The Ishikawa Diagram – A Quality Tool for Failure Analysis

Failure analysis in quality management is essential to achieve high quality – Kaoru Ishikawa already recognized this in the early 1940s. To this day, the Ishikawa diagram he developed is therefore part of the seven quality tools for failure analysis in QM. What this QM toolbox is all about and how exactly his method is to be applied, you can read in this article.

The Man with the Toolbox: Kaoru Ishikawa

Kaoru Ishikawa (1915 – 1989) was a Japanese chemist. During his professional career, he taught at the University of Tokyo, among other places, was a member of the Japanese Union of Scientists and Engineers from 1949 and worked in its research group for quality assurance. In Japan, Ishikawa is regarded as a pioneer in the field of quality: the end of World War II and the destroyed industry led to a quality offensive in the 1950s, in which Ishikawa played a major role, building on the work of William Edwards DemingJoseph M. Juran and Armand V. Feigenbaum.

He developed an employee-oriented concept for cross-divisional quality work – the concept of Company-Wide Quality Control (CWQC). This is based on the idea of Total Quality Management (TQM). A key element of the concept is therefore the quality circle, in which a group of employees works on the quality management of a company in a focused manner. Ishikawa gave this quality circle a toolbox for quality management – it still contains the Ishikawa diagram today.

Q7 – The Toolbox for Quality Management

The toolbox compiled by Kaoru Ishikawa bears the label of the “Seven Quality Tools” (Q7). Formerly intended for the quality circle, these are still of great importance today when dealing with quality problems in business processes. The tools – or rather methods – they contain are used for defect recording and failure analysis. Defect collection charts, histograms or control charts can be used to record defects, and the Pareto, flow, correlation or cause-effect diagram (also called Ishikawa diagram due to its inventor) can be used to analyze failures. The seven methods of Q7 are useful for investigating the causes of errors, thereby preventing errors in the long term, and contributing to effective problem-solving.

The Ishikawa Diagram

The Ishikawa diagram, also called cause-effect diagram or fishbone diagram due to its appearance, is a graphical representation of causes that can lead to an effect or result. The Ishikawa diagram can be used to analyze problems that occur by collecting possible causes for them and presenting them in a structured way. The goal is to identify the actual causes of a problem and to show dependencies. Complex problems can be broken down and solved in this way – which is why the Ishikawa diagram is always a welcome method in the context of a quality management system.

The Structure of the Diagram

The Ishikawa diagram is a useful tool when an identified problem can have many causes and the connections are not obvious at first glance. The problem to be analyzed is then found in the head of the fish. The different dimensions for possible causes, the eight Ms, are drawn in as fish bones:

Graphical representation of the Ishikawa diagram
  • Man:
    Persons involved and their way of communication and cooperation
  • Material:
    Resources used and their condition and storage
  • Machine:
    Work equipment such as tools or machinery and their construction, performance, and maintenance condition
  • Method:
    Process flows and organization
  • Milieu:
    External influences such as customers, laws or markets
  • Measurement:
    Calibration, key figures, and control processes
  • Money:
    Investments, liabilities, and assets
  • Management:
    Leaders, goals, decisions, strategies

The eight cause dimensions are not fixed. Dimensions can be omitted or added as needed, provided that they can have an influence on the problem to be analyzed. For the defined dimensions, possible causes are then collected and plotted in the form of small branches.

And This Is How It Works

  1. Define problem
    First, define the problem to be analyzed and enter it in your Ishikawa diagram.
  2. Collect potential causes
    Mentally play through potential causes for the problem and enter them in the branches of the appropriate categories.
  3. Check for completeness
    Check that you have considered all possible causes. Involve as many stakeholders as possible to consider different perspectives.
  4. Prioritize collected causes
    Classify the collected causes according to their strength of influence on the problem. In the following, focus on the most influential causes.
  5. Derive Measures
    Plan actions to fix the problem. Include the new measures in your action plans to solve the problem in the long term.

Learning from Mistakes with the Ishikawa Diagram

Anyone who uses a method from the Q7 toolbox and thus conducts a failure analysis in quality management ultimately demonstrates a positive approach to errors. Recognizing an error, addressing it, jointly searching for the cause, eliminating it and, above all, preventing it in the long term is laudable – but above all, it is essential for high quality. The Ishikawa diagram helps to increase the transparency of processes for the entire team and to take a deeper look at these processes. Much worse than making and analyzing a mistake is sweeping errors under the table – and leaving faulty processes as they are.

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