In this Lightning Cast, we explore two common root cause analysis approaches, Fishbone Diagrams and 5 Whys, to help you understand when to use each technique.


A Lightning Cast is a shorter form episode modeled after lightning talks.  You’ll get valuable content in 8 minutes or less.


Are you merely treating the symptoms of a problem or you correcting the underlying cause?

Understanding the difference between the root cause and other causal factors is key in solving the right problem. Removing or otherwise addressing the root cause will prevent the problem from happening.  If we only address other causal factors, the problem may recur.

That’s why we need to apply root cause analysis.  Through cause analysis, we typically start by defining the problem.  Then we collect data and work to identify possible causes.  We then define the root cause and implement a solution to address that root cause.

There many different approaches to identifying the root cause.  Let’s focus on two frequently use approaches: Fishbone Diagrams and the Five Whys.

A Fishbone or Ishikawa diagram is a tool used for addressing common cause variation.  Common causes are the inputs and conditions that contribute to regular everyday variation of a process.

Five Whys is the most commonly recommended tool for finding the root cause of a special cause variation.  Special causes are factors that aren’t always present in a process and can appear because of some particular circumstance.


Fishbone Diagram

When investigating a common cause using a Fishbone diagram, you’ll explore several cause categories leading to the effect.  To use a Fishbone approach, first gather the right people in the room.  With varying levels of expertise and ownership, you’ll have a well-rounded conversation.

Start by drawing a horizontal line which represents a problem to be solved.  From there, draw branch categories coming out from that horizontal line.  Use those potential cause categories to brainstorm and then identify main opportunities and underlying root causes.

From the horizontal main problem line, draw six branches: process, people, measurement, environment, machinery, and material.  From there, brainstorm different issues that affect each of these branch categories.

Record the ideas on the Fishbone diagram and then prioritize the causes to define opportunities.  If you’d like, you can use a Pareto Chart to help prioritize among the common causes.  Just remember that because something is frequent doesn’t mean that fixing it is a good investment.  The cost needed to fix the issue and the potential benefit needs to be considered.


Five Whys

Now let’s turn our attention to the Five Whys technique.  You can use a Five Whys problem-solving approach in conjunction with the Fishbone diagram.  After identifying a few of the critical factors you want to address using a Fishbone Diagram, you can apply the Five Whys technique on those causes.

You can use this technique to explore the cause-and-effect relationship in the problem space.  The theory is that by asking why five times, you get to the real root cause of the problem.  By understanding and addressing the root cause, we’re able to prevent the problem from reoccurring.

When applying the Five Whys technique, don’t simply ask why five times.  Use other probing questions such as:

  • What actually occurred?
  • When did it occur?
  • Who was involved?
  • Who else needs to be involved?
  • Did we use standard practices?
  • Are there any inconsistencies between what the systems are supposed to do what it’s actually doing?
  • What assumptions do we need to test?
  • What unintended consequences can result from implementing effects?

Here’s a tip for using the Five Whys technique.  Never leave human error or personal factors as the root cause.  Remember that it’s the process and not the people that fail.

Don’t forget that you can address common cause or special cause variation through controls.  Once you determine the root cause, identify whether you can prevent their root cause or work to detect it early.

If prevention steps are too costly, you can implement monitoring to detect the issue at far less cost.  Don’t waste time fixing the problem when you could prevent it happening in the first place by focusing on quality upfront.


Listen to this lightning cast t understand when to use each root cause analysis technique.



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