Ishikawa Diagrams Note

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Introduction to Ishikawa Diagrams

Also sometimes known as fishbone diagrams or herringbone diagrams

Benefits:

Shows the causes of an event

Demonstrates where quality issues might arise

Allows management to determine which issues have to be addressed in order to gain or avoid a particular event

Determine which resources are required at specific times

Drawbacks:

Not useful for complex problems

Based on opinion not evidence

Assumes problem is composed of a limited number of causes only

To successfully build a Ishikawa diagram:

Everyone must agree on what the problem is

Each line of causality must be pursued back to its root cause

Emptier branches should be grafted onto others and overcrowded ones should be split up

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Steps involved in building an Ishikawa Diagram

1. Write the problem to be solved on one side of the workspace (known as the effect), then draw the backbone of the fish

2. Decide how to categorise the causes

Manufacturing industry usually uses:

Machine

Method

Materials

Measurement

Man(People)

Medium (Environment)

Services industry usually uses the same categories but:

Remove:

Machine

Method

Replace with:

Policies (High level decisions and rules)

Procedures (Specific tasks)

3. Group potential causes into categories and sub categories

Sub categories can come from

Brainstorming, calling on prior experience of team

Data collected from check sheets or other sources

4. Quantify the relationship between the primary root causes and the effect

Regression analysis to quantify correlation

Designed experiments to quantify causation

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Example of an Ishikawa Diagram