The Cause and Effect Diagrams
This tool shows the relationship between the effect (reject) and its possible causes. It is used to logically group and identify all possible problems. It is also referred to as the “fishbone” or “Ishakawa” diagram.
To construct a cause and effect diagram:
• Use brainstorming to identify all possible causes for the effect outside experts to add to the list produced by brainstorming .
• Review the list and look for any interrelationships between the possible causes. Define three to six: major categories that can be grouped together and categorize them. Common categories sometimes referred to as the four M’s: Materials, Machines Methods and Manpower.
• Within each category, further subdivision might be required based on relationship or cause. They can ultimately be divided into groups.
•Draw the diagram, using arrows and names of each group, subgroup, and individual cause.
• Evaluate and select the most probable cause(s)，based on the problem solving group decision tools.
An example of a cause and effect diagram is given in Figure 3.6, the shipment integrity cause and effect diagram. Another chart for PCB assembly is shown in Figure 8.2. Once the most probable cause has been identified, problem solving techniques such as design of experiments (DoE) can be used to verify the problem cause and institute corrective action.