What are the Five Whys? A Tool For Root Cause Analysis

Five whys (5 whys) is a problem-solving method that explores the underlying cause-and-effect of particular problems.

The primary goal is to determine the root cause of a defect or a problem by successively asking the question “Why?”. The number ‘5’ here comes from the anecdotal observation that five iterations of asking why is usually sufficient enough to reveal the root cause.

In some cases, it may take more or fewer whys, depending on the depth of the root cause.

The main benefit of the Five Whys is that it is one of the most powerful assessment methods of all non-statistical analyses. It can uncover and trace back to problems that were not very clear or obvious.

It is simple, and it works.

• Helps identify the root cause of a problem
• Understand how one process can cause a chain of problems
• Determine the relationship between different root causes
• Highly effective without complicated evaluation techniques

• For simple to moderately difficult problems
• More complex problems may require this method in combination with some others
• When problems involve human factors or interactions. So any time human error is involved in the process.

1. Begin with a specific problem. What is it that you are having an issue with? This can also help the team focus on the same problem.
2. Ask why the problem happened and write the answer down below the specific problem you listed in step one.
3. Keep asking “why” to each of the successive answers you write down until you reach the root cause of the problem.
4. Again, this may take more or less than five “why”s. Make sure your team sees eye-to-eye with each of the questions being answered as well as the final root cause.

• Distinguish causes from symptoms or causal factors
• To make sure that you are attributing the correct answer to each “why”, try working backwards. (Answer to the “Why?” + “and therefore” + the Problem Identified for that Question)
• You can break down your answers as much as you like. The more the better.
• Answers should always be based on facts and data
• Last but not least, assess the process, not the people.

The Five Whys method was originally developed by Sakichi Toyoda, the founder of Toyota Industries. This method became widely used in Toyota Motor Corporation and is still used frequently to this day. Taiichi Ohno, the architect of the Toyota Production System, describes the five whys as “the basis of Toyota’s scientific approach.”

Along with their other “go and see” philosophies, the five whys method is used along with other famous concepts such as kaizen, poka-yoke, and jidoka.

Here’s an example of how this works:

The Root Cause reveals the source of the problem. By coming up with a solution for the root cause, there is a high chance that all of the whys leading up to the final answer will naturally get resolved.

The simplest way of conducting the Five Whys test is to simply write it down on a piece of paper. However, the fishbone, or the Ishikawa diagram, can help during the initial process of identifying problems. The diagram can reveal problems that may need the five whys for a deeper look. Then, you can gather all of the root-cause-effect relationships and evaluate which of them had the greatest impact on the original problem.