa) Diagram
Ishikawa · Root Cause Analysis
What is this?
A Fishbone (Ishikawa) diagram for root cause analysis. The head is the problem — the bones are potential causes grouped by category.
What is a Fishbone (Ishikawa) Diagram?
A Fishbone diagram — also called an Ishikawa diagram or cause-and-effect diagram — is a structured brainstorming tool for root cause analysis. The "head" of the fish is the problem statement, and the "bones" are potential causes grouped into categories. The classic manufacturing categories are the 6Ms: Man, Machine, Material, Method, Measurement, and Environment (Mother Nature).
The power of the fishbone lies in its structure: by forcing the team to consider every category, it prevents tunnel vision and surfaces causes that might otherwise be overlooked. Once potential causes are mapped, teams drill deeper using the 5-Whys technique on the most likely contributors to reach the true root cause — not just the symptom.
When to use this tool
Use a fishbone diagram whenever a quality defect, downtime event, or customer complaint needs systematic investigation. It is a standard tool in 8D problem solving, A3 reports, and kaizen events. Pair it with a Value Stream Map to investigate problems discovered during current-state analysis, or use OEE data to prioritize which losses to investigate first.
Related tools
- Value Stream Map — identify systemic problems that need root cause analysis
- OEE Calculator — quantify losses to prioritize which problems to investigate
- Process Capacity Sheet — verify if a root cause fix restores expected capacity