The eight disciplines of problem solving (8D) is a methodology designed to find the root cause of a problem, devise a short-term fix, and implement a long-term solution to prevent recurring problems. Five Whys is an interrogative technique used to explore the cause-and-effect relationships underlying a particular problem. The primary goal is to determine the root cause of a defect or problem by repeating the question "Why?"
Design of experiments (DOE) is an approach to engineering problem solving that applies principles and techniques at the data collection stage so as to ensure the generation of valid, defensible, and supportable engineering conclusions. DOE determines the relationship between factors affecting a process and the output of that process. It is used to find cause-and-effect relationships.
Red X problem solving strategies emphasize that most issues can be corrected by finding the root cause and controlling it. These philosophies serve as a technical problem-solving tool to understand vehicle performance issues.
Six Sigma is a disciplined, data-driven methodology for eliminating defects (driving toward six standard deviations between the mean and the nearest specification limit) in any process—from manufacturing to transactional and from product to service.