Choose the correct answer:In Six Sigma analysis, the distinction between "common cause of variation" and...

In Six Sigma and statistical process control, which are often referenced within Object Management Group (OMG) Business Process Management practices for performance measurement and process capability analysis, variation in a process is categorized into two types:

Common cause variation (natural variation)

This is the inherent, stable variation built into the process.

It reflects the normal, expected fluctuations when the process is operating in a state of statistical control.

On a control chart, data points that reflect only common cause variationremain within the control limits (UCL and LCL)and do not exhibit specific non-random patterns.

Special cause variation (assignable variation)

This arises from specific, identifiable factors not normally part of the process (e.g., equipment failure, operator error, unusual input material).

On a control chart, it is typically indicated by pointsoutside the control limitsor by defined abnormal patterns (runs, trends, cycles) even if still inside the limits.

In the diagram shown:

The horizontal center line represents theprocess average.

The upper and lower horizontal lines representUCL (Upper Control Limit)andLCL (Lower Control Limit), typically set at ±3σ from the mean.

Zones A, B, and C mark bands of 1-sigma increments from the mean but are allwithinthe control limits.

From a standard Six Sigma / SPC standpoint, and consistent with how OMG-based BPM measurement and control concepts are applied:

All data points inside the UCL and LCLare considered to be a result ofcommon cause variation, provided they do not exhibit specific rule-violating patterns.

Data points outside the UCL or LCLare not common cause; they are indications ofspecial cause variationthat must be investigated and corrected.