Root-Cause Analysis Logic Tree

■ Significance & features

The logic tree is a very simple framework that is intuitive to work with even without prior knowledge, and can be practiced without worksheets or the like. For logic-tree work, an environment that lets you expand ideas without constraints—a whiteboard when in person, or a web tool like Miro when online—is better suited than PowerPoint sheets like this tool, and the author too uses these whenever possible.

However, students often cannot immediately take to workshops of the idea-expanding type, and tend to benefit from some scaffolding; also, workplace terminal environments not infrequently restrict internet use. For these reasons, we use PowerPoint sheets as a tool that can be practiced easily in any environment.

Using this tool, you can expect the following effects.

• You can derive essential solutions based on root causes, rather than ad hoc responses to the surface problem

• You can visualize the whole picture of the causes that make up a problem

• You can cultivate a perspective that seeks the essence of things and a mindset that seeks deep insight

A logic tree can be done alone, but the more a problem relates to your own work, the more strongly bias tends to apply, so—depending on the theme—it is generally more effective to do it as group work.

Note that this tool sets causes to only four levels, but once you are used to it we recommend adding up to five levels, as in Toyota’s “Five Whys.”

■ How to use

It is intended for use as teaching material in training sessions or study groups. It can be done alone, but because

• working alone, it is hard to escape bias, and

• working alone, it is hard to find a trigger to get started,

it can be said that gathering in groups of two or three members yields greater insight. It can also be done in a classroom or online format. It is better to have a facilitator, but no special skills are required.

Note that, as mentioned above, if the environment allows, it is preferable to use Miro or a whiteboard.

The concrete flow of use is as follows.

(Flow of the work)

1. First, share the purpose of the session and, if needed, do an icebreaker among participants. At this point, also share the problem to be used as the theme. Any problem may be set, but in group work use the same problem.

2. Next, explain the importance of cause analysis. Use the “Types of frameworks” explanation and the guidance materials to explain. Along with sharing what the final logic tree looks like, alert participants not to confuse it with similar concepts such as hierarchical, inclusive, or sequential relationships.

3. Have participants create a logic tree. First write the target problem at the left edge of the tree, then extend branches to the right. Trying to be exhaustive from the start tends to cause paralysis, so instruct them to first aim to dig down one branch to cause level 4, and once there, to gradually widen the branches.

   Set the time to within 10 minutes, tell them the end time in advance, and have them stop when the time limit comes.

4. Gather in groups of two or three nearby and share what the most important issue is for the theme problem. It need not be the deepest root cause. The aim is to help them notice that there is surprisingly diverse perspective even on the same problem.

5. Finally, have them share impressions of what they noticed through the work and what they would like to try going forward. The purpose is to have them put into their own words “let me try this in my own work,” motivating practice.

(Reference time allocation)

1. Introduction (5 min)

2. Explaining the logic tree and how to create it (10 min)

3. Creating the logic tree (10 min)

4. Sharing results (10 min)

5. Sharing impressions (10 min)

(Materials used)　*See the “Download” materials

• Worksheet:　Logic Tree (Why Tree) Worksheet (PowerPoint) (0.05MB)

• Guidance:　How to Create a Logic Tree (Why Tree) (pdf) (0.7MB)

■ Track record & usefulness

It has been carried out dozens of times in training on the themes of DX and problem-solving.

Below are some of the evaluations from training at a certain basic municipality (2024).

• I felt that problem-solving methods such as the logic tree are useful in taking on practical work.

• The logic tree and BPMN can be used for cause analysis and visualizing flows, so I felt it would be good to be able to use them.

• I thought I would actively use the logic tree as a way to solve problems and challenges.

■ Next steps

(Advanced training and practice)

• For cause analysis, “getting used to it” and “practice” matter above all. Because it is a general-purpose framework, we recommend applying it to various problems and building up experience.

  
  

• Other logic trees include:

  • What tree: systematically identify what to work on

  • How tree: systematically identify how to carry it out

  • KPI tree: identify the structure of what KPIs a given KPI is composed of

and others. The creation method is the same as the Why tree, so we recommend trying them in various situations.

(References and their overview)

• None in particular.

■ Glossary

• Logic tree (Why tree)

A famous method for analyzing the causes of a problem is Toyota’s “Five Whys.” In it, you repeat five times the questions “what is the cause of this event,” “what caused that cause,” and “what caused that,” thereby discovering the root cause and achieving an essential solution.

Digging into a problem’s causes can be done more systematically, and its results made easier to visualize, by using the method called the logic tree. A logic tree is a method of breaking down and identifying problems and countermeasures. As the breakdown of a single problem proceeds, it spreads out like a tree, hence the name. There are several kinds of logic tree, such as the What tree that breaks down what to do and the How tree that breaks down the means; here we use the Why tree that breaks down causes.

How far you dig into a problem’s causes greatly changes the solutions derived from it. For example, for the problem “processing paper documents is inefficient because there is so much of it,” if you stop digging at “electronic approval hasn’t taken hold,” the countermeasure might be an “electronic-approval promotion campaign.”

However, if you dig further into the cause and arrive at “services aren’t designed from the user’s perspective,” the countermeasure to take might be “reviewing the user journey from the user’s perspective.” In this way, even for the same problem, entirely different countermeasures may be taken depending on how far you dig into the cause.

This tool provides a simple worksheet for performing such cause-digging logic trees.

The logic tree is a relatively easy method for students, who are routinely asked to think logically, to accept; without any special preparation, you can start as soon as you set up a “place.” On the other hand, many students have become used to ad hoc responses and have hardly ever done cause analysis in earnest. For this reason, even a short work session can yield various insights. Moreover, the logic tree can be applied to challenges in real activities, making it highly practical.

For these reasons, the Why tree is a framework with a very high return on investment for students.