Five Why – interrogative technique


Five Why Method

1. Author: Sakichi Toyoda (1867 –1930), Japanese inventor and industrialist, who is referred to as the “King of Japanese Inventors”.
2. History: The technique was originally developed by Sakichi Toyoda and was used within the Toyota Motor Corporation during the evolution of its manufacturing methodologies. Due to the simplicity and effectiveness five why method it becomes part of many methodologies like Kaizen and Six Sigma. In other companies, it appears in other forms. By 1917, the “Five Ws” were being taught in high-school journalism classes.

3. Essence and main goal of the method

5 Whys is an iterative interrogative technique used to explore the cause-and-effect relationships underlying a particular problem. The primary goal of the technique is to determine the root cause of a defect or problem by repeating the question “Why?” Each answer forms the basis of the next question.

4. Main functions

1. The 5 Whys is a powerful tool for engineers to help get to the true causes of problems
2. This Method is used as part of applying lean methodologies to solve problems, improve quality, and reduce costs.

5. Main rules

1. Foster an atmosphere of trust and sincerity.
2. Base our statements on facts and knowledge.
3. Try to make our answers more precise.
4. Look for the cause step by step. Do not jump to conclusions.
5. The last answer points to a process that is not working well or does not exist.

6. Procedure and Basic stages

1. Identify the problem for which root cause to be find out. Write down the problem and make sure that all people understand it.
2. Ask “Why the problem has happened?” you will get an answer.
3. Take the first answer and again ask “Why?”
4. Do such five iterations and you will get the root cause of the problem.

7. Advantage

Five Why method is an effective tool to find root cause of a problem

8. Disadvantages and Restrictions

1.Not all problems have a single root cause. However, there is tendency to isolate a single root cause, whereas each question could elicit many different root causes.
2. The outcome still depends upon the knowledge of the people involved. Thus, investigators cannot go beyond the current knowledge and find causes that they do not already know.

An Example of How to Use Five Why Method

Example from “What a Great Idea” by Chic Thompson.

1. Why has the machine stopped?
A fuse blew because of an overload
2. Why was there an overload?
There wasn’t enough lubrication for the bearings
3. Why wasn’t there enough lubrication?
The pump wasn’t pumping enough
4. Why wasn’t lubricant being pumped?
The pump shaft was vibrating as a result of abrasion
5. Why was there abrasion?
There was no filter, allowing chips of material into the pump
Installation of a filter solves the problem.


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