Six Sigma Green Belt Certification Practice Exam

When analyzing a process using a control chart, what might a trend of eight consecutive points above the centerline indicate?

1. Random variation

2. Process improvement

3. Non-random variation

4. No specific interpretation

The correct answer is: Non-random variation

The identification of a trend of eight consecutive points above the centerline on a control chart serves as a significant indication of non-random variation in the process being analyzed. Control charts are primarily used to monitor processes over time and to distinguish between common cause variation (which is inherent to the process) and special cause variation (which indicates a change or issue). When you observe eight consecutive points above the centerline, it suggests that there is a systematic deviation occurring in the process, pointing toward an issue that is not merely due to random fluctuations. This consistent upward trend indicates that the process is behaving differently than it should, which may require further investigation to identify the underlying cause. It could be due to changes in the process, input materials, or other external factors affecting the performance. In contrast, random variation aligns with the expectation that data points would fall both above and below the centerline without exhibiting a predictable pattern. Process improvement typically suggests that changes have been implemented to enhance performance, leading to better or more stable results, but that would not be indicated by a lack of variability such as this trend. Lastly, saying there is no specific interpretation downplays the significant message conveyed by such a trend, as it clearly points to potential issues that need addressing.