Cause and effect diagrams were developed by Kaoru Ishikawa who first applied them in shipyards in Japan before and during World War II. Later, Dr W. Edwards Deming adopted this technique as part of total quality management in Japan after World War II. The cause and effect diagram or Ishikawa diagram is very helpful in the DMAIC problem solving cycle. It assists us with defining, measuring and analyzing a project or process. In this chapter, we will create a cause and effect diagram and use it to find the root cause of a problem with our process.
Creating a cause and effect diagram is a multi-step process. We begin with a clear definition of the problem or effect. Properly defining the problem is as essential as finding solutions because we must be clear about the effect or the problem that we are dealing with. The effect makes up the backbone of the fishbone diagram. Next we add various ribs to the backbone. The ribs represent the major categories of causes of the particular problem. Once we’ve added the ribs, we can label the causes. Common cause categories may include any of the six Ms, man, method, machine, measurement, Mother Nature, or material. The remaining steps are fairly straightforward. Under each of the major causes, we must consider the key factors that come into play in our process. It may be helpful to brainstorm and write down the major factors for each of these causes. Then we may need to dig deeper into the causes to ensure we have considered everything. From there, we can sit back down with our team and stakeholders in order to study and analyze this diagram very carefully.
For example, let’s consider an issue with consumer loan processing. We are experiencing delays with the processing and we would like to identify the root cause of the delays. The team has brainstormed and determined that there are four major causes, represented by the ribs in the diagram. They include loan processing staff’s inadequate skills, customers using paper applications, poor quality infrastructure when it comes to our technology and methods, and different loan amounts that may be causing inconsistencies. Once we have identified the causes, we can then begin to dig deeper to explore the key factors underneath each cause. So for example, with loan processing, we could have lack of experience, inadequate education of the team, inadequate training, and lack of motivational reward systems in play.
Next, we review the cause and effect diagram to determine the major causal factors of the problem or effect. We work together as a group to reach agreement about a clear problem statement. There may be disagreements about this which could be an indication that the problem is more complex than we originally thought. We will need to fully explore the process and possibly break it down further in order to get at the true root cause. We need to identify one priority to focus on right now. During this process, it is important to resist the temptation to start fixing things too soon. It’s important to follow the process and get down to the true issue before we start fixing anything.