A process that is stable can best be identified through the use of a:

The NAHQ CPHQ exam blueprint identifies the Shewhart control chart as the primary tool for determining whether a process is stable and in statistical control. A stable process demonstrates only common cause variation, meaning variation inherent to the process itself.

Option A is correct because Shewhart charts include control limits, which allow quality professionals to distinguish between common cause and special cause variation. A process is considered stable when data points remain within control limits without nonrandom patterns.

Run charts (Option C) show trends over time but lack control limits and cannot confirm stability. Histograms (Option D) display data distribution at a single point in time. Scatter diagrams (Option B) examine relationships between variables.

The CPHQ framework emphasizes control charts as essential for process monitoring, improvement evaluation, and sustainability, making Option A the correct answer.