Which of the following is considered a common statistical tool used in Six Sigma?

The correct choice, a histogram, is a fundamental statistical tool frequently utilized in Six Sigma methodologies. It visually represents the distribution of numerical data by portraying the frequency of data points in specified ranges, or "bins." This feature allows practitioners to easily observe patterns, trends, and variations within the data, which is critical when identifying process issues or opportunities for improvement. In Six Sigma, understanding data distribution informs better decision-making and can highlight areas where processes may deviate from expected performance levels.

While other tools listed have their applications, they do not serve the same primary statistical purpose in the context of Six Sigma. For instance, a Pareto chart is used to identify and prioritize issues based on their impact, and while it’s important in the problem-solving process, it doesn't inherently convey the same depth of data distribution insights as a histogram. A Gantt chart is a project management tool that outlines the timeline of project tasks, and does not focus on statistical data representation. A pie chart illustrates parts of a whole but is less effective in conveying detailed frequency distribution of continuous data, which is often necessary in a Six Sigma analysis. These distinctions affirm why the histogram stands out as a vital statistical tool in Six Sigma practice.