What type of chart is most useful for displaying data trends over time to monitor quality indicators?

• A. Pie chart
• B. Control chart
• C. Bar chart
• D. Scatter plot

Answer: (B)

Tracking how a quality indicator behaves over time requires a chart that both shows time-ordered data and signals when the process might be out of control. A control chart does this by plotting each data point in chronological order and adding a center line (the average) plus upper and lower control limits. When data stay within those limits and show only normal, random fluctuation, the process is considered in control. If points drift, form trends, or go beyond the limits, these signals help you detect special causes that may need investigation or corrective action. This time-based signaling is what makes a control chart the best tool for monitoring quality indicators over time.

Pie charts describe parts of a whole at a single moment and don’t convey changes over time. Bar charts compare values across categories and, while they can show time in a sequence, they don’t provide built-in control limits or the ongoing signal analysis needed to assess process stability. Scatter plots illustrate relationships between two variables and aren’t designed to depict a time-ordered trend for ongoing quality monitoring.