Which of the following is not true regarding control charts?
(A) Control charts can be used to monitor a process for the existence of special cause variation
(B) The major components of a control chart are the lower control limits, the center line, and the upper control limits
(C) Control charts alone can determine the source of problems
(D) Control charts are similar to run charts in that data is plotted versus time.
The Correct Answer and Explanation is :
The correct answer is (C) Control charts alone can determine the source of problems.
Explanation:
Control charts are powerful tools used in quality control and statistical process control (SPC) to monitor the performance of a process over time. They help to identify whether the variations in a process are due to common causes (inherent to the process) or special causes (external factors that might be disruptive). Let’s review each statement:
(A) Control charts can be used to monitor a process for the existence of special cause variation
This statement is true. Control charts are specifically designed to detect special cause variation, which are unusual or exceptional changes in a process that could indicate problems. By plotting data points over time and comparing them to control limits, control charts help determine whether a process is in control or out of control.
(B) The major components of a control chart are the lower control limits, the center line, and the upper control limits
This statement is true. A control chart consists of three main components: the center line (which represents the average or target value of the process), the upper control limit (UCL), and the lower control limit (LCL). The UCL and LCL are statistical limits beyond which data points indicate that the process may be out of control.
(C) Control charts alone can determine the source of problems
This statement is false. While control charts are useful for detecting whether a process is out of control, they do not, by themselves, pinpoint the exact cause of the problem. They help in identifying the existence of variation, but investigating the root cause requires further analysis, such as root cause analysis, cause-and-effect diagrams, or other investigative tools. Control charts tell you when something goes wrong, but not why it went wrong.
(D) Control charts are similar to run charts in that data is plotted versus time
This statement is true. Both control charts and run charts plot data over time, which helps in understanding trends, patterns, and behavior. The key difference is that control charts include control limits and help distinguish between common cause and special cause variation, while run charts do not.
In summary, while control charts are a critical tool for monitoring processes, they are not designed to identify the specific cause of variation on their own. Further investigative techniques are necessary to diagnose the source of the problems.