Which Six Sigma tool is primarily used for root cause analysis?

The fishbone diagram, also known as the Ishikawa diagram, is a powerful tool for identifying and analyzing potential causes of a problem in a structured way. It helps teams visually map out the various factors contributing to an issue, categorizing them into major areas such as people, processes, materials, and environment. This systematic approach allows teams to delve deeper into each category and explore the causes in detail, making it easier to identify root causes.

In contrast, the other tools listed serve different purposes in the Six Sigma methodology. The Pareto chart helps prioritize issues based on their frequency or impact, promoting focus on the most significant problems; the histogram provides a graphical representation of data distribution but does not specifically tackle root cause analysis; and brainstorming sessions generate ideas and potential solutions but lack the structured approach that the fishbone diagram provides for analyzing root causes. Thus, the fishbone diagram stands out as the primary tool for root cause analysis in Six Sigma.