iSixSigma

Root Cause

Definition of Root Cause:

Over the last two months, you’ve noticed that you’re filling up the delivery trunk gas tank more often. You find this strange, as your driving frequency and routes have not changed. What’s the cause? 

You look at the dashboard and read that the miles per gallon metric has changed from 25 mpg to 17 mpg. That explains why fill-ups are happening more often.

…or does it? What is the root cause of this problem?

An overview: What is a root cause?

A root cause is the factor that causes a particular situation, such as a non-conformance. When a root cause is properly addressed with process improvement techniques, the results return a situation or metric back to the desired conforming results.

It’s common for a symptom to be confused with a root cause. A symptom is a signal or indicating factor that may exist because of the root cause, but by itself is not the cause. 

For example, you notice that more visits to the gas station have been required for a car, even though travel usage has not changed. Upon investigation, you notice that the miles per gallon metric has changed from 25 mpg to 17 mpg. The change in efficiency is a symptom, and not the cause of the problem. With more investigation, you find that the tire pressure is not set to specifications and is too low. This is the root cause, as the incorrect tire pressure is leading to the change in gas efficiency.

To fix the actual problem, one must address the root cause, which in the above case is to fill the tires up to specification levels. Having the correct air pressure will lead to a noticeable improvement in efficiency.

The danger lies in when the symptom, instead of the root cause, is addressed. In this example, the driver can improve the miles-per-gallon efficiency by making changes with driving habits, such as no longer warming up the car prior to driving in the winter or driving at slower speeds. These can improve the miles-per-gallon efficiency somewhat, but at the cost of employee comfort and delivery speeds — and they do nothing to address the true root cause, which is incorrect tire pressure.

It’s critical during the investigation of a problem to reach all the way down to the root cause and not stop the investigation with one of the symptoms.

Some benefits of attending to root cause 

Reduce total cost

When financial metrics are not being achieved, identifying the root cause allows a team to address the true reasons for the failure and stop spending unnecessary money as quickly as possible.

Reduce lead time

If on-time delivery or other time-related metrics are not being met, there must be an underlying reason. Once the root cause is identified and the problem addressed, the company can go back to operating in a timely manner.

Improve quality

The root cause of quality issues can often be hidden or impacted by more than one significant factor. By regularly using the right tools, the root cause can be identified and the non-conformances minimized.

4 effective tools to determine root cause

  • Some of the simpler tools to use to help reach the root cause are the 5 Whys technique and the fishbone diagram. The 5 Whys involve solving multiple questions that contain the word “Why,” continuing to ask the questions until they lead to either a dead end or the root cause.
  • A fishbone diagram is a method to group possible causes into categories, looking for signals due to quantity within a category, and making the process easier through the visual presentation of the causes with the problem.
  • Another useful tool is the Pareto chart. This chart helps demonstrate the frequency of possible causes, demonstrating relative significance. It’s typical to use the 80/20 rule and address the causes that make up 80% of the cases. A variable on the pareto chart is the Paynter chart, which adds an over time component between measurables to help look for interdependencies and to demonstrate how improvement efforts have addressed difference non-conformances.
  • More complex systems may require tools such as the FMEA, or failure mode and effects analysis. This tool helps identify the severity, likelihood, and ease of detection of a non-conformance in order to focus limited process improvement resources to the largest risks.

Frequently Asked Questions (FAQ) about root cause

How do I know I’ve reached the root cause?

This may be difficult to know with complete certainty. The key is to push hard when asking if there’s another underlying factor that is impacting the situation. 

This is where using the 5 Whys is critical, as the technique forces users to ask that question repeatedly. When there seems to be no further deeper questions to ask, and where it appears clear that the answer has a direct correlation with the problem, you’ve likely arrived at the root cause.

Can there be more than one root cause?

There can be multiple causes for a non-conformance, but there’s typically only one issue that’s considered the root cause. Whatever cause has the largest negative effect on the non-conformance is considered the root cause, because you’ll see the largest improvement when the root cause is addressed. 

That said, there are often problems in the real world where two or three causes all significantly impact a non-conformance. The 80/20 rule applies here, where if a small group of causes make up 80% of the cases of non-conformance, they should all be considered for improvement efforts.

We addressed the root cause, but the inefficiencies didn’t improve. What went wrong?

There are a few things that may have gone wrong. One might be that the root cause identified was not the true root cause, but instead was a symptom. 

A second consideration is that there may have been multiple impactful causes, and fixing only one did not have the impact desired because the others are still in play. 

Third, the implementation of the solution may be the issue, either because the solution did not properly address the root cause, or the changes made were not maintained properly.

Root cause is key to identifying the best corrective actions

You need to correctly identify the root cause of an inefficiency in order to derive a solution that will minimize or eliminate a non-conformance. Be sure to take your time, because when the root cause is incorrectly identified, the team is unlikely to find an optimized solution, which leads to wasted time and effort. 

There are many different tools available for determining the root cause, so be sure to choose the right tool(s) for your situation. Addressing root causes will greatly assist with reducing total cost, lead time, and quality non-conformances.

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