Thursday, September 20, 2012

Fish Bone Alone Doesn't Deliver Root Causes

Chances are, fish bone or Ishikawa diagrams alone will not get you to the root causes. I refer to the fish bone as basic root cause tool. They serve a purpose and they do enable root cause investigations but they do not necessarily have the power to be a stand alone tool.
Let's talk about why and then what they are very good for.
The reason they are not able to give you all the root causes comes from the way they are used. In general they produce a categorized list physical causes and human causes but they do not identify  causal chains or underlying systemic or latent causes. Many times they only feature the symptoms of these latent causes as the bones of the fish. If you choose to only use the fish bone you have the potential to miss many issues and the connections that tie them together. I have reviewed many of these diagrams where the real root causes were just under the surface of the list but never brought to light during the investigation.
The real focus for me is the return on investment and if my root cause program is driven by only fish bone than I am implementing more solutions trying to address all of the identified bones of the fish at additional cost and I am more than likely suffering reoccurring failures driving lost production and additional analysis cost.
So what do I use the fish bone for? Personally I like to use it in three ways first as a lead in to the FMEA when working with a group that may have not used that tool before. I would take the bones of the fish and transition them over to a spread sheet or FMEA tool. This can help me get folks engaged and help to began the population of the next tool.
The second way that I use the fish bone is to is as a brain storming tool where we can identify many things that could have caused the failure and then I assign the individual bones to groups and they go out and look for data to confirm or deny the existence of that cause. Then when the team gets back together to apply the next tool and pursue root causes and solutions we have data to keep the process moving.
The third reason that I use the tool is as a facilitation exercise for when I have a quite or boisterous root cause team or team members. In this situation we use stick notes and we all write and stick causes to the diagram. This give the less expressive folks and alternative in writing instead of speaking and it allows the expressive folks to see the sticky note and know they were heard. This can get a group to develop many more possible causes and then they can verify, investigate and eliminate with data producing a better lead in to the next more thorough tool in your root cause process.
So to wrap it up fish bone analysis is a tool that has its place in the root cause process but if you want the lowest total cost of solution you will need to couple it with other tools from your root cause tool box. To read more on root cause check out these post from the past.

What are your thoughts?

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