Six Sigma Green Belt Certification Practice Exam

While reviewing an X-bar control chart, you notice a set of seven consecutively decreasing points. What could have caused this behavior?

1. New machine operator

2. Incorrectly calculated control limits

3. Machine deterioration

4. Process is over-controlled

The correct answer is: Machine deterioration

In the context of an X-bar control chart, observing a pattern of seven consecutively decreasing points suggests a potential underlying issue with the process being monitored. This scenario indicates that the process may be experiencing deterioration or a shift that is causing the outputs to trend downwards consistently over time. Machine deterioration could manifest in various ways, such as wear and tear in the machinery, changes in the operational environment, or material fatigue. These factors can lead to a decline in performance, resulting in lower quality or reduced outputs, reflected in the control chart as a consistent downward trend. This specific pattern, often referred to as a "run," could indicate that the process is not behaving as expected and that it is necessary to investigate the causes further. In this case, identifying machine deterioration as the reason for the observed behavior highlights the importance of equipment maintenance and monitoring to ensure consistent quality and performance in manufacturing processes.