Root cause analysis with Cause & Effect Chain and 5 Whys
Root cause analysis is one of the most popular tools in the problem solving process. And, the majority of people, honestly believe that once the root cause is found, the problem is solved. That is an incorrect statement. In this article, we want to explain why.
What is the root cause?
First, we should understand what the root cause actually is. In our vision, the root cause is not necessarily the fundamental reason for the problem. We like to split the definition into two reasons:
Fundamental Reason of the Problem (FRP) – this is the original source of the problem. Addressing this reason usually does not change the current situation, but may help with it in the future.
Auxiliary Reason of the Problem (ARP) – any reason in the chain of events that if removed the current problem will be solved, but there is a chance that the problem will occur in the future.
Root cause analysis in PRIZ Innovation Platform
PRIZ Innovation Platform offers two instruments for root cause analysis: 5+ Whys and Cause & Effect Chain. Both of these tools have a slightly different approach to the analysis.
Cause & Effect Chain
Cause and Effect Chain (CEC) analysis is performed by answering the question “Why?” allowing the creation of chains and branches to cover all possible directions for the reasons that may cause a problem. The result is a tree displaying the causality between different components or events.
Besides being a thinking and brainstorming tool, the CEC analysis is an excellent way to learn how the system operates. CEC is recommended for the very beginning of the problem investigation.
Some example for what CEC can be very useful for include:
Sudden production yield drop
A sudden substantial increase in the number of defects
Unpredicted reliability issue
Projects to resolve/reduce chronic problems:
Continuous safety improvement
Insufficient production yield
High cost of the production
New products and services development
In some cases, CEC can also be used for problem definition; therefore, the investigation process can start from failure. The example of CEC analysis is shown below. The problem under the investigation is “Product cost is too high”:
5+ Whys is a modification of the classical 5Whys method. The analysis is done by answering the question “Why?” moving sequentially from the target disadvantage (Problem) down to the problem’s fundamental reason. There are several features of the 5+ Whys tool:
The number of steps is not limited to 5; hence the name.
The diagram is linear
The end of the chain is a dead-end, which is FRP. A dead-end can be easily identified – if a reason cannot be changed (for example the density of Cu is higher than the density of Al) it means it is a dead-end – FRP
Each step in the linear chain can be considered as an auxiliary reason for the problem (ARP)
Each ARP can be accepted as a root cause allowing to solve the current problem
The typical example of 5+Whys tool is shown below: