Root Cause Analysis: 5 Why Technique

Introduction

The 5 Why technique is originated by Sakichi Toyoda and has been applied within Toyota Motor Corporation in 1970s. It is the simplest tool used in finding the root cause of the majority of problems facing a company. It is also a great tool for auditor when assessing the root cause of analysis during auditing and processing of non-conformity. Beside that, this technique can be used during investigation of incident to find the root cause of accident.

Steps

First of all, you need to define clearly an initial cause of problems, then:

1. Ask WHY initial cause?
2. Repeat the 'WHY?' to the answer of the previous step until you feel you have reached the root cause.
3. REMEMBER! Keep asking 'WHY?' to the answer of the previous step until you feel you have reached the root cause.
• Usually the root cause will be evident before you reach the exact root cause.
• It is compulsory to keep ask 'WHY?' until 5th times continuously
• If possible, validate the apparent root cause by re-producing the cause and its effect

Example

Problem: 30% scrap rate due to faulty welding in workstation No.3

Immediate Cause: Incompetent welder

Then, start to apply 5WHY technique in order to find the root cause:

1. Why is he incompetent?
• He has not been trained adequately
2. Why has he not been trained?
• He was not included in the training plan
3. Why he was not in training plan?
•  His supervisor had not included him
4. Why the supervisor didn't include him?
• He had forgotten to evaluate the welder's competence
5. Why had he not evaluated the welder's competence?
• He had not understood this Quality Management System requirement

The conclusion is the company should provide the training to welder in terms of competency level. Beside that, the management company should provide the training to his supervisor in order him to comply with his responsibility to assure the competence of his welders.