Fishbone diagram

The fishbone diagram is also referred to as the cause and effect diagram, or Ishikawa diagram. It is considered one of the seven keys tools of quality management. Although the tool was first proposed and used by Karu Ishikawa, it is fondly referred to as the fishbone diagram due to it’s unusual shape.

fishbone diagram

Fishbone Diagram

Uses of the Fishbone diagram

The fishbone diagram is often used to identify potential root causes to problems, or process performance characteristic. In these situations, the head of diagram [or the head of fish] identifies the problem [or effect] and the prongs of the diagram [or bones] identify the potential causes [or cause] that can influence the effect.

 

There are several methods in which the potential causes of the fishbone diagram can be identified

The 6M method

The 6 M method uses a list of six generic titles that start with the letter M.

i.e.

M-Measurement

M-Method

M-Man

M-Machine

M-Materials

and M-Mother nature [i.e. environment]

Each category name represents the title of the prongs on the fishbone diagram. Once the headings are in place the improvement team can brain storm potential reasons for each of the categories.

Cause and effect method

Another method to create the categories of the fishbone diagram is to use the output of a cause and effect matrix. In this case, each of the process steps forms the heading name of the fishbone diagram and the improvement team brainstorm potential root causes for each process step from the cause and effect matrix.

cause and effect diagram

Affinity diagram method

The third method is to use an affinity diagram to create a list of potential causes. This can be done during brainstorming or kaizen. Sticky notes can be used for members of the improvement team to identify and write out possible causes for the problem or process performance. These ideas are then grouped under a general heading. The headings are used as the to populate the bones of the fishbone.

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