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What is Ishikawa diagram?

The Ishikawa diagram portrays the causes of an effect and is used in manufacturing and other services such as product development. It outlines a process and its steps, shows where quality control problems might appear, and determines which resources are needed at given times. 

Who invented it?

It was first designed by Kaoru Ishikawa in the 1960s to measure the processes of quality control. It was also first applied in the shipbuilding industry. 

Different names

The Ishikawa diagram is also popularly termed a fishbone diagram. The Ishikawa diagram is called a fishbone diagram because, you guessed it, it resembles a fish with the body showing the causes and the head the final outcome or final event. Respective of its name, the diagram (causal diagram) shows the causes of one event. 

Main purposes

The diagram’s main purpose is to let management determine which problems or causes have to be tackled in order to promote or avoid a specific event. 

Other important purposes of the diagram include using it as a methodology for developing product designs that fix practical problems. 

It’s also used in quality defect prevention to bring to light factors that cause a negative effect. 

Steps in making an Ishikawa diagram:

The Ishikawa diagram is very simple to make and you need only basic materials to get it done, materials such as a whiteboard, flip chart and marking pens. There are also a few very easy to do steps:

1. Decide on a problem or negative effect
2. Put down the problem in the center of the drawing tool, box it then draw an arrow going to it
3. Think of the main categories of causes for the problem or negative effect. If you find this too hard you can use general categories such as:
   • Methods
   • Machines (equipment)
   • People (manpower)
   • Materials
   • Measurement
   • Environment
4. Put down the causes as branches from the main arrow
5. Brainstorm possible causes and ask ‘Why does this happen?’. Each answer should be a branch from the appropriate category
6. Ask the question ‘Why does this happen?’ again. Put down sub-causes branching from the causes. Keep asking ‘Why’ to come up with deeper and deeper causes
7. When you’re all out of ideas, look to parts of the chart where ideas are weak

Tips for a great Ishikawa diagram:

There are also a few tips that you can use to make a team better design an Ishikawa diagram.

1. Use the Ishikawa diagram to help the team stay focused on the causes of the effect and not its symptoms
2. Leave plenty of space between major categories so you can add detailed causes afterward
3. Write the causes on sticky notes when brainstorming and go around the team asking each individual for one cause. Keep the rounds going until no more ideas come up
4. Motivate each individual in the team to take part in brainstorming and make their opinions heard
5. Keep repeating the question why until you get to the root problem

The Ishikawa diagram’s main value comes from the ability to dig deep and go beyond the initial incident report and better understand what in the system or process is causing the negative effect. 

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