Identifying the Root Cause Using the Tree Diagram

The tree diagram is an excellent tool to use in identifying the root cause of a nonconformance. I believe that any individual involved in the investigation of a nonconformance has his/her preferences as to which tool enables them to get the job done in an efficient and effective manner. For me, some of the benefits of the tree diagram can be summarizes as follows:
1. It clearly lays out the full range of the problem that you are investigating in a systematic, and visually expressive manner. By that I mean, you don’t have to read through multiple layers of jargon to sift out the problem. It is clearly stated in the diagram and you can clearly see how each cause is related to the problem statement simply by following the flow chart.
2. It helps to create focus around the core problem. Oftentimes, investigating teams tend to drift off the core problem they are investigating and begin to discuss other issues that are loosely connected to the problem under investigation.
3. It’s simple. The simplicity of the tree diagram begins with defining the problem statement and then connecting the dots, if you will, by asking the question “why”.
Steps to constructing the perfect tree diagram:
1. Assemble the right core team members
· The selection of team members plays a key role in the effectiveness of the group in investigating the root cause of a given nonconformance.
· You want to be sure that the members of the team are knowledgeable about the problem and can contribute to the discussions
2. Define the problem
· “A problem well stated is a problem half solved” C. Kettering. You need to ensure that the problem is clear, gets to the point of “what is wrong with what,” and is free from conclusions.
3. Construct the tree diagram
· The best tool to use is Microsoft Visio where you can click and drag the boxes onto the sheet
· With the problem statement listed in the “trunk” of the tree, you then construct the branches where you answer the question of “why”
· Remember, you are asking “why” and not “who.” One of the biggest problems that I see in my line of work training others in conducting effective root cause investigations is that they often want to answer “who” as opposed to “why”. I always stress in my trainings that it is not so much about the people, the “who” as it is about the process. If your process is ill-defined, undefined, or otherwise non-existent, it does not matter “who” is running the process. The process is broken and requires fixing.
4. Validate the diagram
· Have your diagram scrutinized by someone intimately knowledgeable about the process but was not part of the core team investigating the nonconformance.
· Ask this individual to review the diagram for completeness and accuracy. Make changes as appropriate
5. Identify the root cause
· Review the completed tree diagram and identify those issues where process improvements are required.
· The issues listed at the end of the “why” branch are often the ones that will identify the root cause of the problem. These are often process-related issues and are where you will get the “biggest bang for your buck.”