Techniques (Methods) of RCA: 5-Why's and Ishikawa Diagram

Techniques/Methods used to perform RCA:-

There are many techniques that can be used to carry out RCA but “5-WHY’s” and “Ishikawa Diagram” are the most popular ones and hence I am explaining them in detail in this blog post.

5-WHY’s:-

This technique was developed by Sakichi Toyoda, founder of Toyota Industries Co. Ltd. In this technique a series of five questions are asked in order to reach to the root cause. In some cases the questions asked could be more or less than five questions as five questions may not always be sufficient to lead to the root cause. But if the questions asked are proper and within context then in normal circumstances 5-WHY’s will lead to the root cause. In this technique the problem that has to be analyzed is written down and the question asked is generally why it happened. The answer to the problem is written down and this process is iterated until the root cause is reached.

This technique is very basic in nature and takes a fairly small amount of time and does not require any software or other materials. All you need is a paper and a pen and you can start as there is no analysis of statistics involved. However only one root cause can be found for the problem being analyzed using this technique. Also if two different people are analyzing the same problem using this technique they will point out different root causes. If however the answer to the “WHY” question being asked currently can be verified on the spot of the occurrence of the problem the issues discussed above can be avoided.

An example on how find the root causes by using 5-WHY’s:-

1    1. Why is your computer not operating?

          - Because the operating system crashed.

2    2. Why did it crash?

          -  Because it was infected by a virus.

3    3. Why was it infected by virus?

          - Because I had not installed an anti-virus software on my computer.

Ishikawa Diagram:-

Ishikawa Diagram is one of the oldest techniques used for RCA and was developed by Karou Ishikawa who used it in the 1960’s. It is also known as cause and effect analysis or fishbone diagram. The reason why it is known as fishbone diagram is because its shape resembles the bone of a fish.

 In this technique all the possible causes and their effects for the problem are listed down. An Ishikawa diagram generates and sorts hypotheses about possible causes of problems within a process by asking participants to list all of the possible causes and effects for the identified problem. The links between the events and their causes which could be actual or potential are shown by this technique in the Ishikawa diagram. Thus a very large amount of information can be represented using this technique. This information is then used to generate ideas as to why the problem (or cause) occurred and what could be the possible effects of that problem (or cause).

                       

                      Fig. A sample template showing the layout of the “fishbone diagram”.

A template should be constructed as shown in the figure. The effect (or problem) should be written in the box on the right hand side as shown in the Fig. The effect should reflect what is happening and must be defined without any ambiguity. The categories are identified and written on the top of the slanting lines that come out from the horizontal line. Many authors tend to give a specific list of categories in which the causes should fall but in my opinion the categories of causes should depend on the type of problem. Hence you can use those categories that suit your problem the best. Once the categories have been identified, the underlying causes in each category are found out and written in the form of sub branches to the categories as shown in the Fig. After this step, questions in the form of ‘why this happened’ are asked to identify why that cause took place. The answer to these questions forms the sub branches for the cause as shown in Fig. There is no restriction as to how many questions should be asked as it should be continued until almost all the aspects as to why the cause took place have been covered. Once all the causes have been discussed and dissected in detail, the root cause can be traced. The best method to do this is to establish the chain of events in such a way that the answer to the ‘why’ question traces back to the effect block.

The biggest advantage of Ishikawa diagram is that it gives all the causes that may have an effect on the system. This is useful as it can lead to the discovery of more than one root cause. It is a very useful technique for RCA when using a team to analyze the problem as it keeps everyone involved. The ideas are arranged in logical groups and one cause leads to another. Once the causes have been listed various countermeasures are applied to check whether they solve the problem. This can lead to the wastage of time, money and effort. This technique only gives what could be the root cause to a problem. In order to establish a root cause data must be collected and used to verify each cause which may be thought of as a root cause. As the diagram tends to be complex and large, if it is not drawn appropriately it may result in overlooking of important causes which must be avoided. The best part is that it is easy to carry out and to get started you don’t need any software or other tools.

Besides ‘5-WHY’s’ and ‘Ishikawa Diagram’ there are number of other methods devised over the years. All of them have their particular importance for specific fields in which they can be employed. Cause and Effect Analysis (Tree Diagram), Failure Mode and Effects Analysis, Pareto Analysis, Fault Tree Analysis, Bayesian Inference, Cause Mapping, Barrier Analysis, Change Analysis, Causal Factor Tree and Analysis, Taproot, Apollo Root Cause Analysis (ARCA), RPR Problem Diagnosis, Kepner-Tregoe Problem Solving and Decision Making, Management Oversight and Risk Tree (MORT) Analysis are the other RCA techniques that are widely used.

Next and the final post for RCA on my blog will be regarding an indepth analysis of root cause analysis.

Previous Posts on Root Cause Analysis Phases and  Root Cause Analysis Introduction