The Importance of Root Cause Analysis (RCA) in Lean Six Sigma
One of the very important components of continuous improvement in all methodologies (Lean, Six Sigma, Lean Six Sigma) is Root Cause Analysis (RCA). It is very common to see executives jumping into Lean Six Sigma tools in an attempt to solve problems before doing a proper RCA. The result is that only the symptoms are addressed but the root of the problem still continues to exist. Sometimes, the problem may move from one process to another. Hence it is important to conduct a proper RCA before jumping into solutioning. The objective is to identify the cause of the problem and take steps to eliminate the cause so that it will not recur again, or move to another process.
Some of the common RCA tools are as follows:
- Ishikawa Diagram (also known as Fishbone Diagram or Cause and Effect Diagram (CED))
- 5 Whys
- Current Reality Tree (CRT)
- 8 Disciplines (8D)
Fishbone (Ishikawa) Diagram
The Ishikawa Diagram was created by Kaoru Ishikawa. It is also called Fishbone Diagram because the completed pictorial diagram looks very much like the shape of a fishbone. It is a simple and effective tool that shows the problem causes (inputs) for a given effect (output).
The causes are usually grouped into the following categories (also known as 6M):
1. Men (People) – personnel involved in the process
2. Methods – methods in which the process is performed
3. Machines – equipment / tools required for the process
4. Materials – materials required for the process
5. Measurements – measurements and data collected
6. Mother Nature (Environment) – environment in which the process operates
Fishbone (Ishikawa) Diagram is covered under Lean tools in our Lean Thinking Training.
5 Whys is a surprisingly simple but powerful technique for RCA. It utilizes an iterative interrogative technique of repeating the question “Why?”. Each answer forms the basis of the next question, until the question cannot be answered sensibly.
While it is called 5 Whys, it is not necessary to stop at 5 if further drilling down is possible. It is also not necessary to get to 5 if it is not possible to do so.
5 Whys is covered under Lean tools in our Lean Thinking Training.
Current Reality Tree (CRT)
CRT has its roots from Theory of Constraints (TOC) developed by Eliyahu M Goldratt. CRT is a logic based tool for using cause and effect relationship to determine root problems that cause the undesirable effects in a given system.
For more information on Current Reality Tree (CRT), please visit our our Root Cause Analysis Training (RCA Training) page.
The 8 Disciplines (8D) method is a problem solving approach that is widely used in the automotive and space industries. The objective of 8D is to identify, correct and eliminate recurring problems. 8D provides a framework of 8 stages and other RCA methods (such as Fishbone, 5 Whys, CRT) can use used within the 8D framework without any conflict (D4 or Stage 4).
For more information on 8D, please visit our 8D Training (Eight Disciplines Training) page.
1. Current and Future Reality Trees, Advanced Tools for Black Belts and Master Black Belts, Timothy Yoap, 2006, John Wiley & Sons Ltd
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