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The Cause & Effect (CE) diagram, also sometimes called the fishbone diagram, is a tool for discoveringall the possible causes for a particular effect. The effect being examined is normally some troublesomeaspect of product or service quality, such as 'a machined part not to specification', 'delivery times varyingtoo widely', 'excessive number of bugs in software under development', and so on, but the effect may alsorelate to internal processes such as 'high rate of team fai lures'.

The major purpose of the CE Diagram is to act as a first step in problem solving by generating acomprehensive list of possible causes. It can lead to immediate identification of major causes and point tothe potential remedial actions or, failing this, it may indicate the best potential areas for further explorationand analysis. At a minimum, preparing a CE Diagram will lead to greater understanding of the problem.

The CE Diagram was invented by Professor Kaoru Ishikawa of Tokyo University, a highly regardedJapanese expert in quality management. He first used it in 1943 to help explain to a group of engineers atKawasaki Steel Works how a complex set of factors could be related to help understand a problem. CEDiagrams have since become a standard tool of analysis in Japan and in the West in conjunction withother analytical and problem-solving tools and techniques.CE Diagrams are also often called Ishikawa Diagrams, after their inventor, or Fishbone Diagramsbecause the diagram itself can look like the skeleton of a f ish.

Use it when you start investigating a problemConstruct a CE Diagram whenever you need to investigate the causes or contributing factors for an effect(be it a quality characteristic or other outcome) which is of concern to you. This will most likely be afteryou have conducted a general investigation of problems for a particular function, product, or service, andranked them using a Pareto Chart. The effect ranked highest provides the starting point for a CEDiagram.

For example, you may just have completed an investigation of all the reasons recorded for goods beingreturned by customers and found that the highest incidence relates to incorrect goods being sent. A CEDiagram can be constructed to explore the possible causes for this.

Developing a CE Diagram in a team meeting is a very effective technique for,

y concentrating team members' attention on a specific problem

y pooling, and reflecting back, team thinking

y constructing a picture of the problem at hand without resorting to the tight discipline of a flowchart

How to draw CE diagramThis is a three step process.

Step 1Write down the effect to be investigated and draw the 'backbone' arrow to it. In the example shown belowthe effect is 'Incorrect deliveries'.

Step 2

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Identify all the broad areas of enquiry in which the causes of the effect being investigated may lie. Forincorrect deliveries the diagram may then become:

For manufacturing processes, the broad areas of enquiry which are most often used are Materials (rawmaterials), Equipment (machines and tools), Workers (methods of work), and Inspection (measuringmethod).

Step 3This step requires the greatest amount of work and imagination because it requires you (or you and yourteam) to write in all the detailed possible causes in each of the broad areas of enquiry. Each causeidentified should be fully explored for further more specific causes which, in turn, contribute to them.

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You continue this process of branching off into more and more directions until every possible cause hasbeen identified. The final result will represent a sort of a 'mind dump' of all the factors relating to the effectbeing explored and the relationships between them.

Different types of CE DiagramThere are three different types of CE Diagram. The basic type explained above is called theDispersionanalysis type. The other two are the Production process classification typeand the Causeenumeration type.

Production classification typeThis type differs from the basic type above in that each discrete stage in the production process leadingup to the effect being examined is shown along the main arrow or 'backbone' of the diagram. Possible

causes are then shown as branches off these as shown in the illustration overleaf.

This type of CE Diagram is often easier to construct and understand because those involved are alreadyfamiliar with each of the production steps identified.

Cause enumeration typeThis is not so much a different type of diagram but a different method of constructing a diagram. Insteadof building up a chart gradually (starting with the 'backbone', deciding broad areas, then adding more andmore branches), you postpone drawing the chart and simply list all the possible causes first. Then drawthe chart in order to relate the causes to each other. This method has the advantage that the list ofpossible causes will be more comprehensive because the process has a more free-form nature. Thedisadvantage is that it is more difficult to draw the diagram from this list rather than from scratch.

This method of drawing a CE Diagram can be used in conjunction with Brainstorming by using it to distilthe brainstorm output down into a logical and useable set of information.

What to do with the completed CE diagramMost of the value of CE Diagrams lies in the process used to produce them. This process leads to ideasand insights into the problem which you would not otherwise have had, and which will give you leads forfurther investigation or for experimenting with possible solutions.

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When developed by a team, the CE Diagram becomes a sort of 'shared conceptual space' in which theproblem is examined in common by all team members with the results that,

y possibilities will be uncovered which would otherwise have remained hidden

y all team members will benefit from each other's contribution and develop a commonunderstanding of the problem

Since it takes some time to get to the heart of most problems, the CE Diagram can also be used as aworking document which is changed as new data is collected and different solutions tried.

Good and bad CE diagramsA good CE diagram is one which explores all possibilities so it is likely to be large and complex-looking astwig after twig sprouts for each new related idea noted down. Be suspicious of CE Diagrams with fewfactors, or which are neat and well ordered. These may reflect a lack of knowledge of the situation, orshow that the effort to draw the diagram was not creative and exhaustive enough.