Limitations of 5 Whys in CAPA and Root Cause Analysis

Limitations of 5 Whys in CAPA and Root Cause Analysis

April 15th, 2013 // 8:01 pm @

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April 15, 2013

FDA’s Quality System Regulation, and also the Quality Systems Approach to cGMP Regulations require CAPA (21 CFR 820.100) with root cause analysis as a reactive tool for quality system improvement to make sure such problems do not recur.

Many in the pharmaceutical industry know the root cause analysis system called the 5 Whys. It was created at Toyota and has been implemented in many other industries that use lean manufacturing concepts. Unlike some of the more complex root cause analysis systems, 5 Whys does not require any data segmentation, regression, testing of hypotheses or other high end statistical tools. In many instances, using the 5 Whys can be done without any data collection either.

The idea is by asking ‘why?’ at least five times, you can peel away many layers of symptoms and get to the root cause at last of a problem. At Toyota, the 5 Whys is still important for solving problems, and is the basis of the scientific approach at Toyota. In their experience, repeating ‘why?’ 5 times will usually reveal the nature of the problem.

The idea of solving a problem means that you identify the root cause of problems and then come up with and implement solutions to eliminate the root cause and to prevent them from happening again.

Note that root causes are different from casual factors. These factors contribute to the problem, but did not always actually cause the problem. Causal factors and chains should be studied and analyzed to determine what their root causes are. A strong problem solving technique has to identify the causal factors but also needs to uncover the root cause underneath the causal factors.

The 5 Whys is easy to apply and use. So it is a very practical tool in root cause analysis. You can often get to a root cause fairly quickly with this system. However, you should remember that ease of using the system and speed have to be balanced with failure risk of the problem recurring if the 5 Whys does not work.

One problem with the 5 Whys is that it does not always uncover the root cause when the cause is not known. Also, the 5 Whys presumes that each symptom has one cause. This is not always true, so this type of analysis does not always show several sufficient causes that are causing the symptom.

And, how well the 5 Whys works depends some on the skill of the person using it. If one why has an incorrect answer, it can throw off the entire analysis. Last, this method is not always repeatable. Three people applying the 5 Whys can often come up with different answers.

Other disadvantages include the inability of this method to tell between causal factors and the root cause, and a lack of rigor where the user is not mandated to do sufficiency testing.

Some possible improvement in the 5 Whys include:

  • Gather data and evidence to demonstrate the answer to any of the whys is likely and plausible
  • Couple analysis with good risk assessment
  • Come up with a timeline of events that detail how the problem happened.

When you gather evidence to support an answer to any Why, it is a good idea to not fall back to deductive thinking and reasoning to answer one of the Whys. You also should add a test loop to every Why level that attempts to validate the answer through evidence.

A risk assessment with your 5 Whys will allow you to cut down on the weakness in the method were the true root cause is not found. If the 5 Whys does produce a likely root cause but there is uncertainty if it is the true root cause, a risk assessment can be useful to see if a more stringent root cause analysis should be used to do more analysis.

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