The 5 Whys: Root Cause Analysis Made Simple

The 5 Whys is a simple way to find the root cause of a problem: state the problem, ask why it happened, then ask why again of each answer until you reach a cause you can actually change. The technique is usually credited to Sakichi Toyoda, founder of the Toyota group, and Taiichi Ohno made it a standard part of the Toyota Production System.

Five is a guide, not a rule. Some problems reach a root cause in three whys, some take six. Stop when the answer is something you can fix, and fixing it would stop the problem happening again.

Why it works

Most businesses fix symptoms. A customer complains, someone apologises and sends a credit, and the same thing happens next month. The 5 Whys takes you past the symptom to the process gap underneath. Fixing that gap stops the problem for good, rather than paying for it again and again.

Worked example

A heating firm notices that service visits often need a second trip.

• Problem: three boiler services last month needed a second visit.
• Why? The engineer did not have the right part.
• Why? The van stock did not include it.
• Why? Van stock was set two years ago and never reviewed.
• Why? Nobody owns the van stock list.

The root cause is a missing owner, not a forgetful engineer. The fix is to name an owner and review the list each quarter against parts actually used. Restocking that one part would only have fixed this month's version of the problem.

Check your logic

Read the chain backwards, joining each step with "therefore": nobody owns the list, therefore it was never reviewed, therefore the part was not stocked, therefore the engineer did not have it. If any link sounds wrong, a step is missing or the chain has gone off course.

Fill in your own 5 Whys

The worksheet keeps your analysis, the action and the owner together. Email it to yourself as a PDF to keep a record.

Common mistakes

• Stopping at a person. "Dave forgot" is never a root cause. Ask why the process allowed Dave to forget.
• Jumping to a fix. Write each answer as a fact you could check, not a solution.
• Guessing. Go and look at where the problem happened. Answers from a meeting room are often wrong.
• Following only one path. If a problem has several causes, draw a fishbone diagram first and run the 5 Whys on each main branch.
• No owner. A root cause with no named owner and date is just an interesting conversation.

When to use it

Use the 5 Whys for problems that recur and have a fairly clear chain of cause and effect. If a Pareto analysis shows one cause dominates, run the 5 Whys on that cause first.