Root cause analysis is a collection of tools and processes we can use to determine the most important causes for an issue we are trying to resolve. This is an important function as one of the top 5 reasons for project failures is poor root causation / no root cause identified. If we can identify the root cause to an issue, we have a good chance of solving it.

“Take away the cause, and the effect ceases.” – Miguel De Cervantes in Don Quixote.

Types of Root Cause Analysis Tools:

Getting Started with Root Cause Analysis

Before diving in with the aforementioned tools, it’s good to start with Causal Theory. In other words, Why does a certain problem exists?

To do this we start with a basic equation; Y = f(x) ;

Y is the Output of a process.
X are the Process elements that influence Y

Another way to state this is

Y is the crime ; X’s are the suspects that explain the crime of Y

Data door & Process door

Some of my instructors refer to the data door and the process door. Both can be used to get to root causation but certain tools are better in certain circumstances.

Effectiveness project – use data door.
Efficiency project – use process door.

Root Cause Analysis: Open-Narrow-Close

To validate root causes identified in the Open-Narrow-Close efforts, the team should employ three tools/techniques:

Open phase

In the open phase you want to gather as many ideas as possible. To do that you might use a cause and effect diagram.

Generate as many suspects (people of interest) , Brainstorming (Cause and Effect Diagram, Fish Bone Diagram)

Narrow Phase

Narrow (SME of the team) – eliminate duplicates, narrow thru multi voting to get to a narrower list

– 5 Ys to break biggers Xs to smaller managable X’s

Close Phase

Close – validate using Hypothesis and convict them or set them free

Validated X’s will be worked on to IMPROVE

Potential Cause List

Problem Identification

Use the following in problem identification:

  • Check Sheets: usually identify where and how often problems appear in a product or service.
  • Pareto Charts: identify the most frequently occurring problems or defect.
  • Project Charters: a method of problem identification in the sense that it clearly documents the scope and business impact of the problem the Six Sigma team is attempting to solve.

Use this to summarize your results at the end of the Analyze phase.

Put the diagram of the current process steps, defined outputs & the factors influencing those outputs, and a table listing the results of process analysis. Include all data sources used, how data was collected and the tools used in analyzing the data (hypothesis testing).

Prioritization of Potential Causes

  • Consider
    • Process knowledge gained (SIPOC, process map, value stream map.)
    • Past experiences (Voices)
    • Frequency (data)
    • Whether the cause can be controlled or even measured.
    • Personal bias in logic.
  • Do NOT Consider
    • If a potential solution exists for the potential cause.

Root Cause Analysis Videos

Good video, awful sound. I muted it and just clicked through at a good pace. It gets the point across.

Other Helpful Notes

Also see Linear Regression for Y = f(x)

Also see Causal Theory=f(x)

Also see Hypothesis Testing


Comments (6)

For a failure there may be so many causes -but the cause or causes identified for the current failure is called the root cause .
Corrective action to be taken in such a way that will not occurring again ie avoiding recurrence.
Preventive action is the one what we take before the occurrence of that event ie avoiding occurrence.

My Question is when to initiate a root cause analysis and when to find causes through application of six sigma ?

Hi Fahed,

In Six Sigma you generally follow the DMAIC paradigm – Define, Measure, Analyze, Improve, and Control.

You would do root cause analysis in the Analyze phase.

Does that help?

Best, Ted.

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