THEORY 81

ISHIKAWA’S FISHBONE MODEL

Use to analyse the cause and effect of problems.

Kaoru Ishikawa argues that it’s important to explore all of the things that could cause a quality problem before you start to think about a solution. His fishbone model, developed in 1990, is a way of analysing cause and effect and can be summarised as follows:

Ishikawa’s Fishbone Model

Source: Adapted from Ishikawa, K., Guide to Quality Control (2nd edn) (Asian Productivity Organisation, 1986).

The model is a bit like a mind map and is used to represent the problem and its causes diagrammatically. The difference with Ishikawa’s model and more conventional mind maps is that the process is linear (better for logical thinkers).

HOW TO USE IT

  • Identify and define your problem. Write it in the box at the right-hand side of the page (you can draw the box as a fish’s head if you are really keen on the symbolism). Then add the central spine of the fish.
  • Work out the major factors involved in the problem. Use brainstorming to identify as many relevant factors as you and your team can think of (see Theory 67). These factors are the ‘large bones’ running off the fish’s spine (the ones you can choke on if you’re not careful; see diagram).
  • Analyse each problem (‘big bone’) and identify as many possible causes as possible. Connect these causes to the appropriate large bone as a series of ‘medium-sized bones’ (see diagram for start of analysis of machine faults).
  • Analyse the results and investigate further. For complex causes you may have to attach ‘small bones’ to the medium-sized bones as your analysis of the problem delves deeper.
  • When complete don’t sit back and admire your artwork – do whatever it takes to test and identify which of the possible causes is actually contributing to each problem. When you know what the real problem is identify and implement a workable solution.
  • The process isn’t as complicated as it looks. Try it out on a work problem that you have already solved. I’ll bet it throws up new factors that you didn’t previously identify.

QUESTION TO ASK

  • Do I have the detailed knowledge required to identify the factors and sub-factors that might be causing the problem/s?
  • If not, who can help me?
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