It encourages innovative thinking and still keeps the team on track in an orderly way. The 5 Whys can be applied to the brainstormed theories to get to suspected root causes. The second key strength of this tool is that its graphic representation allows very complex situations to be presented, showing clear relationships between elements. When a problem is potentially affected by complex interactions among many causes, the cause-effect diagram provides the means of documenting and organizing them all.
For the same reason, the C-E diagram has a tremendous capability of communicating to others. Construct a cause-effect diagram when you have reached the point of developing theories to guide the characterize step. The knowledge to be used to construct the cause-effect diagram comes from the people familiar with the problem and from data that has been gathered up to that point.
Some of the power in a cause-effect diagram is in its visual impact. Observing a few simple rules below will enhance that impact. Define clearly the effect or symptom for which the causes must be identified. For additional clarity, it may be advisable to spell out what is included and what is excluded.
If the effect is too general a statement, it will be interpreted quite differently by the various people involved. The contributions will then tend to be diffuse rather than focused.
They may bring in considerations that are irrelevant to the problem at hand. Place the effect or symptom at the right, enclosed in a box. Draw the central spine as a thicker line pointing to it, as in Figure Use brainstorming or a rational step-by-step approach to identify the possible causes. There are two possible approaches to obtaining contributions for the causes to be placed on the diagram: brainstorming and a rational step-by-step approach.
You, the team or its leadership will need to make a choice based on an assessment of readiness. Brainstorming would normally be indicated for a team with a few individuals who are likely to dominate the conversation in a destructive manner or for a team with a few individuals who are likely to be excessively reserved and not make contributions. Also, brainstorming may be best in dealing with highly unusual problems where there will be a premium on creativity.
If one uses brainstorming to identify possible causes, then once the brainstorming is completed, process the ideas generated into the structured order of a cause-effect diagram. This processing will take place in much the same way as described below for the step-by-step procedure, except that the primary source of ideas for inserting in the diagram will come from the list already generated in brainstorming rather than directly from the team members.
If the team members are prepared to work in that environment, a step-by-step approach will usually produce a final product in less time, and the quality of the proposed causal relationships will normally be better. In the step-by-step procedure, begin by identifying the major causes or classes of causes that will be placed in the boxes at the ends of the main spines coming off the central spine of the diagram.
It may helpful to start with some simple mnemonic lists of possible major areas as a reminder of the many possible sources of causative factors.
These are just helpful places to start. Start with one of these sets of categories and, after a while, rearrange the results into another set of major areas that fit its particular problem more appropriately. After identifying the major causes, select one of them and work on it systematically, identifying as many causes of the major cause as possible. Continue to move systematically down the causal chain within each major or secondary cause until that one is exhausted before moving on to the next one.
Ideas may surface that should apply to an area already completed. Be sure to backtrack and add the new idea. Each of the major causes not less than two and normally not more than six should be worded in a box and connected with the central spine by a line at an angle of about 70 degrees. Here, as well as in subsequent steps, it has proved useful to use adhesive notes to post the individual main and subsidiary causes about the main spine.
Since these notes can be easily attached and moved, it will make the process more flexible and the result easier for the participants to visualize. Figure 36 generalizes the diagram to this point. Add causes for each main area. Each factor that is a cause of a main area is placed at the end of a line that is drawn so that it connects with the appropriate main area line and is parallel with the central spine.
Figure 37 shows how to display a number of possible causes of problems arising from an engine, which is a main area for some larger symptom that is being explained. C-E diagrams are generally easier to read and appear more visually pleasing if the text is placed at the end of the line as in Figure Other users have placed the text on the line like Figure Text on the line tends to be harder to use and read, especially as more levels of subsidiary causes are added.
Add subsidiary causes for each cause already entered. Each of these causes is placed at the end of a line which is drawn 1 to connect with the line associated with the factor that it causes and 2 parallel with either the main area line or the central spine. Figure 39 is an amplification of the portion of a C-E diagram introduced in Step 5. Note how the governor and throttle have been added as possible causes of the wrong speed of the engine. Throttle malfunction may result from either of two causes: Faulty calibration or defective linkage.
Keeping the lines parallel makes reading easier and the visual effect more pleasing. Clearly, when one is actually working on a C-E diagram in a team meeting, one cannot always keep the lines neat and tidy. In the final documentation, however, it is found that using parallel lines makes for a more satisfactory diagram. A diagram composed of lines with random orientation like the following example is harder to read and looks less professional.
Continue adding possible causes to the diagram until each branch reaches a root cause. As the C-E diagram is constructed, team members tend to move back along a chain of events that is sometimes called the causal chain. Teams move from the ultimate effect they are trying to explain, to major areas of causation, to causes within each of those areas, to subsidiary causes of each of those, and so forth. When do they stop? Teams should stop only when the last cause out at the end of each causal chain is a potential root cause.
A root cause has three characteristics that will help explain when to stop. First, it causes the event the team had sought after—either directly or through a sequence of intermediate causes and effects.
Second, it is directly controllable. That is, in principle, team members could intervene to change that cause. In the engine example, we have been using in this section, speed cannot be controlled directly. Control of speed is dependent on proper functioning of the throttle and governor, but proper control with the throttle is dependent on correct calibration and proper functioning of the linkage.
The calibration and the linkage can be controlled. They are root causes. Third, and finally, as the result of the other two characteristics, if the theory embodied in a particular entry on the diagram is proved to be true, then the elimination of that potential root cause will result in the elimination or reduction of the problem effect that we were trying to explain.
It is only by identifying the main causes that you can permanently remove the problem, or reduce the delay. A cause and effect diagram is a tool that helps you do this. The tool can help you identify major causes and indicate the most fruitful areas for further investigation. It will help you understand the problem more clearly. By going through the process of building the diagram with colleagues, everybody gains insights into the problem, alongside possible solutions.
The people involved benefit from shared contributions, leading to a common understanding of the problem. The cause and effect diagram is sometimes called a fishbone diagram because the diagram looks like the skeleton of a fish or an Ishikawa diagram after its inventor, Professor Kaoru Ishikawa of Tokyo University.
The tool quickly helps you to fully understand an issue and to identify all the possible causes — not just the obvious. If you know the cause of the delay, you are then better placed to implement the solution. Firstly, identify the problem. Write it in a box and draw an arrow pointing towards it. Think about the exact problem in detail. Where appropriate, identify who is involved, what the problem is, and when and where it occurs.
Identify the major factors and draw four or more branches off the large arrow to represent main categories of potential causes. Categories could include: equipment, environment, procedures, and people. An alternative way of creating the branches of a cause and effect diagram is to carry out the Affinity Diagram technique and use the group headings produced there.
Background The cause and effect diagram was adopted by Dr W Edwards Deming as a helpful tool for improving quality. He has also helped develop statistical tools used for the census, and has taught methods of quality management to the military.
Both Ishikawa and Deming use this diagram as one the first tools in the quality management process. The cause and effect diagram is one of many root cause analysis tools.
So, the more elaborate the diagram, the better the chance of rooting out the problem in the process. The "causes" of variation in this characteristic are categorized into six main factors: measurement, people, environment, machines, methods and materials.
For example, a detailed cause under the "Machines" main is a dead battery. The six main factors in the diagram are often used for cause and effect diagrams. However, you may pick any factors you want to be the main factors. The steps in constructing a cause and effect diagram are given below. The most difficult thing to do with a cause and effect diagram is to analyze it after it is completed. How can you determine what the true cause is? Our next blog will examine this.
I love the use of fishbones coupled with the use of the 5 why. When cross functional teams collaberate moutains can be moved with less disfunction and effort. This is an excellent tool. Buy Now. Try Free. Click here to see what our customers say about SPC for Excel!
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