What kind of variation does a control chart help identify?

• A. Natural vs assignable variation.
• B. Seasonal variation only.
• C. Random short-term fluctuations.
• D. Predictable trends only.

Answer: (A)

A control chart is about distinguishing the kinds of variation a process shows. The natural, or common cause variation, is the small, random fluctuation you expect when a process is operating normally. Assignable (special) variation comes from identifiable causes—things like a worn tool, a change in material, or human error—that push the process away from its typical behavior. The chart uses limits and patterns to signal when variation stays within normal bounds (indicating natural variation) or when something outside those bounds points to an assignable cause that needs investigation. Seasonal patterns or trends can appear, but they’re not the sole focus; the essential idea is to separate inherent variability from variability caused by identifiable factors.