The art of root cause analysis – All You Need to Know

I like to say root cause analysis is an art, because in my experience, the real problem within any organization is not that we don’t know the solutions, usually the real problem is that we don’t know exactly the real root causes.

We tend to be blind to some causes that seem to be obvious for other people. As we don’t see them we don’t analyze them, so the solutions we apply often are just Band-Aids that only hide for a while the real root cause. In the end the problem goes back and we keep wasting time and money.


So what is it actually a root cause?


A root cause is an underlying cause. As Dr Edwards Deming used to say, “If you want to control your destiny: always you can understand variation everywhere”. Problems appear when we have variations to usual systems or procedures, so in order to solve those problems we look for the causes. As I was saying before, we can just look for the first cause that comes through mind, or train our teams to do thorough analysis every time we have an issue, so as to make sure we always solve it right the first time.

Edwards Deming, as statistician, also would like to say there were two main kind of causes, common and special.

Types of root causes

Common or Environmental causes tend to be the 85% of the cases: are called common because affect equally all workers in a section. Common causes are poor light, humidity, vibration, poor food on cafeteria, absence of a real quality program, poor supervision, poor instruction, procedures not suited to the requirements, poor arrangements for comfort of workers. They are faults of the system, so they usually stay there until they are removed by management. Employees cannot change the lighting, nor write new contracts for raw material or call for action at a high level.

Special or local causes (the other 15%) are specific to a local condition. In many cases, they can be corrected on statistical signal by employee himself. Signals tell him weather to leave the process as it is or to take action.

Common causes are more difficult to identify that special. When all special causes have been removed, there remain common causes.

Once a common cause is identified, management must decide whether it be economically feasible to change it. Management obligation is to focus attention on common causes of variability, but in many companies employees are the first to be blamed when only 15% of the times is under their responsibility to resolve!

So if we really want to get rid of quality issues, the art of root causes analysis should be managed accordingly to be able to identify the real root causes, and determine if they are common (management to fix) or special (employee to fix). If you are a six sigma practitioner, you will do this in the analyze phase of your DMAIC.

Tools to identify root causes

My recommendation is to work in teams to solve issues, inviting experts, managers and operators, depending on the severity of the problem, so as to make sure you have ideas from anyone involved, but considering your effort is worth the benefit (usually it is). A flip chart or a computer shared in a big screen will help you collecting the ideas and keeping record of them.

    • 5whys: To identify the root cause of a problem Toyota’s Taiichi Ohno urged workers to ask “Why” five times. Describe the problem as a question, ask “why” (what are the first level causes of the problem?), write each cause, for each cause, ask “Why” again and keep asking “Why” until no more answers can be suggested. By the time you have asked “Why” five times, you are usually at the root cause. Use the final causes suggested to generate possible solutions, and use data to accept/reject each proposed cause.
    • Fishbone diagram: (or Ishikawa diagram) decomposes a problem into potential logical causes. From the Fishbone, we need to test the most likely candidates. You can use the 5whys to drill down on each main cause to make sure you get to the very underlying cause. Your team can use “multi-voting” to narrow down the list, and then test the chosen option. This technique is effective and simple.

fishbone diagram root cause analysis

  • Control chart: it is a more sophisticated tool but really useful to objectively identify common vs special causes. Control charts are normally used to control processes (DMAIC control phase), but they can also be used to analyze processes and improve them. Most processes are not under statistical control, so attentive use of control charts can identify assignable causes. They will only detect processes out-of-control, not why the process is out of control, but is a good way to start. Once you detect you have an issue, you can use the 5whys or fishbone diagram to understand why it happened. Common causes will generate most of the variations in your chart, but special causes will be very clear, so that any employee can detect them by himself. When a new data point falls outside the control limits or violates one of the rules it is an indication that a special event has occurred. The rules are: 6 or more consecutive points all going up or all going down indicate a trend, 8 or more consecutive points all on one side of the average indicate a process shift has occurred and 14 or more consecutive points alternating up and down indicate a process which is being over controlled

Root cause analysis is designed to help identify not only what and how an event occurred, but also why it happened. Understanding why an event occurred is the key to developing effective solutions. Identifying root causes is the key to preventing similar recurrences.

Try root cause analysis yourself with these tools and let us know how it goes, or contact us to help you out!


Luciana Paulise
CEO Biztorming Training & Consulting

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