The A in DMAIC is about finding the top two or three causes of the problem we are attacking. When well executed, this phase starts with team input regarding potential causes, and uses statistical methods to isolate the top 2 or 3 causes.
Explore potential causes – listen to the team
Recruiting experts who are most familiar with the product and/or process will drastically improve the team’s likelihood of a successful outcome. Team members that work with the process on a daily basis can be extremely valuable as well.
There are a number of methods for exploring potential causes, including fishbone diagrams for organizing potential variation sources and 5-Why sessions for mapping top-level symptoms to underlying root causes. Team members can collect data between team meetings and help build pareto charts and gain insight into potential causes using dot plots.
Isolate the top 2 or 3 causes
This is the most important, and often the most challenging step in a Six Sigma project. While the first half of the Analyze phase focuses on gathering team input, the second half must focus on eliminating the “trivial many” causes and identifying the “vital few.” There are a number of tools to help accomplish this task.
In manufacturing environments, we’ve found the Shainin Methods to be extremely powerful in quickly isolating the vital-few causes, without interrupting production. Techniques such as Paired Comparisons, Multi-Vari, and Components Search are among the most powerful that we have used. We highly recommend Keki Bhote’s book, World Class Quality, which details the use of these tools. Keki is a Motorola veteran who has solved some incredibly challenging problems in his time, and he is also a very motivating writer. Also, the Shainin Group is one of the best consulting teams for manuacturing problem solving anywhere. If you are a manufacturer with a sizable training budget, give them some serious consideration.
The analyze phase cannot conclude until the top causes have been confirmed. Among the most useful tools we’ve seen in this area are the Shainin Methods, hypothesis testing, regression analysis, and basic design of experiments (DOE).
Anticipating and preventing future causes with PFMEA
Effective Six Sigma teams go beyond understanding the current causes of unwanted variation, and dedicate time to anticipating and controlling other factors that could adversely affect the process in the future (this is the difference between corrective action and preventive action!). Conducting a Process Failure Modes and Effects Analysis (PFMEA) is the best method for assessing all process risks associated with one or more CTQ’s. PFMEA’s can be conducted on an entire process (which is typically the case with new product launches) or a collection of process steps that affect a CTQ of interest.