Step 2: Work Out the Major Factors Involved
After brainstorming, agree on the major categories of causes of the problem (written as branches from the main arrow). Just knowing what problem arose or may arise is not enough. You need reasons, but one reason may not be enough. The 5 Whys technique can help you to dig below the surface. These may be systems, equipment, materials, external forces, people involved with the problem, and so on.
Major categories often include 4M (Man, Machine, Method & Material) or 6M (along with 4Ms Measurement & Environment – Mother Nature).
Product marketing industries use the 8P model – Product, Price, People, Process, Place, Physical evidence, Packaging & Promotion. 4S (Surroundings, Suppliers, Systems, and Skill) used by service industries. Define possible causes categories as per the Problem and the industry dependence.