What is a Cause & Effect Diagram?

A cause & effect diagram is a simple but very effective tool that helps to identify, sort, and display potential or real causes of a specific problem or quality characteristic. It can also be used to graphically illustrate the relationship between a given outcome and all the factors that influence the outcome. Because of its function of relating causes to their effect, it is referred to as a cause-and-effect diagram. It is also called a fishbone diagram because the design of the diagram looks much like the skeleton of a fish. It is also known as Ishikawa diagram because it was invented by Dr. Kaoru Ishikawa (1915-1989), a Japanese consultant, and father of the scientific analysis of causes of problems in industrial processes. He first used this diagram in 1943 at Kawasaki Steel Works.

Why Use a Cause & Effect Diagram?

A cause & effect diagram helps to determine the causes of a problem or quality characteristic using a structured approach. It encourages group participation and utilizes team knowledge of the process. It uses an orderly, easy-to-read format to diagram cause-and-effect relationships. It increases knowledge of the process by helping everyone to learn more about the factors at work and how they relate. It indicates possible causes of variation in a process and identifies areas where data should be collected for further study.

When Use a Cause & Effect Diagram?

Use cause & effect diagram when you want:

  • To identify the possible causes or the basic reasons, for a specific effect, problem, or condition.
  • To sort out and relate some of the interactions among the factors affecting a particular process or effect.
  • To analyze existing problems so that corrective action can be taken.

Steps in Creating a Cause & Effect Diagram

Step 1: Arrange a brainstorming session with the process team. It is recommended to form a team for "brainstorming". Gathering a team of 4-7 individuals is recommended.

Step 2: Identify, clearly state and agree on the effect or the problem to be analysed. A problem can be defined as a discrepancy between existing and a desired state of affairs. A problem exists when there is a difference between what "should be" and what "is"; between the ideal and the actual situation. Identifying a very clearly defined and specific problem is the first critical step to successfully implementing any problem-solving process. A symptom differs from a problem in that the symptom is an evidence of the existence of a problem

Step 3: Place a white board or flipchart where everyone could clearly see it.

Step 4: Draw a box containing the problem or effect to be analysed, on the right side of the board with a horizontal spine.

Step 5: Add main categories of possible causes of the problem. Causes in a cause & effect diagram are frequently arranged into the following categories:

  1. The 6 Ms: Machine, Method, Materials, Measurement, Manpower and Mother Nature (Environment) (recommended for manufacturing industry).
  2. The 8 Ps: Price, Promotion, People, Processes, Place / Plant, Policies, Procedures & Product (recommended for administration and service industries).
  3. The 4 Ss: Surroundings, Suppliers, Systems, Skills (recommended for service industries).
  4. The Processes: Process 1, Process 2, Process 3 and so on.