During the improve phase of a Six Sigma project, team members will use a variety of statistical and non-statistical methods and Lean tools to find underlying issues and ways to address them. In this chapter, we are going to learn more about root cause analysis and a three-step process to fix the root cause, rather than just trying to minimize the effects of the problem.
There are three basic phases to this process. They include, list the possible causes, organize them and group them into sources of causes. And then prioritize a list of causes for the next steps in our process improvement effort. Beginning with step one, let’s begin to list out the probable causes. This is often the most time-consuming step in the DMAIC improvement process. Our time could be spent conducting observations, collecting data, using techniques such as tally sheets, working with subject matter experts, and using value steam mapping to understand what’s going on in the process. What’s important is that we must have hard data in order for our quality tools be effective. Some important tools we may use include cause and effect diagrams, relational matrices, the five whys analysis, fault tree analysis, and many other tools.
Now we are going to spend some additional time on cause and effect diagrams. We categorize and group similar causes together. There are many ways we can group them. Maybe we consider where they happened in a process or the people involved. One common way of grouping causes is called the 6 Ms, which translates to man, method, machine, measurement, mother nature, and material. To explain the 6 Ms a little bit, the man category would be it was caused by people, or the persons doing the work. While the method category might indicate there’s a problem with our process. This method may also help us to reveal commonalities between the causes. After we’ve categorized the causes, we then move on to prioritizing them and identifying the vital few that we want to zero in on. A Pareto analysis can be helpful with this ranking. Perhaps after we rank the causes, we find that the people-related causes make up the largest group. We might then explore that cause in more detail by asking questions such as, are they being trained properly? Do they actually know how to properly do the task? Are they using the knowledge base properly or is it something else?