Conducting a Root Cause Analysis Using Lean Manufacturing Principles


November 24, 2015

lean manufacturing principles

To achieve continuous process improvement, your organization needs a proven method for uncovering the root cause of nonconformances. A root cause analysis (RCA) can incorporate a wide range of quality methods that ultimately help identify what, how, and why an event occurred so that you can take the necessary steps to ensure that it does not repeat. The RCA process includes four basic steps:

  • Collecting relevant information about the nonconformance
  • Charting the causal factors
  • Pinpointing root causes
  • Developing and recommending solutions or corrective actions to address the root cause

If your organization has embraced lean manufacturing principles, then you are likely ahead of the curve in producing what is needed, when it is needed. You have learned that lean techniques, when successfully implemented, can help your organization reduce waste and improve process efficiency.

Fishbone Diagrams

One of the easiest lean methodologies to use is the fishbone diagram, also commonly referred to as an Ishikawa or cause-and-effect diagram. This simple method helps an improvement team discover various potential causes for a nonconformance and is often used in combination with brainstorming activities. Creating a fishbone diagram is beneficial because it:

  • Is a team exercise that incorporates the ideas of all members
  • Helps sort ideas into organized categories
  • Results in an easily understood visual of the potential root causes of a nonconformance

There are just a few steps involved in creating a fishbone diagram with members of your improvement team or committee:

  • Jot down the problem statement (the nonconformance) on a flipchart. Then draw a box around the statement with a horizontal arrow running to it.
  • Next, group members share their thoughts by brainstorming the main categories of causes that may be contributing to the problem at hand. Categories could include machines, people, or materials.
  • Each category of a potential cause becomes branches from the main arrow.
  • Group members continue to brainstorm all the potential causes by asking, “Why does this happen?” The ideas generated become branches to the appropriate category or categories.
  • Participants continue to ask “Why does this happen?” about each cause. Any sub-causes then branch out from the primary causes, thus creating the fishbone appearance. Continue to ask “Why?” to develop deeper levels of causes and to identify causal relationships.

Keep Asking Why

You will notice that asking the question “Why?” plays a key role in developing a fishbone diagram to uncover root causes. This action fits nicely with advice from noted quality guru Shigeo Shingo, who said, “A relentless barrage of ‘why’s’ is the best way to prepare your mind to pierce the clouded veil of thinking caused by the status quo. Use it often.”

Asking why not only is an important part of the fishbone diagram technique, but also is the foundation of 5 Whys analysis—another effective method for determining root causes. Remember, however, that 5 is not a magic number; it may take fewer why questions or several more to actually determine the root cause of your nonconformance. By asking why approximately five times though, you can drill down more easily to the root of the nonconformance. Five Whys analysis is also useful for discovering relationships between various root causes of a single nonconformance, and it is a simple method that does not involve statistical analysis.

Another effective problem-solving method is the eight disciplines (8D) model, which is useful for identifying, correcting, and ultimately eliminating recurring problems, and it is effective for both product and process improvement. The 8D approach establishes a permanent corrective action based on statistical analysis of the problem and focuses on the source of the problem by determining its root causes. 

Ensuring Long-Term Results

Once the root causes of a nonconformance are uncovered and corrective actions are implemented, the next goal is ensuring that your solutions are maintained for the long term. If your organization has a layered process audit (LPA) system, consider focusing some of your audit checklist questions on processes associated with the root causes of your most critical nonconformances. LPAs offer an excellent mechanism to verify and sustain your corrective actions. 

By coordinating your lean initiatives with your RCA efforts, your organization will be well on its way to long-term quality improvement.

Root Cause Analysis Guidebook