In control charts, which assertion is correct?

In control charts, the correct assertion involves their reliance on historical statistical data. Control charts are a statistical tool used primarily in quality control processes to monitor how a process performs over time. They do this by plotting data points over time based on measurements from a process or system, which are derived from historical performance data.

This historical data establishes control limits, which help in determining whether the process is in a state of control or if there are variations that signal issues needing investigation. By analyzing this historical data, practitioners can discern patterns, detect shifts that may affect the process, and make informed decisions to ensure consistent quality.

The other assertions do not accurately reflect the primary purpose of control charts. For instance, while there may be trends observable in the data, control charts do not estimate future patterns without control; they require historical data to provide context. Additionally, they don't solely indicate current performance, as they are designed to reveal variations over time rather than just a snapshot of current conditions. They also do indeed identify trends over time, contrary to the assertion that they cannot do so, as they are frequently utilized to detect shifts and trends in the process quality statistics.