What is a Fishbone Diagram, how is it used?

A Fishbone Diagram (also called Ishikawa Diagram or Cause-and-Effect Diagram) is a visual tool used to systematically identify and organize all possible causes of a specific problem or effect. It was developed by Dr. Kaoru Ishikawa in the 1960s.

The diagram looks like a fish skeleton:

• The “head” of the fish is the problem/effect you want to solve.
• The “bones” branching off the spine are the major categories of causes.
• Smaller bones branching off are the specific causes within each category.

Why use it?

• Forces teams to think through all possible causes (not just the obvious ones)
• Prevents jumping to conclusions
• Encourages cross-functional collaboration
• Very useful in root cause analysis (RCA), quality improvement, Six Sigma, Lean, etc.

How to Create and Use a Fishbone Diagram (Step-by-Step)

1. Define the problem clearly
   Write it in a box on the right (the “head”). Be specific.
   Example: “Customer complaints about late deliveries increased by 40% in Q3”
2. Draw the main spine
   A horizontal arrow pointing to the problem.
3. Identify major cause categories (the big bones)
   Common categories (the 6 Ms for manufacturing, or adapt to your industry):
   • Man (People)
   • Method (Processes)
   • Machine (Equipment/Technology)
   • Material
   • Measurement
   • Mother Nature (Environment)

   For service/industry, people often use:

   • People, Policies, Procedures, Plant/Technology, etc.
4. Brainstorm all possible causes
   Ask “Why does this happen?” repeatedly (5 Whys technique helps).
   Write each cause as a branch off the relevant category.
5. Go deeper
   For each cause, ask “Why?” again and add sub-causes (smaller bones).
6. Analyze and prioritize
   Circle the most likely root causes (use voting, data, Pareto, etc.).
7. Develop action plan
   Address the confirmed root causes.

Practical Case Study: Restaurant Getting Complaints About Cold Food

Problem (Head of the fish):
“Customers frequently complain that food arrives cold” (complaints rose from 3 to 18 per week)

Fishbone Diagram Categories Used:
We used 6 categories suitable for a restaurant:

1. People (Staff)
   • Servers forget to check food temperature before leaving kitchen
   • New staff not trained on urgency
   • Kitchen and serving staff not communicating
   • Too few servers during peak hours → delay
2. Processes (Methods)
   • No standard procedure for checking food temperature
   • Food waits too long on the pass before being served
   • Tickets not prioritized correctly during rush
   • No “food ready” notification system between kitchen and floor
3. Equipment (Machines)
   • Heat lamps broken or insufficient
   • Plates not pre-heated
   • Delivery trays too small → food stacked and cools faster
   • Old warming drawers not maintaining temperature
4. Materials
   • Some dishes (e.g., pasta) cool faster than others
   • Large portion sizes take longer to eat → perceived as cold
5. Environment (Mother Nature/Place)
   • Dining room AC set too low near some tables
   • Long walking distance from kitchen to farthest tables
   • Draft from entrance door
6. Measurement (or Management)
   • No tracking of time from “food ready” to “delivered to table”
   • No temperature checks logged
   • No customer feedback analyzed by dish/table location

Root Causes Identified After Investigation (circled on the diagram):

• Heat lamps were broken for 3 weeks (maintenance backlog)
• No policy to pre-heat plates
• Average time from kitchen to table was 4.5 minutes during peak (target should be <2 min)
• Servers overloaded: 1 server handling 9 tables instead of max 6

Actions Taken:

1. Repaired/replaced heat lamps same week
2. Implemented plate pre-heating in salamander broiler
3. Added a runner position during peak hours
4. Created a simple checklist: food temperature >60°C before leaving pass
5. Installed digital ticket system with timers

Result:
Cold food complaints dropped from 18 to 2 per week within one month.