Five Whys and Five Hows

Quality Glossary Definition: Five whys

The five whys and five hows techniques constitute a questioning process designed to drill down into the details of a problem or a solution and peel away the layers of symptoms. The technique was originally developed by Sakichi Toyoda who stated that "by repeating why five times, the nature of the problem as well as its solution becomes clear."

The five whys are used for drilling down into a problem and the five hows are used to develop the details of a solution to a problem. Both are designed to bring clarity and refinement to a problem statement or a potential solution and get to the root cause or root solution.

Figure 1: Five Whys Process

When to Use

While both methods are techniques to expand the horizon of a team searching for answers, there are distinct uses for five whys and five hows. However, both of these two techniques force a team to develop a better and more detailed understanding of a problem or solution and will be helpful in the root cause analysis process.

• Use the five whys technique when you want to push a team investigating a problem to delve into more details of the root causes. The five whys can be used with brainstorming or the cause-and-effect diagram.
• Use the five hows technique to develop more details of a solution to a problem under consideration. The five hows can be used with brainstorming and a solution-focused cause-and-effect diagram.

How to Use

Materials needed: Chart paper and pen/markers.

1. Draw a box at the top of a piece of flip chart paper and clearly write down the problem or solution to be explored.
2. Below the statement box draw five lines in descending order.
3. Ask "why" or "how" five times and write the answers on the lines drawn from number one to five.
4. It may take less or more than five times to reach the root cause or solution. 

Five whys technique example

Five hows technique example

Five Whys and Five Hows Resources

You can also search articles, case studies, and publications for five whys and five hows resources.

Digging For The Root Cause (Six Sigma Forum Magazine) Six Sigma training covers five popular identification tools, including the five whys technique, because some aspects of these tools are usually overlooked, such as when and where to stop and how to differentiate multiple causes through a weighing system that prevents loss of focus.

The Art of Root Cause Analysis (Quality Progress) A Master Back Belt discusses the process, the benefits, and the problems of using the five whys technique for root cause analysis.

Five Whys and a Why Not (Quality Progress) This article discusses adding a "why not?" question to the five whys line of questioning, arguing that the method will be significantly enhanced while still maintaining the simplicity of the original method.

Why Ask Why? (Quality Progress) Using the five whys technique is valuable to discovering latent causes because identifying them early can prevent other organizational issues.

Turning ‘Who’ Into ‘How’ (Quality Progress) When things go wrong, the goal should be to move away from trying to determine "who" was at fault and quickly transition into a problem-solving mindset of "how" to make things better.

Excerpted from The Public Health Quality Improvement Handbook, ASQ Quality Press.