Fishbone diagram

A fishbone diagram, also called an Ishikawa or cause-and-effect diagram, shows the possible causes of a problem grouped into categories. The problem is the "head" of the fish; the causes are the bones.

The usual categories (6M)

• People: skills, staffing, fatigue, supervision
• Method: procedures, instructions, maintenance plans
• Machine: equipment condition, design, wear
• Material: spares, consumables, quality
• Measurement: inspection, testing, instruments, data
• Environment: heat, dust, moisture, weather, workspace

How to build one

1. Write the problem in the head of the fish.
2. Draw the main bones, one per category.
3. Brainstorm causes under each category as a team.
4. Look for causes that appear more than once or link to each other.
5. Check the likely causes against evidence.
6. Turn confirmed causes into actions.

When to use a fishbone

Use it when the cause is unclear or several factors may be combining, for example repeat failures, quality defects and safety incidents. For a single, clear failure chain, the 5 Whys is often quicker. For serious incidents, many teams use both.

A fishbone lists possible causes. It only becomes a root cause analysis when you test those causes against facts.