🐟 Lean Architect · Tyshchenko Lean Academy

Ishikawa Diagram

The “fishbone” — cause-and-effect analysis

“Quality control begins with education and ends with education.”
— Kaoru Ishikawa, creator of the cause-and-effect diagram
What an Ishikawa diagram is

The fishbone diagram is a tool for finding and grouping the causes of any effect. The fish head is the problem, the bones are cause categories, and the branches are the details.

WHEN TO USE IT
✓ At the start of analyzing a new problem
✓ When the causes are unknown
✓ For team brainstorming
✓ To cover every aspect of the problem
3 STEPS TO BUILD IT
1
Define the problem and its effects
State the problem → draw the fish skeleton → make sure it is a real problem, not a symptom
2
Set the main cause categories
Draw the “bones” for each category → brainstorm the detailed causes
3
Analyze the diagram
Review the diagram → mark causes with ✓ → pick the priorities for deeper study (5 Whys)
The classic 6M — cause categories
⚙️
Machines
Equipment / tools
▸ Technical condition
▸ Operating settings
▸ Part wear
▸ No maintenance plan
📦
Materials
Raw materials / inputs
▸ Raw material quality
▸ Compliance with spec
▸ Storage conditions
▸ Supplier
📋
Methods
Process / technology
▸ SOP / standard
▸ Process flow
▸ Sequence of operations
▸ Setup parameters
👷
People
Staff / operators
▸ Skills
▸ Training / SOP
▸ Engagement
▸ Work experience
📏
Measurement
Measuring / inspection
▸ Instrument calibration
▸ Measurement accuracy
▸ Inspection frequency
▸ Measuring methods
🌡️
Environment
Conditions / surroundings
▸ Temperature / humidity
▸ Lighting
▸ Noise / vibration
▸ Workplace organization
Tip: After the Ishikawa, mark with ✓ the causes worth deeper analysis. For each priority cause, run 5 Whys to find the root cause.
Ishikawa diagram — high defect rate

Problem: 7% defects in finished products. Below is a classic fishbone with the 6M categories.

7% DEFECTS in products ← PROBLEM ⚙️ MACHINES Cutting tool wear No maintenance plan 📋 METHODS No SOP Off-spec temperature 📏 MEASUREMENT Inaccurate gauges Infrequent checks 📦 MATERIALS Inconsistent quality Supplier not certified 👷 PEOPLE Low skill level No SOP training 🌡️ ENVIRONMENT Temperature swings High shop-floor humidity ✓ = priority for 5 Whys ✗ = outside our control
Analysis: After brainstorming, the team marked the priorities: No SOP (Methods) + tool wear (Machines). They ran 5 Whys on each → found the root cause → launched PDCA.
Ishikawa + 5 Whys — how they work together
🐟 Ishikawa — breadth
Covers every possible cause category. Brainstorm with the whole team. Gives you a list of candidates
❓ 5 Whys — depth
Digs into each priority branch. Finds the systemic root cause. Gives you a basis for the fix
HOW TO USE THEM TOGETHER
1
Draw the Ishikawa → collect every possible cause (brainstorm, 20–30 min)
2
Use a vote or data to mark ✓ the priorities (where the root is most likely)
3
For each ✓ cause → 5 Whys → find the root cause
4
Put in a fix that removes the root cause for good (PDCA / A3)
PROBLEM TO ANALYZE
🍱 Ready-meal defects: 6% against a 2% target
Over the past month, deviations in fat content and texture went up. The team found 12 possible causes. Your job: sort them into the 6M categories and set the priority.
CAUSES TO CLASSIFY (tap one, then pick a category):
⚙️ Worn chopper blades
📦 Fat content of raw materials
📋 No SOP for mix prep
👷 New operator with no training
📏 Thermometer not calibrated
🌡️ Shop floor at 84°F
⚙️ Mixer blade not replaced
📦 Inconsistent ingredient moisture
📋 Wrong recipe mix
👷 New QC tech not trained
📏 Scale not precise enough
🌡️ Cold room not cooling
6M CATEGORIES (tap a chip above to move it):
⚙️Machines0
📦Materials0
📋Methods0
👷People0
📏Measurement0
🌡️Environment0
5 Whys — on the priority cause
Pick the most important cause from Machines or Methods and run 5 Whys:
Why 1?
Why 2?
Why 3?
Why 4?
Why 5?
Kaoru Ishikawa — the man who taught industry to think
1
1943
The fishbone is born at Kawasaki
Kaoru Ishikawa, a professor at the University of Tokyo, drew the diagram to teach engineers to see how causes connect. The “fish” instantly made the complex easy to grasp. More than 80 years later, no one has found a simpler way.
2
1960s
JUSE — every Japanese engineer draws the “fish”
JUSE made the diagram part of its core curriculum. By the end of the 1960s it was standard across Japanese industry. Ishikawa joined Deming and Juran among the “gurus of quality.”
3
1985
6M — standard categories
The classic 6M version became standard at NASA, Boeing, and Ford. Fun fact: Ishikawa had only 4M — his followers added Measurement and Environment after noticing they were often missed.
4
Today
From paper to Miro — the principle hasn’t changed
Ishikawa died in 1989. Yet every day thousands of teams build the “fish” in Miro, Figma, or on whiteboards. Gather the team → draw → brainstorm → find the root. Nobody has come up with anything simpler.