What is root cause analysis and which methods are commonly used?

• A. 5 Whys, fishbone (Ishikawa), and fault tree analysis.
• B. 5 Whys only.
• C. Fishbone (Ishikawa) only.
• D. Fault tree analysis only.

Answer: (A)

Root cause analysis is the systematic process of identifying the underlying causes of a problem, rather than stopping at symptoms, so that effective corrective actions can be taken. The best answer includes multiple commonly used methods that cover different depths and styles of analysis.

Five Whys is a straightforward technique that digs deeper by repeatedly asking why something happened until you reach a fundamental cause. It’s quick, helps teams uncover simple, chain-like causal relationships, and is especially useful for process issues and ongoing improvements.

The fishbone diagram, also known as the Ishikawa diagram, organizes potential causes into categories such as people, processes, equipment, materials, environment, and management. This visual tool helps teams brainstorm broadly and structure thinking about how different factors might contribute to the problem, making it easier to spot gaps and relationships.

Fault tree analysis takes a more formal, deductive approach. It starts with the undesired event and works downward through a network of logic gates (AND, OR) to map how combinations of causes can lead to the event. This method is powerful for complex systems and can support quantitative risk assessment and prioritization of mitigations.

Using these methods together gives a spectrum from quick, qualitative inquiry to structured, quantitative analysis, which is why they’re commonly used in root cause investigations. Relying on only one method misses the breadth of approaches available to uncover different kinds of root causes.