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The Cause and Effect Diagram
What is a cause and effect diagram? You will likely see a Cause and Effect diagram as part of quality or problem solving within your project. It breaks down the causes of a problem or problem statement which has been identified, and it breaks it down into certain branches. It’s a method of brainstorming and we usually have our problem statement at the end and the problem areas off the spine.
Because of this, it looks like a fish or a fish bone, which is why it’s also known as a fishbone diagram. All of these branches are used to break our problem down to help identify the main cause, or the “root cause” of a problem.
It’s also called an Ishikawa diagram after Kaoru Ishikawa from the University of Tokyo who invented this idea.
Let’s look at a quick example. The problem or the “problem statement” is placed at the head of the fish, and the reasons are brainstormed in the categories that you might choose. Some popular categories that you will find are People, Information, Processing, System or “PIPS” as it’s known. This is pretty well known in Lean or the Toyota production system.
You might also see in manufacturing other categories: Man, Method, Machine and Material.
Ultimately, you can put anything you like here, but this just gives us a framework to view the problem through. We can ask, “What information are people not getting?” or do we have the right people on board here? or “Is the process not up to scratch?” Do we need to change the process to fix this particular problem, or is the system hindering us. Do we have the wrong system, is there a bug in the system, is the system not quite up to scratch, is it not performing as we expected?
All of those things might contribute to the problem, and that’s just the lens that we view our problems through to help us find the real cause or the root cause of a problem.
That is a cause and effect diagram.
– David McLachlan