Six Sigma Green Belt Certification Practice Exam

What tool is commonly used to assess whether a process is in control?

1. Control chart

2. Fishbone diagram

3. Histogram

4. Pareto chart

The correct answer is: Control chart

A control chart is a fundamental tool used in Six Sigma to monitor processes over time. It helps in determining whether a process is stable and statistically in control or if there are variations that signal opportunities for improvement. The main purpose of a control chart is to differentiate between common cause variations, which are inherent in the process, and special cause variations, which may indicate problems that need to be investigated. Control charts plot data points over time and include control limits, which are statistically derived boundaries that help in visualizing the process's performance. When data points stay within these control limits and show a random pattern, it indicates the process is in control. Any data points that fall outside these limits or show non-random trends are signals that further investigation is needed. In contrast, other options like the fishbone diagram, histogram, and Pareto chart serve different purposes. The fishbone diagram helps identify the root causes of a problem, the histogram provides a visual representation of the distribution of data, and the Pareto chart is used to prioritize issues based on their frequency or impact. None of these tools are used specifically for assessing process control over time.