According to the PMBOKGuide, Control charts are the primary tool and technique used within the Control Quality (formerly Perform Quality Control) process to determine whether or not a process is stable or has predictable performance.
* How it Works: A control chart displays process data over time and against established control limits, which consist of a centerline (the mean), an upper control limit (UCL), and a lower control limit (LCL).
* Predictability and Stability: A process is considered " in control " and predictable if the data points fall within the control limits and do not exhibit non-random patterns (such as the " Rule of Seven " ). If points fall outside the limits or show erratic trends, the process is considered " out of control " and unpredictable, requiring investigation into " special cause " variation.
* Analysis of Other Options:
* A. Cause and effect diagram (Ishikawa/Fishbone): Used to identify the potential root causes of a specific problem or effect, not to measure process stability over time.
* C. Pareto chart: A specific type of histogram ordered by frequency of occurrence. it is used to identify the " vital few " sources that are responsible for causing the most defects (the 80/20 rule).
* D. Histogram: A bar chart showing a graphical representation of numerical data distribution.
While it shows the central tendency and dispersion, it does not show the data over time to determine process stability or predictability.