Fishbone / Ishikawa Diagram
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Overview

Track the reasons behind challenges and problems in any domain using this hierarchy based tool — bonus, it looks like a fish, what’s not to like? 

The Fishbone or Ishikawa Diagram is a visual tool to identify cause and effect relationships as part of a root cause analysis and improvement process. 

HOW IT'S USED.

Considered one of 'seven core quality tools', the diagram is generally used as a collaborative brainstorm process to generate potential causes from key categories and break down immediately obvious causes within those categories into sub causes. 

Thus it explores causal effects via breadth, through considering a range of categories, and depth, by digging beyond the cause into sub causes. 

POSSIBLE CATEGORIES.

The categories might vary, depending on your needs you might consider:

  • 5M/1E for manufacturing, based on the original use of the diagram, incorporating machine, methods, measurements, material, people (originally ‘manpower’), and environment.
  • 8Ps for marketing, expanded from the 4Ps of marketing, to incorporate product, price, promotion, place, people, process, packaging, and physical evidence. 
  • 5Ss for service industry, incorporating supplier, surroundings, systems, scope of skills and standard documentation. 
  • 6Ps for work improvements, incorporating policy, process, people, plant, program and product. 

IN YOUR LATTICEWORK.

The Fishbone Diagram makes the 5 Why approach for root cause analysis seem more lightweight, given the latter tends to focus in a single area — however, consider combining the two approaches for best effect. There are a number of models that might inspire the categories you use, such as the 4Ps of Marketing. And you might want to use this approach to avoid challenges involved in navigating Correlation vs Causation.

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Actionable takeaways
  • Identify the problem, or effect. 

Define the problem or end effect that is being investigated and write this in the ‘head’ of the Fishbone Diagram. This anchors the rest of the conversation. 

  • Identify relevant and useful categories. 

Use the list in the overview as a starting point but change as required. There are no set rules, they simply serve as a checklist to ensure that you are considering a range of areas. Capture these categories as branches, or main bones from the fish spine.

  • Brainstorm high level causes. 

Ask ‘why does this happen?’ to generate a list of causes in each category, captured along the bones. 

  • Brainstorm sub causes. 

Now turn your attention to the causes and again ask ‘why does this happen?’ to dig deeper and identify sub causes, captured on ‘bones’ that branch of the main one. 

  • Analyse results and consider next steps. 

After completed, the diagram can be analysed to identify high impact areas and potential improvement strategies.

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In Practice

Internal damages at IKEA.

This paper from Ikea in Portugal describes a process improvement process to address the level of internal damages in Ikea stores. The diagram below was part of a broader analysis process.

Limitations

The main issues with the diagram are the differentiation between causes and sub causes. For example, some causes might be complex, with many elements below them, becoming impractical to capture in the diagram. By breaking it up into separate categories, the diagram also does not lend itself to a more connected view of challenges. 

Finally, there is no clear prioritisation within the diagram — all causes seem equal, when in reality a sub cause, which is visually small, might be the key issue. Other causes and sub causes therefore might become a distraction.

Build your latticework
This model will help you to:

The fishbone or Ishikawa diagram, also known as the cause-and-effect diagram, is a core tool within quality management and is commonly used for improvements in products, manufacturing and other fields. 

Use the following examples of connected and complementary models to weave the fishbone diagram into your broader latticework of mental models. Alternatively, discover your own connections by exploring the category list above. 

Connected models: 

  • 5 Whys: in digging to root cause, use this as part of the fishbone process. 
  • Second order thinking: to go beyond the initial cause to sub causes. 
  • 4Ps of marketing: as possible categories. 

Complementary models: 

  • Risk matrix: to consider potential issues with consequences versus likelihood. 
  • Chain reaction/ domino effect: to consider the flow on effects of potential issues. 
  • First principle thinking: to identify and go below assumptions. 
  • Occam’s razor: to cut to the core of the issue. 
  • Divide and conquer: separating out and addressing potential causes.
Origins & Resources

The Fishbone Diagram was created by quality management pioneer Professor Kaoru Ishikawa in 1968. Ishikawa, an engineer, was a leader of quality management at Kawasaki at the time. In his 1986 book, Guide to Quality Control, Ishikawa argued that there were six other key quality tools in addition to what he called the ‘cause-and-effect diagram’, which were: control chart, histogram, flow chart, run chart, scatter diagram and Pareto chart. 

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